Recent Developments and Applications of Haptic Devices

Volume 22 (2003), number 2 pp. 117–132 COMPUTER GRAPHICS forum

Recent Developments and Applications of Haptic Devices

S. D. Laycock and A. M. Day

School of Information Systems, University of East Anglia, Norwich NR4 7TJ, [email protected]; [email protected]

AbstractOver recent years a variety of haptic feedback devices have been developed and are being used in a number ofimportant applications. They range from joysticks used in the entertainment industry to specialised devices used inmedical applications. This paper will describe the recent developments of these devices and show how they havebeen applied. It also examines how haptic feedback has been combined with visual display devices, such as virtualreality walls and workbenches, in order to improve the immersive experience.

Keywords: Haptics, Force feedback, Haptic Gloves, Exoskeleton, Workbenches, Motion platforms, LocomotionInterfaces.

ACM CSS: H.5.2 Information Interfaces and Presentation—Haptic I/O; I.3.8 Computer Graphics—Applications;I.6 Simulation and Modelling—Applications

1. Introduction

Haptic feedback is becoming more viable as the processingpower of computers increases and the technology used tobuild the haptic devices develops. The inclusion of hapticfeedback in applications has been shown in several casesto improve interaction [1–3]. This paper aims to outline themain types of haptic feedback device by illustrating a varietyof devices which are commercially available and undercurrent research. The applications in which these deviceshave been utilized will also be discussed. The aim is to showthe extent to which haptic feedback has been used and toprovide inspiration for future developments.

The first section will give a selection of terms which willbe used throughout this paper. The following sections willdescribe some of the devices currently available and theirapplications. These devices range from small one fingerdesktop devices to motion platforms capable of exertingforces on rows of seats in a theatre.

1.1. Terminology

1.1.1. Force Feedback

Force feedback links the user to the computer by applyingforces on the user. These forces are sensed by low-bandwidth

receptors. Force feedback is able to provide large forcescapable of stopping the user’s motion, for example whencolliding with a virtual wall. This paper will mainly be aimedat devices capable of force feedback, however, some devicesallowing tactile feedback will also be included.

1.1.2. Tactile Feedback

Tactile feedback is sensed by a humans receptors which liemuch closer to the surface of the skin. It is experienced fromheat, pressure and vibration. Feeling the texture of a surfaceis one example of tactile feedback.

1.1.3. Haptic Feedback

The definition of the word haptic taken from the OxfordEnglish Dictionary is; “Of, pertaining to, or relating to thesense of touch or tactile sensations.” [4]. This definitionseems to link it more closely with tactile feedback. Theterm Haptic Feedback is now widely used to include TactileFeedback and Force feedback.

1.1.4. Degrees of Freedom (DOF)

For every haptic device the degrees of freedom are specified.This quantity describes how many translations and rotations

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118 S. D. Laycock and A. M. Day / Haptic Feedback Devices

are utilized by the haptic device. A haptic mouse for instancemoves in the x-y plane and so has two degrees of freedom(DOF). Three-dimensional devices are able to translatealong the x-axis, y-axis and the z-axis and are classed asthree DOF. Three-dimensional devices which are also ableto rotate about all three axes have six DOF. Arm and handhaptic devices can have more degrees of freedom, as theforce feedback can be applied to other points such as theforearm and wrist.

1.1.5. Actuators

The actuator is the component that allows a haptic device toexert the force on the user. One of the most common typesof actuator used in haptic devices today is the electric motor.The type of actuator used is crucial to the design of anyhaptic device. A trade off has to be made between the powerthe actuator is able to produce and its volume and weight.This issue will be discussed further in the following sectionregarding the design of a good haptic feedback device.

2. Requirements for the good design of a HapticFeedback Device

In order to produce a good haptic feedback device severalrequirements need to be taken into account. It is important toexamine closely the human sense of touch when construct-ing these requirements. It is difficult to produce a completeset accurate for all devices as the ideal device requirementsvary for different devices and depend on the application.

These requirements have been compiled from the follow-ing sources [5], [6] and [7]. A common goal as set out byEllis [8] describes the need to allow unimpeded motion butto be able to exert high fidelity forces and torques. The me-chanical constraints for the device should include low iner-tia, backlash, weight and friction. When using a device it isimportant that if the contact point of the device is not collid-ing with anything in the virtual world then negligible frictionis perceived. A friction level of 5% of the force range wasset by Adelstein and Rosen during their design phase [9].The low friction enables the user to move the device freelywhen not in contact. Obtaining negligible friction can be aproblem particularly when high stiffness is required. Highstiffness implies a stiff mechanical interface which needs tobe constructed from metal. These heavy materials increasethe friction as well as increasing the overall weight of thedevice. This provides a conflict between obtaining high stiff-ness whilst keeping low friction. When considering the con-struction of a force feedback device there is a choice betweenserial and parallel mechanisms. Serial mechanisms are morecompact and can be fast. The down side is that as each sec-tion is added to the chain the total inertia increases and thetotal stiffness decreases. Parallel mechanisms do not exhibitthe above problem and have a much higher stiffness. Thedisadvantage over serial mechanisms is that the mechanism’selements can physically interfere.

Ensuring the device is statically balanced is anotherdesign consideration. This means that the centre of mass ofthe moving parts remains stationary regardless of movement.If this property can be achieved then there is no needfor active gravity compensation and the average torquerequired from the actuators is zero. The device should alsobe designed so that it does not intrude into the visual space,meeting this requirement can be difficult particularly withexoskeleton style devices (see section 5). The materials thatare used to construct such devices need to be considered.Some parts of the device will need to be strong enoughto take the stress and strain applied by the user and theactuators. Steel is often used if high forces are required;aluminium when smaller forces are required. However, thesematerials make the devices heavy, which can cause problemsfor haptic gloves, arm exoskeletons, and portable devices.

Another consideration, which affects the overall weight ofthe device, is the type of actuators incorporated. Actuators,as discussed previously, provide the forces for the device. Inmost cases a good actuator should be compact and light aswell as capable of producing the necessary power to deliverthe forces. There are tradeoffs between power, volume andweight since actuators capable of producing large forces aregenerally heavier and are larger in size than those actuatorscapable of smaller forces. The weight of the actuatorsused is a critical factor when considering portable devices,particularly when multiple DOF are required. For certaindevices these constraints can be relaxed. In motion platformsused in flight simulators the weight and size of the actuatorsis less critical compared to the greater power output thatis required. There are various actuators available includinghydraulic, electric and pneumatic. Hydraulic actuators areable to produce large forces but there is a potential hazardfrom hydraulic fluid leaks. The oil used as the hydraulic fluidmay not be safe if the device is to work in hygienic areassuch as hospitals. In the worse case the flammable liquidposses a fire risk. Pneumatic actuators tend to be much saferbut the force they can produce is limited. Electric actuatorsare the most common, as they are reasonably safe and canprovide forces suitable for many small haptic devices. Theactuators should also be backdrivable. This means that theuser should be able to move the device around withoutopposition from the actuators. This property coupled withlow friction and inertia aid in achieving unimpeded motion.

