Robotic Engineering Project1.IntroductionAn industrial robot is defined by ISO as an automatically controlled, reprogrammable, multipurpose manipulator programmable in three or more axes. The field of robotics may be more practically defined as the study, design and use of robot systems for manufacturing (a top-level definition relying on the prior definition of robot).

Typical applications of robots include welding, painting, assembly, pick and place, product inspection, and testing; all accomplished with high endurance, speed, and precision.

1.1. Short history 1954: The first programmable robot is designed by George Devol. He coins the term Universal

Automation.

1956: Devol and engineer Joseph Engelberger form the world's first robot company, Unimation.

1960: Unimation is purchased by Condec Corporation and development of Unimate Robot Systems begins. American Machine and Foundry, later known as AMF Corporation, markets a robot, called the Versatran, designed by Harry Johnson and Veljko Milenkovic.

1962: The first industrial robot was online in a General Motors automobile factory in New Jersey. It was Devol and Engelberger's UNIMATE. It performed spot welding and extracted die castings.

1973: German robotics company, KUKA, creates the first industrial robot with six electromechanically-driven axes. It is called the Famulus.

1974: A robotic arm (the Silver Arm) that performed small-parts assembly using feedback from touch and pressure sensors was designed. Professor Scheinman, the developer of the Stanford Arm, forms Vicarm Inc. to market a version of the arm for industrial applications. The new arm is controlled by a minicomputer.

1978: Vicarm, Unimation creates the PUMA (Programmable Universal Machine for Assembly) robot with support from General Motors. Many research labs still use this assembly robot.

1979: Nachi developed the first motor-driven robots for spot welding.

1987: ASEA of Vasteras, Sweden (founded 1883) and BBC Brown Boveri Ltd of Baden, Switzerland, (founded 1891) announce plans to form ABB Asea Brown Boveri Ltd., headquartered in Zurich, Switzerland. Each parent will hold 50 percent of the new company.

1988: The Motoman ERC control system was introduced with the ability to control up to 12 axes, more than any other controller at the time.

1992: FANUC Robot School was established.

1994: The Motoman MRC control system was introduced with the ability to control up to 21 axes. It could also synchronize the motions of two robots.

1998: The introduction of the XRC controller allowed the control of up to 27 axes and the synchronized control of three to four robots.

2003: OTC DAIHEN introduced the Almega AX series, a line of arc welding and handling robots. The AX series robots integrate seamlessly with the OTC D series welding power supplies for advanced control capabilities.

1.2. Types of RobotsCartesian robot / Gantry robot: Used for pick and place work, application of sealant, assembly operations, handling machine tools and arc welding. It's a robot whose arm has three prismatic joints, whose axes are coincident with a Cartesian coordinator.

Cylindrical robot: Used for assembly operations, handling at machine tools, spot welding, and handling at diecasting machines. It's a robot whose axes form a cylindrical coordinate system.

Spherical robot / Polar robot (such as the Unimate): Used for handling at machine tools, spot welding, diecasting, fettling machines, gas welding and arc welding. It's a robot whose axes form a polar coordinate system.

SCARA robot: Used for pick and place work, application of sealant, assembly operations and handling machine tools. This robot features two parallel rotary joints to provide compliance in a plane.

Articulated robot: Used for assembly operations, diecasting, fettling machines, gas welding, arc welding and spray painting. It's a robot whose arm has at least three rotary joints.

Parallel robot: One use is a mobile platform handling cockpit flight simulators. It's a robot whose arms have concurrent prismatic or rotary joints.

Anthropomorphic robot: Similar to the robotic hand Luke Skywalker receives at the end of The Empire Strikes Back. It is shaped in a way that resembles a human hand, i.e. with independent fingers and thumbs.

1.3. TerminologyArticulated Robot: An articulated robot is one which uses rotary joints to access its work space. Usually the joints are arranged in a “chain”, so that one joint supports another further in the chain.

Continuous Path: A control scheme whereby the inputs or commands specify every point along a desired path of motion. The path is controlled by the coordinated motion of the manipulator joints.