Often haptic devices will be used for long periods of timeand so they must be comfortable to use. The weight of adevice needs to be taken into consideration. If parts are veryheavy then moving them around may cause fatigue in ashort space of time particularly if the device is grounded,to some extent, on the user. The position in which the user isexpected to operate the device also needs to be considered.For small desktop devices it is important that the hand andwrist can be positioned comfortably. Many small devicesallow the wrist to be supported by the surface on whichthey sit, similar to operating a mouse. A pilot study of

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S. D. Laycock and A. M. Day / Haptic Feedback Devices 119

wrist motion was undertaken to show that a square regionof side 150 mm could be utilized as the workspace area andthat 50 g masses were acceptable for applications requiringapproximately 30 min to complete [8]. For larger devices,ensuring a comfortable position for operation can be more ofaproblem. The freedom of motion relates to the requirementthat the workspace should be sufficient for the applicationand should not restrict the user in natural movement. Forthe motion of larger devices such as arm exoskeletons thecharacteristics of the human arm need to be noted. In orderfor humans to perceive forces smoothly the device mustmatch or exceed the human sensing resolution. The jointposition sensitivity (JND – Just Noticeable Differences) forthe finger, wrist, elbow and shoulder are as follows: 2.5◦, 2◦,2◦ and 0.8◦ [10]. Another factor is the forces that are able tobe produced. The maximum forces that can be sustained forlong periods of time is particularly important. For a maletest case Tanet al. [10] determined the sustained forces tobe; wrist 64.3 N, elbow 98.4 N, shoulder 101.5 N and for afemale test case; wrist 35.5 N, elbow 49.1 N, shoulder 68.7 N(side) and 87.2 N (front).

Shimoga details five main approaches to touch feedbackthese are; Visual, Pneumatic, Vibro-tactile, Electro-tactileand Functional Neuromuscular Stimulation [11]. Pneumatic,Vibro-tactile and Electro-tactile devices will be discussedin this paper. For tactile devices the weight is even moresignificant as the parts of the device that interact with theoperator such as the array of pins in Vibro-tactile devices areattached to the operator. As mentioned at the beginning ofthis section looking at the characteristics of human touch isa critical task when designing devices. Air pockets and airrings transmit forces to the user in pneumatic devices. Thepressure produced by these devices need to be appropriatefor the human’s ability to sense pressure. This pressureshould be just above 0.2 N/cm2. The reasons for this valueis due to the fact that the human finger cannot sense pressurebelow this value and that large forces deteriorate the sensingability.

When considering Vibro-tactile devices Shimoga liststhe following properties of the cutaneous mechanoreceptorsas crucial information for the design of touch feedbackdevices: The receptors within the skin, their mean receptiveareas, spatial resolution, responsive frequency range and thefrequency for maximum sensitivity. The spatial resolution ofthe fingertip has been determined using a test called the two-point limen [7]. The average separation at the fingertip wasfound to be 2.5 mm and the palm less sensitive at 11 mm.Single-point vibrations at the fingertip can be sensed at abandwidth of at least 300 Hz [8]. Tactile devices are alsoproduced which convey temperature information to the user.Humans can experience temperature without discomfortbetween 13 and 46◦C. Typically the human finger tip cansense a temperature change of 1◦C.

3. Desktop Devices

The most common devices in use today are those whichcan be operated in a desktop environment. These devicesrange from the conventional mouse with added tactile orforce feedback to haptic gloves with limited movement. Thedifference in price range of these devices is large. The Log-itech Wingman force feedback mouse costs approximately60 EUR [13] and Immersion’s CyberGlove and CyberGraspcombination costs about 50 000 EUR [14]. The technologyand design of some of the devices available will now be de-scribed, starting with tactile feedback devices for the desktopenvironment.

3.1. Tactile Devices

Tactile devices have been in use since the 1970’s to act asaids for blind and deaf people. More recently this technologyhas been developed to provide additional information forhuman–computer interaction. The first devices to be com-mercially available for haptic feedback in the desktop envi-ronment were the force and tactile feedback mice. Logitechproduce a tactile mouse tilted the iFeel MouseMan. Thismouse is able to vibrate as the user interacts with buttons andmenus on the desktop and windows applications. The mousecan also be used with a variety of games. Some reviewershave stated that the vibrations produced by the mouse do notseem particularly natural and may in fact become tiresomein the windows environment [15]. However, very positivefeedback has also been presented with regard to its appli-cation to a variety of games. The tactile feedback that themouse exhibits is controlled by software called TouchSenseproduced by Immersion Corp.

At the University of East Anglia experiments wereundertaken with a variety of tactile mice to investigate theiruse in a collection of perceptualization tasks [16]. Tactilemice were designed with the base mouse comprising ofan Apple Macintosh single-button mouse. The feedbackwas provided through the sound channel of the MacintoshQuadro 950. Mono and Stereo speaker mice were developedusing typical personal computer speakers stripped to just thecoil, magnet and casing. The speaker could then be attachedto the side of the mouse to provide vibrotactile stimulusto an area onto which the user could rest their finger. Thepreferred mouse produced was the solenoid mouse due toits low noise and comfort of use. One experiment involvedthe user choosing a shorter line displayed within a collectionof slightly longer lines. The task was completed with andwithout the aid of tactile feedback. The results showed thatvisual clutter could be overcome with the inclusion of tactilefeedback.

Besides mice, tactile feedback has also been applied tothe input devices in laptop computers. At the IBM AlmadenResearch Centre the Tractile device has been developed [17].This device is located in the TrackPoint position on the



laptop and looks the same as the TrackPoint. An actuatoris used to vibrate inside the TrackPoint at a maximum rateof 30 Hz. The goal of this device is to produce tactilevibration with a compact design and power consumptionsuitable for laptop computers. This device has been usedin experiments to investigate the effects of tactile feedbackin steering tasks. The experiment was designed such thatthe user is required to navigate around a circular tunnelkeeping within the edges. This task is assumed to resemblemenu navigation. The results of this experiment showed thatthe steering performance was increased with the use of thetactile device and that it is important to ensure that the visualfeedback corresponds to the tactile feedback.

The use of tactile feedback is not just limited to the desk-top environment. There are several applications which usetactile feedback to aid users in a variety of tasks. In numer-ous activities where humans find themselves interacting withmachines problems can arise where the interface overloadsthe users’ sensors. Driving a car is one task which requiresconcentration on the surroundings and leaves little time tocheck the dashboard’s collection of dials. The Universityof British Columbia has developed a tactile steering wheelwhich could warn the driver of a variety of messages suchas low fuel [18]. They have undertaken experiments to showthat with the addition of tactile feedback the user is able todistinguish when warnings occur faster than visual feedbackalone. The steering wheel comprises of a pneumatic pocketcovered with a vinyl steering wheel cover. The pneumaticpocket can be inflated and deflated rapidly using a pump toprovide vibratory stimulus that can be localised to a specificarea. In most tactile devices, which use vibration as the stim-ulus, the part of the device which touches the user movesorthogonal to the users skin. At McGill University a devicewhich utilizes an array of 64 closely packed piezoelectricactuators to create lateral stress fields in the skin covering thefinger pad has been developed [19]. This device illustrates anew approach to providing tactile feedback although furtherresearch is needed to achieve the perceptions of texture fromthis device. A new design for a USB driven tactile display iscurrently being developed at McGill University. It has 100taxels at a 1 mm pitch. It is thought that it will be able tomove the skin±50µm per taxel.