Degrees Of Freedom (DOF): The number of independent motions in which the end effector can move, defined by the number of axes of motion of the manipulator.

Gripper: A device for grasping or holding, attached to the free end of the last manipulator link; also called the robot’s hand or end-effector.

Payload: The maximum payload is the amount of weight carried by the robot manipulator at reduced speed while maintaining rated precision. Nominal payload is measured at maximum speed while maintaining rated precision. These ratings are highly dependent on the size and shape of the payload.

Pick And Place Cycle: Pick and place Cycle is the time, in seconds, to execute the following motion sequence: Move down one inch, grasp a rated payload; move up one inch; move across twelve inches; move down one inch; ungrasp; move up one inch; and return to start location.

Reach: The maximum horizontal distance from the center of the robot base to the end of its wrist.

Accuracy: The difference between the point that a robot is trying to achieve and the actual resultant position. Absolute accuracy is the difference between a point instructed by the robot control system and the point actually achieved by the manipulator arm, while repeatability is the cycle-to-cycle variation of the manipulator arm when aimed at the same point.

Repeatability: The ability of a system or mechanism to repeat the same motion or achieve the same points when presented with the same control signals. The cycle-to-cycle error of a system when trying to perform a specific task

Resolution: The smallest increment of motion or distance that can be detected or controlled by the control system of a mechanism. The resolution of any joint is a function of encoder pulses per revolution and drive ratio, and dependent on the distance between the tool center point and the joint axis.

Robot Program: A robot communication program for IBM and compatible personal computers. Provides terminal emulation and utility functions. This program can record all of the user memory, and some of the system memory to disk files.

Maximum Speed: The compounded maximum speed of the tip of a robot moving at full extension with all joints moving simultaneously in complimentary directions. This speed is the theoretical maximum and should under no circumstances be used to estimate cycle time for a particular application. A better measure of real world speed is the standard twelve inch pick and place cycle time. For critical applications, the best indicator of achievable cycle time is a physical simulation.

Servo Controlled: Controlled by a driving signal which is determined by the error between the mechanism's present position and the desired output position.

Via Point: A point through which the robot's tool should pass without stopping; via points are programmed in order to move beyond obstacles or to bring the arm into a lower inertia posture for part of the motion.

Work Envelope: A three-dimensional shape that defines the boundaries that the robot manipulator can reach; also known as reach envelope.

1.4. Defining Parameters Number of axes – two axes are required to reach any point in a plane; three axes are

required to reach any point in space. To fully control the orientation of the end of the arm (i.e. the wrist) three more axes (yaw, pitch, and roll) are required. Some designs (e.g. the SCARA robot) trade limitations in motion possibilities for cost, speed, and accuracy.

Degrees of freedom - this is usually the same as the number of axes. Working envelope – the region of space a robot can reach. Kinematics – the actual arrangement of rigid members and joints in the robot, which

determines the robot's possible motions. Classes of robot kinematics include articulated, cartesian, parallel and SCARA.

Carrying capacity or payload – how much weight a robot can lift. Speed – how fast the robot can position the end of its arm. This may be defined in terms of

the angular or linear speed of each axis or as a compound speed i.e. the speed of the end of the arm when all axes are moving.

Acceleration - how quickly an axis can accelerate. Since this is a limiting factor a robot may not be able to reach its specified maximum speed for movements over a short distance or a complex path requiring frequent changes of direction.

Accuracy – how closely a robot can reach a commanded position. When the absolute position of the robot is measured and compared to the commanded position the error is a measure of accuracy. Accuracy can be improved with external sensing for example a vision system or Infra-Red. See robot calibration. Accuracy can vary with speed and position within the working envelope and with payload (see compliance).