In addition to tactile responses through pressure on theskin devices are also available to provide information basedon temperature. The Displaced Temperature Sensing Systemproduced at CM Research is able to provide temperatureinformation through a device attached to the fingertip [20].The device is capable of producing temperatures between10 and 35◦C. It has some interesting possibilities forapplications such as providing temperature information tothe user of a prosthetic limb or in tele-robotics.

3.2. Two and Three DOF Desktop Devices

This section includes force feedback devices which exhibittwo or three degrees of freedom. One such example isthe LogiTech Wingman force feedback mouse. This deviceallows the user to feel the graphical user interface byapplying force feedback in thex-y plane. The user is ableto feel buttons and items on the start menu and is also ableto receive force feedback when resizing a window. This is inthe form of stretching sensations similar to that of stretchingarubber band. There are several other mice available such asthe MouseCat produced by Haptic Technologies [21]. HapticTechnologies has since been acquired by Immersion Corp.This mouse was originally aimed at the visually impaired,to allow them to operate a computer with a graphicaldisplay which could be felt via the mouse. The MouseCatis supplied with software which allows the user to interactwith the Windows environment and extra sounds are playedfor the icons on the screen. This software is known asTouchWindows. Tests have shown that users learn Windowssignificantly faster when using this software [21].

Another inexpensive category of devices is the force feed-back joystick. The ordinary joystick which provides no forcefeedback delivers only information regarding the position ofthe stick. There are two main types of configurations forjoysticks; these are Spherical Jointed Joysticks, which useonly rotations, and Cartesian configurations that allow trans-lations as well as rotations. Cartesian joysticks have the ad-vantage of a larger workspace and the ability to translategiving increased mobility to the user. However, they alsoneed an increased amount of desk space.

There are several types of joysticks available for personalcomputers. Microsoft has produced the Force feedbackjoystick called the Force Feedback 2 [22]. This device costsapproximately 100 EUR and contains a 16 bit 25 MHz onboard processor. As well as being applied to games thisdevice has also been adapted for the rehabilitation of patientswith brain injuries [23]. The Joystick has been adapted withthe addition of a handle designed for patients less able to gripthe original handle of the joystick and with a support for theuser’s arm. The main advantage of this system is the abilityto allow patients to use the programs over the Internet (in theform of Java Applets), to provide personalised programs oftherapeutic exercises.

Force Feedback is becoming increasingly popular ingaming with 12% of all personal computer games beingtouch sense enabled [24]. Joysticks and Mice are some of thedevices used in these games. Over 200 games are availablefor the SideWinder Force Feedback 2 Joystick. There arealso other devices such as the SideWinder Force FeedbackWheel retailing at approximately 180 EUR. Force feedbackis provided through a steering wheel to allow the user toexperience a variety of sensations including the roughnessof the terrain. Logitech have also produced a very successful



force feedback wheel, the GT, which sold over 350 000. Itssuccessor the Driving Force wheel was released in 2001for the Playstation 2 retailing at 130 EUR and is expectedto be popular. For a variety of force feedback devices forthe games industry see [25] [26]. Other larger devices arealso available in the entertainment industry and these will bediscussed in later sections. In 1999 Immersion released theImpulse Engine 2000 a two DOF joystick. It consists of a13 cm hard plastic handle mounted on top of a metal box.It is marketed as a research quality force feedback joystickexhibiting smooth drive torque with minimal complianceand friction [27]. Two or more devices can be interfaced withasingle system allowing for joint participation in tasks suchas surgical simulations.

Joysticks and mice are common interfaces but manyhaptic devices have been designed which adopt a novelapproach. The first of this type of device to be discussed iscalled the Pantograph [28]. It has two degrees of freedomand was developed at McGill University, Montreal. Thisdevice was originally conceived in 1993 with the followingrequirements: a large work area, simplicity and fidelity. Thedevice uses a simple five-bar linkage that is characterisedby an acceleration response. It has negligible friction andso when no forces are applied the impression of slidingover an icy surface is detected. Several versions of thisdevice have been developed, the original was designed forthe rehabilitation of the visually handicapped in an officeenvironment. In 1995 a smaller version was developed whichwas used in experiments in micro gravity. Recently thePantograph has been redesigned to allow for a resolution of10µm or less.

The devices described in the preceding sections all workin two dimensions. The interaction of current graphical userinterfaces is in two dimensions and has been for manyyears but humans operate in three dimensions. The twodimensional interface constrains the user from being ableto interface with the computer as naturally as possible.Computers are nearing the stage where three-dimensionalinterfaces and three-dimensional force feedback devices arebecoming a viable option for the average computer user.Today the rendering of a virtual environment can almostbe completely left to the graphics card and today’s 2 GHzprocessors can replace the dual processor systems that usedto be required.

Force feedback devices capable of working in threedimensions will now be discussed. The next generation ofpersonal computers will be able to effectively utilize thesedevices. However, the constraining factor will be the costof a three-dimensional force feedback device. We will startour discussion with a device that does not have actuatorsfor each DOF, but is able to give the user the impressionof three dimensional force feedback. It is called the PenCat,a two and a half degrees of freedom device produced byMcGill University [29]. Forces are applied to the degrees

of freedom in the horizontal plane. The vertical movementsare passively actuated by an elastic return. This device hasthe ability to make the user believe they are touching three-dimensional surfaces when actuators are only providingforces in two dimensions.

Most haptic devices have some static friction, whichaccounts for approximately 5% of the output. The Maglevis a magnetically levitated joystick [30]. This device usesLorentz actuators that ensure no friction is perceived. Theentire device is contained in a desktop height cabinet. Theuser interacts with a single moving part located in thecentre of a bowl mounted in the top of the cabinet. Onedisadvantage of the Lorentz actuator is the fact that heatingoccurs when electrical current flows through for long periodsof time. This means the device can only be used accuratelyfor short periods of time. The work area of this device isrelatively small, 15–20 degrees of rotation and 25 mm oftranslation is the range of motion available. It gives theuser restricted movement but is useful for many desktopapplications, particularly those which require small forces.The reason is that as friction is non-existent in the device itallows small forces to be perceived accurately.

FCS Control Systems have recently produced the Haptic-Master [31]. A three DOF force controlled robot arm capableof a maximum force of 250 N. The ability to produce largeforces coupled with a maximum deceleration of 50 m/s2

allow high fidelity contacts to be perceived. This device isaimed at applications such as simulation and training, reha-bilitation and virtual design. It was found to perform verywell in terms of the fidelity of forces when operated by theauthor. When colliding with complex polygonal models suchas a tooth the feeling of every part of the tooth seemed veryrealistic. The final device to be discussed in this section isthe Excalibur device a linear haptic display [32]. This deviceoperates on a larger scale compared to the rest of the de-vices already mentioned with the workspace area measuredat 300×300×200mm. It is able to provide a continuous forceof 100 N or a peak force of 200 N. The device is constructedon a large square surface with guide rails along each edge.The device only exhibits three DOF but with large forcecapabilities it would be well suited to telerobotics, mainte-nance analysis and CAD style applications.

3.3. Five-Seven DOF Desktop Devices

The devices discussed previously allow the user fairlylimited movement in terms of DOF and the work area, withthe exception of excalibur. The next set of devices are thosewith slightly larger work areas and between five and sevenDOF. The first category concerns those devices which aremanipulated using a tool of some kind. This can be a penbased device or a device which allows the user to attach aspecific type of tool corresponding to the application. Theadvantages of the pen based device are; it is familiar to the



user, can easily be used to represent the handles of toolsand can be held in many ways to match the required tool.Unlike force feedback gloves the size of the device is notpartly dependant on the size of the user.

In 1991 a project began at the University of Coloradowith the aim to design and develop a high fidelity hapticinterface [33]. As discussed in section 2 the actuators arean important component in a haptic device which must bedesigned appropriately. For this device maximum forces tobe produced were set at 10 N. To be able to achieve thisforce whilst maintaining low friction a new dry frictionconcept was developed. This requires no seals for containingthe lubricating fluid of previous friction drives and isextremely stiff whilst possessing no backlash or cogging.This device was largely completed in 1999 and over thepast three years the main focus of the research has lookedat how well haptic interfaces can improve the understandingof large complex multidimensional data sets. This deviceuses a parallel mechanism to produce force in five DOF.The haptic interface project is now looking towards anew theme: to investigate how well users can conveythree-dimensional concepts directly in three dimensions.One possible application is to use the haptic interface inconnection with teaching three-dimensional vector calculusconcepts to students.

Another example of a pen based device is the Phantomproduced by SensAble Technologies. There are five devicesavailable in the Phantom range [34]. These devices start withthe Phantom Desktop which has been designed for the officeenvironment. This device has a work area which can be fullyutilized with only hand and wrist movements. It has beenused in a wide variety of applications including art, designand medicine. When tried by the author smooth unimpededmovements can be made and sufficient forces for desktopapplications are applied. The user must take care in notapplying too much force as the limit of the device can beexceeded relatively easily.

Two-dimensional paint programs and design programs arewell established but commercial three-dimensional art pro-grams that use input devices capable of three-dimensionalforce feedback are not commonplace. The Phantom has beenused as the three-dimensional input device capable of forcefeedback in art and design applications that allow painting[35], sculpture [36][37], engraving [38] and carving [39].

DAB [35] is an example of a haptic paint program whichallows the user to paint onto a virtual two-dimensionalcanvas using a virtual three-dimensional paintbrush. ThePhantom Desktop is incorporated to provide the hapticfeedback for this program. The user holds the stylus ofthe device like a paintbrush and the bristles of the brushare modelled such that realistic strokes can be producedunder physical rules. A variety of brushes are simulated toallow a variety of effects to be utilized. Three-dimensional

modelling has also been developed. Freeform [37] producedby SensAble Technologies is one example of a modellingtool using the Phantom. The user is able to interact with adeformable object representing virtual clay. The model isconstructed by modifying a volumetric representation. Thisprogram is used by designers and artists. The designer usesthe stylus to operate a virtual carving tool on the screen.At the University of North Carolina a modelling tool basedon subdivision surfaces has been developed called inTouch[36]. This tool allows a mesh to be modified at severallevels to achieve the desired shape. The user can also paintonto the surface of the object using the haptic device as thepaintbrush.

The Phantom has been incorporated into many medicalapplications. One such application is the examination ofthe human thigh [40]. The system uses a spring dampermodel to represent a deformable human thigh. The datafor the thigh has been obtained using echography and thesystem is used to train practitioners to detect thrombosis inthe vein. The Phantom has also been used as the device toprovide feedback for virtual reality training when diagnosingprostate cancer. The stylus is not used in this example theuser’s index finger is placed in the thimble gimbal [41].Astley and Hayward [42] detail the constraints that needto be adhered to when linking a haptic feedback device tosurgical simulations. They give several techniques which canallow the update rates of the haptic and visual rendering to beachieved. These techniques result due to observations maderegarding the amount of detail and feedback that is required.For instance they suggest that the user is focused on a smallregion of interest when probing a virtual body. The regionof interest can be represented with high detail compared toparts of the object outside of the region of interest.

Phantom Premium is the range of haptic devices whichallow a larger work area and can produce larger forces withsix DOF. There are three devices in the Premium rangeeach with varying size of work area and maximum exertableforce. Ford Motor Company uses a large Phantom for testingthe design of a vehicle. The user is able to feel the interiorof the car. This is a type of virtual prototyping. Virtualprototyping is the process of constructing a prototype of adesign in a virtual environment and is outlined in a paperby Chen at SensAble Technologies [2]. Prototyping in thisway reduces the time taken to construct the model and alsoreduces the need for modifications that may be requiredfurther along the design stage. Chen’s paper describes howthe Phantom Premium 3.0 can be used in virtual prototyping.It describes the range of areas to be product visualisation,fit analysis, dynamic simulation and maintenance analysis.Chen uses the example of the haptic device being integratedwith Boeing’s VPS system for maintenance analysis. In onetest the user is required to move a teapot around simulatedlanding gear. Their tests have shown that haptic feedback isalmost essential in order to make the task possible and thatsix DOF is significantly better in this case when compared



to three DOF. Virtual prototyping can also be performed inadistributed environment; Adidas use SensAble’s devices tohelp design their shoes in a virtual distributed environment[24].

Another six DOF device is the Freedom 6S, commerciallyavailable through MPB Technologies, in association withProf. V. Hayward [43]. This device can produce a maximumforce of 2.5 N and exhibits a resolution in the same leagueas the Phantom Desktop. The Freedom 6S has a largerworkspace when compared to the Phantom Desktop andis being promoted for a variety of applications rangingfrom animation through CAD to telemanipulation. It is theresult of a 14 million dollar project started in 1992 to beused in telerobotic applications. The level of fidelity is veryhigh, so much so that it is claimed that surgeons using thedevice should not be able to feel the difference betweenusing a real scalpel to cut through tissue and using theFreedom 6S to cut through virtual tissue [44]. A six DOFdevice capable of 25 N maximum force has also recentlybecome commercially available. This device is called theDelta Haptic device based on the delta manipulator andwas designed at the Institut de Systemes Robotiques [45].This device also uses a parallel design and has basemounted actuators. These properties help to ensure a highstiffness and a low inertia. Experimental results have provenpromising when testing the device for navigating a mobilerobot through a maze.