Repeatability - how well the robot will return to a programmed position. This is not the same as accuracy. It may be that when told to go to a certain X-Y-Z position that it gets only to within 1 mm of that position. This would be its accuracy which may be improved by calibration. But if that position is taught into controller memory and each time it is sent there it returns to within 0.1mm of the taught position then the repeatability will be within 0.1mm

1.5. ComponentsThe basic components of an industrial robot are the

the manipulator, which is the robot’s arm, consists of segments jointed together with axes capable of motion in various directions allowing the robot to perform work.

the end effector (which is the part of the manipulator). which is a gripper tool, a special device, or fixture attached to the robot’s arm, actually performs the work.

the power suplly provides and regulates the energy that is converted to motion by the robot actuator, and it may be either electric, pneumatic, or hydraulic.

the controller initiates, terminates, and coordinates the motion of sequences of a robot. Also it accepts the necessary inputs to the robot and provides the outputs to interface with the outside world.

1.6. Major robotics companies1.6.1.KUKAKUKA is a German manufacturer of industrial robots and solutions for factory automation. The KUKA Robotics Corporation has 25 subsidiaries worldwide, mostly sales and service subsidiaries, including in the United States, Canada, Mexico, Brazil, China, Japan, Korea, Taiwan, India, Russia and most European countries. The company name, KUKA, is an acronym for Keller und Knappich Augsburg.

The company was founded in 1898 in Augsburg, Germany, by Johann Josef Keller and Jacob Knappich. At first, the company focused on house and street lights, but soon expanded to other products (welding equipment and solutions; big containers), to become the market leader in communal vehicles in Europe by 1966. Keller & Knappich GmbH merged with part of Industrie-Werke Karlsruhe AG to become Industrie-Werke Karlsruhe Augsburg Aktiengesellschaft, eventually KUKA for short.

In 1973, KUKA created its own industrial robot FAMULUS. At this time, the company belonged to the Quandt group. However, in 1980, the Quandt family withdrew and a publicly owned firm was established. In 1995, the company was split into KUKA Robotics Corporation and KUKA Schweißanlagen (now KUKA Systems), now both subsidiaries of KUKA AG. Today, KUKA concentrates on solutions for the automation of industrial manufacturing processes.

Most robots are finished in "KUKA Orange" (the official corporate color) or black.

The company headquarters are located in Augsburg, Germany. As of September 30, 2012, KUKA employed more than 3,150 workers. While previously emphasizing customers in the automotive industry, the company has since expanded to other industries.

Notable milestones

1971 – Europe’s first welding transfer line built for Daimler-Benz. 1973 – The world’s first industrial robot with six electromechanically driven axes, known as

AMULUS. 1976 – IR 6/60 – A completely new robot type with six electromechanically driven axes and

an offset wrist. 1989 – A new generation of industrial robots is developed – brushless drive motors for a low

maintenance and a higher technical availability. 2007 – KUKA Titan – at the time, the biggest and strongest industrial robot with six axes,

entered into the Guinness Book of World Records. 2010 – As the only robot family, the robot series KR QUANTEC completely covers the load

range of 90 up to 300 kg with a reach of up to 3100 mm for the first time. 2012 – The new small robot series KR AGILUS is launched. 2014 – On February 9, the company uploaded a video on its official Youtube channel

KukaRobotGroup, teasing the audience with their new KUKA robot, specialized in Table Tennis. The teaser video shows a trailer of KUKA's robot initiating fight against a human in Table Tennis. The human is Timo Boll, legend in Table Tennis. This new robot is described as KUKA KR AGILUS, Fastest Robot on Earth. The full video was available on March 10, 2014.

1.6.2.ABBABB is a multinational corporation headquartered in Zurich, Switzerland, operating in robotics and mainly in the power and automation technology areas. It ranked 158th in the Forbes Ranking (2013).

ABB is one of the largest engineering companies as well as one of the largest conglomerates in the world. ABB has operations in around 100 countries, with approximately 150,000 employees in November 2013,[4] and reported global revenue of $40 billion for 2011.

ABB resulted from the 1988 merger of the Swedish corporation Allmänna Svenska Elektriska Aktiebolaget (ASEA) and the Swiss company Brown, Boveri & Cie (BBC); the latter had absorbed the Maschinenfabrik Oerlikon in 1967. CEO at the time of the merger was the former CEO of ASEA, Percy Barnevik, who ran the company until 1996.