Many haptic devices have been applied to and purposelybuilt for medical applications. A device originally designedfor this purpose is the Freedom-7 [5]. This device has sevenDOF and its design allows it to be adapted to simulatescissors, knives and forceps. The original concept for thisdevice was recorded by Hayward in 1995. The work arearelates to an ellipsoidal volume of axis lengths 130× 160×180 mm. The work area is roughly the same as the low rangeof the Phantom Premiums although it has an extra DOF. Thisextra DOF comes from the ability to translate 10 mm relativeto the rest of the device. The extra DOF can be utilized forthe opening and closing of scissors and forceps. When thisextra DOF is not required the device can be optimised touse only six DOF. Two advantages of this device are itssmall footprint ensuring a low visual intrusion and staticbalance. This device is made from aluminium. Research iscurrently being undertaken to see how advanced materialscan be used which could lead to a lighter construction withhigher stiffness and higher structural damping [5].

Minimal invasive surgery is performed very frequentlyas it has advantages for the patient such as faster recovery,less damage to healthy tissue and smaller scars. However,this procedure has its disadvantages for the surgeon. Theseare restricted vision, difficult hand–eye coordination andhandling of instruments with limited mobility. To be ableto train doctors and students more effectively to completethese procedures devices have been constructed such as

the Laparoscopic Impulse Engine. This is a five DOFdevice produced by Immersion Corp. The device is wellsuited to Laparoscopy and Endoscopy procedures with amaximum force of 8 N and an accurate position resolutionof 0.025 mm. It is claimed to bring unprecedented levels ofrealism to surgical simulations. This device has been used inthe Karlsruhe Endoscopic Surgery Trainer [46]. This systemwas developed to aid in the training of minimal invasivesurgical procedures and the first commercial systemwas installed at MIS-training System at the UniversityHospital/Tuebingen Germany in 1996. A rough imitationof the outward human abdomen is utilized in conjunctionwith electromechanical instrument guidance and trackingsystems. A variety of surgical instruments and endoscopiccameras can be imitated. The feedback is provided throughtwo Laparoscopic Impulse Engines. A new device forlaparascopic applications is the Laparoscopic SurgicalWorkstation by Immersion Corp. It provides the forcefeedback to a new training system by Reachin Technologiestitled The Reachin Laparoscopic Trainer [12]. It consistsof a 19” flat panel display controlled by a PC with dual1.8 GHz processors plus graphics card. The trainer will takethe user through several steps of showing an informativevideo, to guiding the user through the procedure beforeallowing them to perform a number of tasks. An importantfeature is the ability to perform skill assessment. This isachieved by recording every movement that the laparoscopicinstruments make. This performance data can be analysed toprovide information regarding errors, any possible damageto patient tissue and variation from the ideal path.

The devices discussed previously consist of rigid materi-als linked together. Another way of manipulating the part ofthe device held by the user is by attaching it to strings or steelcables which can be tightened and relaxed to move a part ina required direction. The advantages of these stringed forcefeedback devices are their low weight and small inertia. Theyalso tend not to intrude in the visual space of the user sinceonly thin cables and a small structure which supports them isrequired. The disadvantage is that the cables can only apply aforce in one direction, if the device needs to move back in theother direction another string and actuator is required. Fora complete device this can mean a large number of stringsand actuators. One such stringed device is called the SpaceInterface Device for Artificial Reality (SPIDAR) [47]. Theoriginal design was a cube with four cables extended fromfour vertices of the cube. At each vertex was an actuator andpulley system capable of applying the forces to the cable.The other end of each cable was attached to a centrepiecewhere the user’s finger was placed. Later the SPIDAR IIwas produced. This device uses eight cables which allowforces to be applied to both one finger and a thumb. Morerecently the Scaleable-SPIDAR has been developed capableof providing greater forces and a much larger workspace.This device is discussed in section 8.



4. Haptic Feedback Gloves

Haptic feedback gloves open up the world of force feedbackby allowing the user to pick up and feel virtual objects ina much more natural way. This ability is required in manyapplications. The first problem in designing a device forproducing force feedback to the hands is the weight of theparts that are needed. The heaviest parts of the device areusually the actuators. These are often placed on the arm orback rather than the hand which can quickly cause fatigue,as well as needing a large amount of space on the hand.

Another concern for the developer is deciding which handmovements to apply force feedback to. Including the wristthe human hand has 26 DOF. To apply force feedback to allthese would require many actuators and additional linkingmaterials that would make the device uncomfortable to wearas well as increasing the price significantly. One way toreduce the problem of weight is to mount the device ontoa desk or wall for support. The University of Tokyo didthis when they produced their glove in 1994 [48]. It is amechanical exoskeleton, which stands on a desk, into whichthe user places their hand. Eleven DOF can be utilized whenoperating this device. The Sensor Glove II, which allowed20 DOF, was developed between 1995–1999.

Most of the early portable feedback devices allowedlimited force feedback, for example the University ofTsukuba’s Hand Master developed in 1992 [7]. It is a simplydesigned string based device which allows force feedbackto the thumb and first finger. In the case of the finger anactuator is placed on the back of the hand which tightensa cable stretched along a beam to a pulley. The cable isattached to the fingertip. In 1993 a design was patented for aglove which had both force and tactile feedback. The tactilefeedback consisted of a three by three array of micropinswhich are positioned at each fingertip. The addition oftactile feedback to the glove allowed texture of objects to beperceived and therefore increased the information the usercan retrieve when touching a virtual object. In 1995 VirtualTechnologies produced the CyberTouch Glove based on thepatent [7]. Virtual Technologies has now been acquired byImmersion Corp. A force feedback glove titled CyberGraspis also produced by Immersion Corp [49]. It is able toproduce 12 N per finger and allows the user the freedom ofa 1 mradius hemisphere for working.

The human–machine Interface Laboratory at RutgersUniversity has a history of producing haptic feedback gloveswith their Rutgers Masters Range. Recently produced isthe Rutgers Master II-New Design (RMII-ND) [50]. Thisglove allows 16 N forces to be exerted onto the thumb,index finger, middle finger and ring finger. It uses pneumaticactuators arranged in a direct drive configuration. Theadvantage of this is the lack of cables and pulleys to promotea more compact and light weight structure. The weightof this device is approximately a third of the weight of

the CyberGrasp discussed above. The disadvantage of thisdevice is that the structure is located near the palm and sothe users’ movement is limited to a certain extent. However,this design does have the advantage of not being able to forcethe user’s fingers backwards.

At the University of Tsukuba a device aimed at allowingtwo hands to experience tactile feedback is being developed.With this device, known as FEELEX, the user is not requiredto wear an array transmitting the feedback but instead anarray of actuators is mounted to a base. Attached to theactuator array is a flexible screen made from rubber witha top layer of white nylon cloth. An image is then projectedstraight onto the cloth from above. The user is then able tolook directly at the image and feel the surface to obtain bothvisual and haptic information. Due to the fact that the user isnot required to wear any equipment several people can usethis system at the same time. There are some limitations withthis system such as the inability to represent a sharp edge andactuator overload caused by too much force being applied bythe user [51].

5. Arm Exoskeleton Haptic Devices

Applications can be envisaged where the workspace andforces provided by devices discussed previously wouldsimply have too many limitations. This leads us to devicesthat allow the user’s arm to experience force feedback. Themost common configurations to achieve this are exoskeletonconstructions.

The user places their arm inside the device and forces canbe applied to separate points along the arm and hand. It isoften the case that separate devices are used for the arm andhand. The force feedback for the hand can be reflected usingone of the gloves discussed in the previous section. With theincrease of the forces involved and the fact that the user isactually inside the device makes safety an important issue.

The Sarcos Dextrous Arm Master, [52], was originallydesigned for underwater telerobotic applications. The armis attached to a base resting on the floor. This device hasten degrees of freedom with 97.7 N-m of torque at theshoulder, 50 N-m at the elbow, 22 N-m at the wrist and5.5 N-m at the hand. High pressure oil is used by theactuators to provide the force feedback but this has thedisadvantage of the risk of oil leaks. The Dextrous armis available for telerobotic applications where a slave isalso supplied to mimic the movements of the master. Afull body suit is also available from Sarcos which allowsthe user to control a humanoid robot or a character in avirtual environment with 32 DOF, however, this suit doesnot provide force feedback. The Sarcos Dextrous ArmMaster has been linked with the Utah’s Alpha1 CADsystem to manipulate virtual mechanisms [54]. Another armmanipulator based on an exoskeleton design is the MasterArm produced at the Southern Methodist University. This is



aunilateral aluminium manipulator grounded to a chair. Thedevice is strapped to the right arm and inflatable cushions areused for force feedback. It is used as part of the PneumaticHaptic Interface which allows the users to feel objects in thecomputer generated environment [56].

One smaller desktop device capable of producing forcefeedback to the whole hand and arm is the CyberForce pro-duced by Immersion Corp [49]. This device is proficient inproducing force feedback to the users arm and in conjunctionwith the CyberGrasp the user can also experience force feed-back to each finger. The workspace is limited to 300 mm by300 mm and a maximum force of 8.8 N can be experiencedmaking this device perfect for the desktop environment. Thisdevice currently retails at approximately 70 000 EUR [14].

Devices, which are grounded on the users body, canprovide an increased freedom to make the experience morenatural. One disadvantage of this is that the user has tosupport the weight of the device. Considerations of weightand expense have probably limited the developments ofportable force feedback devices for the arms. A portablejoystick has been designed at the Univeristy of Tsukuba.This joystick has three degrees of freedom and weighs 500 g.The joystick is strapped to the users’ arm and allows freedomto move around [57]. Some larger force feedback deviceswill be introduced in sections 7 and 8.

6. Workbenches

The connection between the three-dimensional forcefeedback device and the graphics projected on the two-dimensional screen still needs further developments.Problems arise when the user is required to use the devicesome distance from the virtual object. It can requirea prolonged training period in which the user has toget accustomed to moving a three-dimensional objectand watching the interactions a small distance away onthe monitor. If the user could appear to manipulate thethree-dimensional object directly then this would be animprovement.

The Reachin Display has achieved this ability to seeand feel the object in the same place by using a semi-transparent mirror onto which the display from the monitoris projected. CrystalEyes glasses are incorporated to allowthe user to perceive the object in three dimensions [53]. Withthe Reachin system one hand is used for navigation and theother is used to touch the virtual objects. For the navigationa SpaceMouse can be used and for the haptic feedback aPhantom device is used. There are two types of systemthese are called the Desktop Display and the DeveloperDisplay. The Desktop Display uses a Phantom Desktopwhereas the Developer Display uses a Phantom Premium1.5 haptic display. The Reachin display currently starts ata price of approximately 36 000 EUR [14]. Arsenault andWare have conducted experiments using apparatus similar to

the Reachin Display to find out the affects of force feedback,head tracking and correcting the perspective view of thedisplay [58]. Their results showed that the performance ofthe task was improved by 20% when head tracking andforce feedback was used in combination with this apparatus.Another system similar to the Reachin display is the Visual-Haptic Workbench developed at the University of California[59]. This system includes a CRT suspended from the ceilingprojecting onto a mirror beneath. The user looks at themirror wearing CrystalEyes glasses and manipulates theenvironment with two-Phantom devices. A separate deviceis used for the index finger and the thumb of the operator.

Larger examples of this amalgamation of three-dimensional viewing and force feedback are the hapticworkbenches. These types of system usually consistof a virtual reality workbench, glasses and a hapticfeedback device. The workbench and glasses ensurethree-dimensional objects can be perceived and the hapticfeedback device allows objects in the virtual environmentto be felt. In general these devices allow a larger workspacethan the Reachin Display described previously. One of theearly workbenches was the Grope workbench [60]. TheGrope project was started in 1967 with the aim of theproject being to link visual and haptic display for use inresearch regarding molecular docking systems. The projectconsisted of four stages of development, the first stageconcerned a two dimensional system and the final stagecompleted the initial aim, a 6-D molecular docking system.This final system is called the Grope III and consists of anArgonne Arm attached to a Sun4 and uses a large screenfor visual display capable of producing stereovision via aTektronix alternating polarizing plate. The use of this devicein research undertaken by chemists regarding moleculardocking has proved the usefulness of haptics in scientificvisualisation of this nature.

Another workbench is the Nanomanipulator [61]. Thissystem allows the user to interact with an environmentmagnified a billion times. This system was constructedin 1992 when a Scanning Tunnelling Microscope built atUCLA was linked with a Head Mounted display at UNC.An Argonne III remote manipulator was used to provide theforce feedback. The use of the head mounted display allowedthe user to be surrounded by the microscopic environmentwhile touching and modifying the object.

More recently a haptic workbench has been constructedat the University of Utah [55]. The system was constructedto allow research to be carried out into the benefits of hapticscientific visualisation. Their research concerns the use oftheir system for volumetric CT/MRI/MRA data, computa-tional fluid dynamics data and finite element solutions tobioelectric field problems. For the visual display a FakespaceImmersive Workbench is used in combination with Stereo-graphics CrystalEyes LCD shutter glasses. To provide thehaptic feedback a SensAble Phantom 3.0 haptic device is



used and a pinch glove can be operated with the subdominanthand to allow the user to navigate menus.

7. Human-Scale Haptic Devices

Human-scale devices concern those systems that allow theentire human body to be inside the virtual environment.These systems are particularly useful when the applicationrequires an immersive experience with visual and forcefeedback.

At the University of Tsukuba, Hashimoto and Iwatahave undertaken research into using immersive projectiondisplays and haptic feedback [62]. Their system comprisesof a prototype Ensphered Vision display and a HapticMaster.The HapticMaster produces good fidelity of forces but thethree pantograph mechanisms tend to impede the users’motion. The Ensphered vision display consists of a singleprojector and two mirrors allowing a field of view of 360◦horizontal and 125◦ vertical. The movement inside thedisplay is limited due to the static haptic device beingused. The advantage is the large workspace which canbe seen seamlessly and without distortion or perspectiveproblems. This system has been applied to medical dataapplications to allow a user to navigate and interact withComputed Tomography (CT) volume data. The visualdisplay surrounds the user to provide better visual feedbackcompared to the workbenches described in the previoussection but the freedom of motion provided by the hapticdevice is limited to an eight-inch radial dome which insome applications will not be satisfactory. The next deviceto be discussed allows forces to be experienced over a muchlarger workspace.