ABB's history goes back to the late 19th century. ASEA was incorporated by Ludwig Fredholm in 1883 and Brown, Boveri & Cie (BBC) was formed in 1891 in Baden, Switzerland, by Charles Eugene Lancelot Brown and Walter Boveri as a Swiss group of electrical companies producing AC and DC motors, generators, steam turbines and transformers.

Allmänna Svenska Elektriska Aktiebolaget was a Swedish industry company. It merged with the Swiss Brown, Boveri & Cie (BBC) in 1988 to form Asea Brown Boveri. ASEA still exists, but only as a holding company owning 50% of the ABB Group.

ASEA logo used from the late nineteenth century until 1933

ASEA was founded 1883 by Ludvig Fredholm in Stockholm as manufacturer of electrical light and generators. By a merging with Wenström's & Granström's Electrical Power Company (Wenströms & Granströms Elektriska Kraftbolag)

1889 - the partner Jonas Wenström creates 3-phased generators, motors and transformers. 1933 - The company removes the swastika from the logotype, due to the symbol's

association with Nazi Germany. 1953 - ASEA creates the first industrial diamonds. 1954 - HVDC Gotland project, first static high-voltage DC system 1960s - ASEA builds 9 of 12 nuclear plants in Sweden. 1974 - Industrial robots are introduced by ASEA 1987 - Acquires Finnish Oy Strömberg Ab 1988 - Merges with BBC Brown Boveri

Brown, Boveri & Cie (BBC) was a Swiss group of electrical engineering companies. Brown, Boveri synchronous motor of 1901 in the Électropolis museum of Mulhouse, France

It was founded in Baden, Switzerland, in 1891 by Charles Eugene Lancelot Brown and Walter Boveri who worked at the Maschinenfabrik Oerlikon. In 1970 BBC took over the Maschinenfabrik Oerlikon. In 1988 it merged with ASEA to form ABB.

The company produced DC Motors, AC motors, generators, steam turbines, gas turbines, transformers and the electrical equipment of locomotives. Some of BBC's technology went into German U-boats of World War II, such as the depth controls.

1.6.3.MotomanFounded in 1989, Yaskawa Motoman is a leading robotics company in the Americas. With nearly 300,000 Motoman robots, 10 million servos and 18 million inverter drives installed globally, Yaskawa provides automation products and solutions for virtually every industry and robotic application; including arc welding, assembly, coating, dispensing, material handling, material cutting, material removal, packaging, palletizing and spot welding.

Our product line includes more than 175 distinct robot models and a full-line of pre-engineered "World" solutions that are complete application specific work cells, including robot, process and safety equipment.

Combined with our sister and partner companies, we support robotic solutions throughout the world. Our proven track record of delivering industry leading quality, innovation and customer satisfaction can help you exceed your robotic automation goals.

Yaskawa Motoman is backed by a powerful parent, Yaskawa Electric Corporation of Japan. Since 1915, Yaskawa Electric has demonstrated a passion for automation by developing specialized solutions to help customers increase efficiency, improve quality, boost productivity, and deliver outstanding ROI. As one of the world's largest manufacturers of industrial robots, Yaskawa Electric has offices in 28 countries and approximately 14,000 employees worldwide.

Our sister division, Yaskawa America, Inc., Drives & Motion Division, is a manufacturer of various control products, AC servo motors and drives, and inverters.

1.6.4.FanucFANUC is a group of companies, principally FANUC Corporation of Japan, Fanuc America Corporation of Rochester Hills, Michigan, USA, and FANUC Robotics Europe SA of Luxembourg, that provide automation products and services such as robotics and computer numerical control systems. FANUC is one of the largest makers of industrial robots in the world. It is part of the Furukawa Group. FANUC had its beginnings as part of Fujitsu developing early numerical control (NC) and servo systems. The company name is an acronym for Factory automation numerical control.

In 1972, the Computing Control Division became independent and FANUC Ltd was established.

FANUC Robotics Europe S.A., a sister company, is headquartered in Luxembourg, with customers in Europe, and which provides sales, service and support in Europe and abroad.

FANUC Robotics America Corporation (1992-2013) supplied robotic automation in North and South America, with over 240,000 robots installed. It also produced software, controls, and vision products that aid in the development of robotic systems. Headquartered in Rochester Hills, Michigan, the company had 10 regional locations in the U.S., Canada, Mexico and Brazil. The company provided these systems for applications including automotive and fabricated metals to medical devices and plastics. It was founded in 1982 as a joint venture between FANUC Ltd and General Motors Corporation, named GMFanuc Robotics Corporation. A staff of 70 began work at the GM Technical Center in Warren, Michigan. In 1992, the company became a wholly owned subsidiary of FANUC Ltd of Oshino-mura, Japan. The company was a member of the Robotics Industries Association (RIA) and of the International Federation of Robotics (IFR).

1.6.5.ComauComau (COnsorzio MAcchine Utensili) is an Italian multinational company based in Turin, Italy and is part of the Fiat Group. Comau is an integrated company, including 20 companies, which develops and produces process automation, manufacturing and service solutions and specializes in welding robots. Established in 1973, it currently has 23 different operative centers, 15 manufacturing plants, and 3 research and development centers throughout the world. It employs more than 14,500 people in 13 different countries – Italy, Russia, China, India, Argentina, Mexico, Brazil, Romania, Poland, Germany, France, the United States and the United Kingdom. The company has more than 100 patents and all major automotive manufacturers use Comau systems and machinery at facilities in Europe, America and Asia.

2. Choosing the robot and the wrist mechanism2.1 The robot

The robot I choose for this project is KUKA KR 10 R1100 SIXX WP (KR AGILUS) (http://www.kuka-robotics.com/usa/en/products/industrial_robots/small_robots/kr10_r1100_sixx_wp/) from the class of small robots from KUKA. Thanks to new waterproofing, the KR AGILUS is also right at home under intensive outdoor production conditions. Stable stainless steel covers have replaced plastic parts, and resistant surface treatments and additional seals in the interior of the six-axis robot enable it to be used in a machine tool environment, for example. The waterproof version of the KUKA small robot complies with the higher protection rating IP67.

The main operation performed by this robot should be handling (loading and unloading)

Technical specifications

LoadsPayload 10 kg

Working envelopeMax. reach 1101 mm

Other data and variantsNumber of axes 6

Repeatability <±0,03 mm

Weight 54 kg

Mounting positions

Floor, Ceiling, Wall

Controller KR C4 compact

Protection class IP 67

Sound level < 70 dB (A) outside the working envelope

Axis Range of motion, software limited

Speed with rated payload

Acceleration with rated payload

1 +/-170° 300 °/s2 +45° to -190° 225 °/s3 +156° to -

120°225 °/s

4 +/-185° 381 °/s 800 °/s2

5 +/-120° 311 °/s 700 °/s2

6 +/-350° 492 °/s 1000°/s2

Payloads

Rated payload 5 kgMax. payload 10 kgDistance of the load center of gravity

Lxy 100 mm

Distance of the load center of gravity

Lz 80 mm

Max. total load 10 kg

Foundation Data

Type of load Force/torque/massNormal operation Maximum load

Fv= vertical force Fvmax= 967 N Fvmax= 1297 NFh= horizontal force Fhmax= 1223 N Fhmax= 1362 NMk= tilting moment Mkmax= 788 Nm Mkmax= 1152 NmMr= torque Mrmax = 367 Nm Mrmax = 880 NmTotal mass for load acting on the foundation

KR 10 R1100 sixx WP: 66 kg

Robot KR 10 R1100 sixx WP: 56 kgTotal load for foundation load (suppl. Load on arm+ rated payload)

KR 10 R1100 sixx WP: 10 kg

2.2 Wrist mechanismA robot manipulator needs at least 6 degrees of freedom to manipulate an object freely in space. Typically, the lengths of the first three moving links are much longer than those of the last three

links. An end effector is attached to the last moving link for grasping or fine manipulation of an object. Thus the first three moving links are used primarily for manipulating the position, while the last three links are used for controlling the orientation of the end effector. For this reason, the subassembly associated with the first three moving links is called the arm, and the subassembly associated with the last three moving links is called the wrist. Furthermore, the last three joint axes are often designed to intersect at a common point called the wrist center. The arm delivers the wrist center anywhere in its primary workspace, while the wrist controls the orientation of the end effector.