The device is described as a Safe Large Workspace Hapticdevice produced at Harvard University [63]. The design wasmotivated by the requirement to provide safe, repeatable,accurate and smooth controlled resistance to the user overa large workspace. It is very versatile in its application tosports training and rehabilitation. This is due to the endeffectors ability to accommodate a variety of componentsand objects to grip sports equipment and support the users’body. This device can be used comfortably by a 6ft 4in tallperson when training for a number of sports such as javelinand shotput. The maximum force of 500 N and workspacevolume of a sphere three meters in diameter make this deviceapplicable to natural body movements and strong enoughto support the user. Another device of similar workspacevolume is the Scaleable-SPIDAR. It is a large-scale versionof the SPIDAR, mentioned in section 3.3, which permits theuser to experience force sensations of weight, contact andinertia [64]. The design is similar to the SPIDAR discussedbut this time the user stands inside the cube instead ofjust placing their hand inside. A prototype has been builtto the dimensions of a 3 m cube with a 100-inch displayscreen. The prototype allows finger rings to be worn on

both hands to allow a maximum force of 30 N to be felt.Experiments have been undertaken into how useful thisdesign is in terms of providing haptic feedback to virtualenvironments. These experiments have shown that the forcefeedback provided increases the user’s ability to completethe task. The advantage of this device is the limited intrusioninto the workspace. The weight of the parts of the devicewhich interface with the user is negligible. Problems canarise if you move faster than the motors can reel the cablein, this causes the cable to be suspended under its weightand can provide false information regarding the position ofthe hand. Another disadvantage is that the user is limited tothe size of the cube. The following device also uses a cable toprovide the force feedback but it is a portable device whichgives the user an increased freedom of motion.

This device is being developed at the Research Centrefor Advanced Science and Technology, at the University ofTokyo. The system combines a portable haptic device withimmersive projection displays such as CAVE displays. It isknown as hapticGEAR [65], which consists of a backpack,worn by the user, containing actuators. A wire stretches infront of the user and a pen is attached to the wire to provideforce feedback to the hand. This design ensures that theuser’s visibility is not effected and that most of the weightcan be located on the back which is less likely to tire theuser. A major advantage of this system is the freedom ofmovement and therefore the large workspace which can beexploited. This system has been applied to virtual prototyp-ing such as in manipulating a full size model of a car.

To allow truly immersive experiences the key will be inallowing the user to feel forces on any part of the body whenit collides or touches virtual objects. The previous devicecould possibly be developed to allow cables to be linkedon key joints on the user to apply forces by tightening andreleasing the joints. The current problem is that the actuatorsrequired are still relatively heavy when compared to thepower they can produce. Locating all the actuators requiredfor this type of system on the back would prove too heavyfor the user to carry for any length of time comfortably.The weight of the design has constrained full body forcefeedback devices by grounding them in order to take thepressure off the user.

An early design for a full body haptic display is a non-portable design using an exoskeleton approach. This designwascalled “Immerse” produced by Zechner in 1993 [7]. Thissuit uses a head mounted display for the visual feedback.The problem with this design is the restriction in movement,as the user is not permitted to walk freely. Some researchhas been developed which incorporates an Omni-directionaltreadmill to allow the user to walk around whilst staying ina relatively small area [66]. The device has been developedfor the US Army Dismounted Infantry Training Program.Section 9 includes other locomotion interfaces to allownatural motion.



To allow users to feel as though they are moving over arelatively large distance when in fact they have only moveda fewcentimetres leads us to Motion Platforms.

8. Motion Platforms

Motion platforms allow the user’s whole body to be movedso that they can perceive sensations such as moving quickly,falling and moving over rough terrain without actuallyleaving a small area.

One of the first uses of the motion platform in virtualenvironments was the application to flight training. Manyflight simulators have been constructed to train pilots in avariety of simulated environments. The force feedback isusually provided from actuators located in a base mountedon the floor. The motion platform then sits on top of thebase and actuators. The arrangement of these platformsis often based on designs, by Stewart in 1965 [67]. Thisdesign consists of six actuator arms connected between thebase and the motion platform and was used for early flightsimulators, as well as in some Joysticks such as the HapticMaster [68]. Several types of actuators can be used includinghydraulic, pneumatic, and electrical. The hydraulic actuatorsare probably the best suited to motion platforms, particularlythe large motion platforms, as they are accurate and canproduce large forces. However, the flammable hydraulicfluid pushed through at high pressure has a potential to leak.Pneumatic and electrical techniques used in the PemRammay become commercially viable and should be much safer.

The largest flight simulator is produced by NASA AmesResearch Centre called the Vertical Motion Simulator,VMS [69]. The cab has a range of motion consisting ofseventy feet vertically, 40 feet lateral movement and 8 feetlongitudinal movement. Eight 150 horsepower motors arerequired to move the platform which weighs 70 tons. Thesize of this simulator and the larger range of motion makeit possible to achieve critical conditions such as during takeoff. This device has six DOF to match the degrees of freedomof a real aircraft. The motion platform allows for a variety ofdifferent cabs to be attached to it to simulate a range of craft.These include helicopters, space shuttles and fighter jets.

Motion platform technology is also applied to theentertainment industry. This ranges from single user arcadegames to multi-user theatre simulations in which the entireaudience experiences motion. Universal Studios houses aride based on a roving motion platform called Men In Black– Alien attack [70]. This ride allows the audience to expe-rience forces on the pod in which they sit. These forces areapplied to give the impression of aliens interacting with thepod and the impression of movement at high speed. Singleuser chairs are also available in the entertainment industry.A chair titled the ”R & R chair” provides motion to the userand display when the user moves the joystick. A small aircompressor is used to provide power to the chair [71].

August Designs Inc, have produced a Ship Motion Simu-lator [72]. This is a motion platform similar in configurationto the Stewart Platform. It allows the user to simulate thephysical motion of a variety of boats from small rafts to largecontainer ships as well as wave conditions. They believe thissimulation to be particularly valuable for the training andtesting of personnel and equipment for use on board ships.The surface area of the motion platform measures 4 feet by5 feet and the device is priced at approximately 85 000 EUR.

Alternative devices to the motion platforms developed areheadsets that can be worn which stimulate the area of skinnear to the ear by transmitting signals that affect the usersbalance. By varying the signals produced by these headsetsthe user can be made to feel unbalanced. Virtual Motion hasproduced one such example of a virtual motion headset [73].