Theoretically, we can mount one motor with a proper gear reduction unit on each link to drive the joints. This kind of arrangement. however, requires the motors and their gear reduction units to be located close to the wrist subassembly, which will inevitably increase the inertia load to the motors of the arm subassembly. Therefore, it is highly desirable to incorporate some kind of mechanical transmission mechanisms, which allow the actuators to be installed away from the wrist center. In practice, a good wrist design should possess the following characteristics:

1. Three degrees of freedom 2. Spherical motion 3. Large workspace (i.e., large angular orientation range) 4. Remote drive capability 5. Compact size, light weight, and low inertia 6. High accuracy and repeatability 7. High mechanical stiffness 8. Low manufacturing cost 9. Rugged and reliable design

The development of wrist mechanisms can be dated back to the early nineteenth century. It is related especially to the needs in handling nuclear materials, in space exploration, and for other hazardous tasks. To achieve the necessary characteristics, mechanical transmission mechanisms such as epicyclic gear trains, push-rod linkages, and tendon drives are often employed

Epicyclic gear drives are commonly used for speed reduction and torque amplification in mechanical systems. Bevel-gear wrist mechanisms have been incorporated in most industrial robots because they are comparatively simple and compact in size, can be sealed in a metallic housing that keeps the gear trains free of contamination, and can be produced economically and reliably. Furthermore, using bevel gear trains for power transmission, actuators can be mounted remotely on the forearm, thereby reducing the weight and inertia of a robot manipulator.

Proposed solutions

2.2.1. Spherical wrist mechanism

2.2.2. Orthogonal wrist mechanism 1

2.2.3. Orthogonal wrist mechanism 2

2.2.4 Synchronous belts wrist mechanismA wrist mechanism of an industrial robot is provided with a forearm, a wrist base mounted on the forearm so as to be rotatable about a lengthwise rotary axis of the forearm, a wrist body mounted on the wrist base so as to be swingable about a swing axis perpendicularly crossing the rotary axis of the wrist base, and a wrist top mounted on the wrist body so as to be rotatable about an axis perpendicular to the swing axis of the wrist body. The wrist base is characterized in that a motor for rotating the wrist tip and a motor for swinging the wrist body are arranged opposite to each other in a lengthwise direction.

This invention relates to a structure for miniaturizing a wrist of an industrial robot.

FIG. 7 is a schematic diagram of a conventional industrial robot. This industrial robot generally makes motions similar to ones of portions of a human body from the shoulder to the wrist.

In FIG. 7, a shoulder 2 is provided rotatably on a base 1. An upper arm 3 is mounted swingably on the free end portion of this shoulder. A forearm 4 is provided at the free end portion of the upper arm 3 so that the forearm 4 can swing with respect to the upper arm 3. The forearm 4 is driven via a forearm driving motor (no shown), a lever 47 and a driving link 48. A wrist base 5 is provided on a front portion of the forearm 4 so that the wrist base 5 can rotate around the longitudinal axis of the forearm 4. A wrist body 6 is provided on a front portion of the wrist base 5 so that the wrist body 6 can swing around a pivot extending at right angles to the axis around which the wrist base 5 rotates. A wrist tip 7 is provided on a front portion of the wrist body 6 so that the wrist tip 7 can be rotated around an axis extending at right angles to the wrist body-swinging pivot. Various kinds of instruments 8, such as a tool, a welding torch or a handling device are attached to the wrist tip to carry out various machining and processing operations. The above description is of the construction

of a commonly used wrist of an industrial robot. There is also a wrist of an industrial robot, the construction of which is partially different from that of the abovementioned industrial robot wrist. For example, the wrist base-rotating axis, wrist body-swinging axis and wrist tip-rotating axis referred to in the above statement extend at substantially right angles. The angles of these axis do not necessarily cross each other at right angles and they can be regulated in accordance with the working posture.