9. Locomotion Interfaces

In the previous section devices were discussed which gavethe user the feeling of motion whilst the user stayed in arelatively small area. To simulate more natural movementsthrough larger virtual environments locomotion interfacescan be incorporated. They allow the user to walk througha virtual environment and require energy to do so. Theseinterfaces provide advantages for applications in training andsimulations involving tasks where humans are required tomove naturally through an environment. In particular wherethe users fatigue has an impact on how the simulation is usedas apposed to performing a task whilst sitting in a chair.

The Sarcos Treadport is one example of a locomotiveinterface [74]. The Treadport consists of a 4× 8 ft treadmill,a mechanical tether and a CAVE-like visual display. Themechanical tether is attached to the user which preventsthem from walking through virtual walls. A safety line issuspended from the ceiling preventing the user from fallingif they become unbalanced. Providing the user does notmove too rapidly the system will allow the user to squat andcrawl on their hands and knees. The mechanical tether canprovide force feedback to the user to simulate walking upand down slopes without the need of moving the treadmillto the desired incline. Psychophysical experiments haveshown this approach to be reasonably successful. Currentlythe research undertaken at the University of Utah involvesthe evaluation of the benefits of three dimensional forceapplication to the body.

Another locomotion interface is the Torus Treadmillproduced at the University of Tsukuba [75]. The torustreadmill consists of 12 conveyor belts positioned side byside with 2 mm gaps. Each conveyor belt is driven by an ACmotor to achieve a maximum conveyor speed of 1.2 m/s. Thebelts are moved in the perpendicular direction to the rotationof the belt to allow the user to walk in any desired directionindefinitely. Due to the speed restrictions of the belts the usermay have to walk slower than they would naturally walk.



Table 1: Comparison of Tactile Feedback Devices

Title Developer Year Effect No. of Stimuli

CyberTouch Immersion Corp 1995 0–125 Hz 4 fingers, thumb, palmTractile Device IBM Almaden Research Centre 1999 30 Hz 1Pneumatic Steering Wheel University of British Columbia 2001 10Hz 1 - (8 or more)Lateral Skin Stretch McGill University 2000 - 64 actuator/112 contactor/36 gapFingertip Stimulator University of Exeter 2001 25–400 Hz 100 contactorsTouchMaster Exos, Inc 1993 210–240 Hz 4 fingers, thumbTactool System Xtensory, Inc 1995 Impulsive 30 g 2 fingers

Vibration 20 HzDisplaced Temperature Sensing System CM Research - Temperature 10–35◦C fingerTemperature Display Hokkaido University 1993 Temperature−10–60◦C fingertip

- indicates information not available

Table 2: Comparison of Desktop Haptic Feedback Devices

Title Developer Year DOF Max Force(N)/ Resolution(mm) Workspace(mm)Torque(N-m)

MouseCat Haptic Technologies 1997 2 10 - 125× 75Pantograph McGill University 1993 2 10 - 100× 160PenCat McGill University 1998 3 - - 100× 60× 25Impulse Engine 2000 Immersion Corp 1999 2 8.9 0.02 152× 152Phantom Desktop SensAble Technologies 1993 3 out/6 in 6.4 0.02 160× 130× 130Freedom-7 McGill University 1998 7 5/0.6 0.02 130× 160× 180 7th

dof:10HapticMaster University of Tsukuba 1994 6 17.6/0.54 0.4 sphere Ø400Freedom 6S MPB Technologies 1999 6 2.5/125 0.02 220× 240× 220SPIDAR Tokyo Institute of Technology 1990 3 4 per string 0.5 900× 600× 600SPIDAR II Tokyo Institute of Technology 1994 6 to 12 4 per string 0.5 300Maglev Carnegie Mellon University 1996 6 55/6 0.003 15–20◦ rotation, 25

translationFEELEX 2 University of Tsukuba 2001Screen 10.8 at top of rod 8 50× 50Haptic Interface University of Colorado 1999 5 8 0.005 sphere Ø300Delta Haptic Device Institut de Systemes Robotiques 2001 6 25/0.2 < 0.1 trans< 0.04◦ rot cylinder Ø360× 200Excalibur Haptic Technologies 1999 3 200 0.008 300× 300× 200


The motion of the feet is measured by magnetic sensors.When the displacement is determined the belts can be movedin the opposite direction to cancel out the step. The overallwalkable area of the treadmill is one metre square.

10. Conclusions

This survey is intended to give insight into the types of hapticfeedback device available and some of the applicationsincorporating haptic feedback. The Tables 1–4 allow easycomparison of the lastest force and tactile feedback devices.The most common category of haptic feedback device isthe desktop device. The Phantom devices being the mostcommon to be used in a variety of applications ranging from

sculpture to medical training. A large category of haptics isdevoted to medical applications with a series of specialiseddevices to train users in performing surgical and exploratoryprocedures. Currently the technology is too expensive for thestandard user to purchase their next computer accompaniedby a six degree of freedom haptic feedback device, however,in the near future we should see the force feedback mousebecome a prominent feature in the Windows environment.The addition of the three degrees of freedom desktop devicewill certainly follow.

Towards the high end of the range of haptic feedbackdevices future developments could include the production ofa portable haptic feedback suit which would provide forcefeedback to all parts of the users body in a large scale



Table 3: Comparison of Haptic Feedback Gloves and Arm Exoskeletons

Title Developer Year DOF Max Force(N)/ Workspace(mm)Torque(N-m)

Sensor Glove University of Tokyo 1994 11 - -Sensor Glove 2 University of Tokyo 1998 20 - -Sensor Arm University of Tokyo 1998 7 - -Hand Master University of Tsukuba 1992 2 per finger 7–20 at fingertip Joint Angle 60◦CyberForce Immersion Corp 2001 6 8.8 300× 300CyberGrasp Immersion Corp 1999 5 12 per finger 1000 radiusRMII-ND Rutgers University 2000 4 16 per finger 2000 radiusSarcos Dextrous Arm Master Sarcos 1991 10 97 N-m shoulder 180◦ shoulder

50 N-m elbow 105◦ elbow50 N-m wrist 105◦ × 180◦ × 100◦ wrist5.5 N-m hand 80◦ thumb

Pneumatic Haptic Interface Southern Methodist University 1999 - 854N/28-58 N-m* -

- indicates information not available* operating at 100psi

Table 4: Comparison of Large-Scale Haptic Devices

Title Developer Year DOF Max Force(N)/ Resolution(mm) Workspace(mm)Torque(N-m)

hapticGEAR University of Tokyo 2001 3 15.7 10 Portable (Back grounded)WearableMaster University of Tsukuba - 3 1.9 - Portable (Arm grounded)Scaleable-SPIDAR Tokyo Institute of Technology 2000 6 15 3000× 3000× 3000HapticMaster FCS Control Systems 2000 3 250 < 0.004 1 rad, 280–360 radius, 400 heightLarge Haptic Device Harvard University 1996 6 500/550 - sphere Ø3000


workspace. This idea seems a very exciting prospect withapplications in training for a variety of purposes includingmilitary as well as fully immersive meetings in virtualdistributed environments. The current limitations of actuatortechnologies prevent this design from becoming a reality atthe present time.

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Recent Developments and Applications of Haptic Devices