Japanese Patent Laid-Open No. 59390/1984 discloses a construction of a conventional industrial robot wrist, as discussed above. According to the technique disclosed in this publication, motors for rotating a wrist tip and swinging a wrist body and reduction gears are provided within a wrist base so that this wrist can also be applied to a small-sized industrial robot.

According to the prior art disclosed in the above publication, however, the two motors in the wrist base are parallel-arranged so that each of them orients at right angles to the lengthwise axis of the wrist. Therefore, it is difficult to miniaturize a wrist which generally has an elongated structure of a columnar shape.

If these two motors are arranged so that they extend in the lengthwise direction of the wrist, the following problems which must be solved arise. (1) The transmitting of a driving force from a motor to a tip portion of the wrist is generally done by a belt (including a chain), which is generally extended in the lengthwise direction of the wrist in view of the necessity of miniaturizing the wrist. If these motors are arranged in this manner, it becomes necessary that the driving force from the lengthwise-arranged motors be transmitted to the belts after the direction of the driving force has been changed at right angles, so that the length of the driving force transmitting path increases. If the driving force transmitting path increases, the path along which an external force imparted to the tool at the free end of the wrist tip is transmitted also increases. This would cause the wrist to be displaced accordingly with ease, i.e., the rigidity thereof decreases. (2) If the two motors are arranged in the lengthwise direction of the wrist with no sufficient space left between the rear ends of the two motors and structural members of the wrist facing the rear ends, it becomes troublesome to take out the motors when the maintenance work for the wrist is carried out. Since the output shaft of a motor is generally meshed with a gear, the motor must be taken out by moving the motor in the axial direction thereof. However, when the length of the wrist is not set so large, the motor cannot be moved axially. In such a case, it is necessary that the motor be taken out by moving it in a direction perpendicular to the lengthwise axis thereof. This makes it necessary to disassemble the gear box meshed with the output shaft of this motor, so that the motor-removing operation becomes troublesome. Summary of the Invention

An object of the present invention is to provide an industrial robot capable of being miniaturized by arranging a wrist tip-rotating motor and a wrist body-swinging motor in the lengthwise direction of the wrist, preventing a decrease in the rigidity of the wrist, and carrying out the maintenance work therefor with ease.

A wrist mechanism of an industrial robot according to the invention comprises a forearm, a wrist base provided rotatably around a lengthwise axis of the forearm, a wrist body provided swingably around a pivot or shaft (swing shaft) disposed perpendicularly to the lengthwise axis of the wrist base, a wrist tip portion provided rotatably around a rotary shaft perpendicular to the swing shaft around which the wrist body is swung, and the wrist base has a motor for rotating the rotary shaft and a motor for driving the swing shaft to cause the wrist body to swing around the swing shaft, those two motors being arranged opposite to each other in a lengthwise direction thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an embodiment of a wrist of an industrial robot according to the present invention;

FIG. 2 is a sectional view, which continues from FIG. 1, of the forearm joined to the wrist of the robot;

FIG. 3 is a sectioned side elevation of what is shown in FIG. 1;

FIG. 4 is a sectional view for explaining an operation of the portion of the wrist which is shown in FIG. 3;

FIG. 5 is a sectional view of another embodiment of a wrist according to the present invention;

FIG. 6 is a sectional view of a part of a wrist according to another embodiment of the present invention; and

FIG. 7 is a diagram of the arm as a whole of a conventional industrial robot.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will now be described with reference to FIGS. 1-4. FIGS. 1 and 2 constitute one drawing. An example of an industrial robot comprises a base, a shoulder rotatably mounted on the base, an upper arm swingably mounted on the shoulder, a forearm swingably mounted on the upper arm and a wrist mechanism rotatably mounted on a free end portion of the forearm. The base, shoulder, upper arm and forearm corresponds to ones of the conventional industrial robot shown in FIG. 7, respectively. The wrist mechanism is installed with various kinds of tools to carry out various operation. The wrist mechanism comprises a wrist base 5 rotatably mounted on the forearm 4 around a lengthwise axis of the forearm 4, a wrist body 6 swingably mounted on the wrist base 5, and a wrist tip 7 rotatably mounted on the wrist body 6. The robot carries out various operation with the wrist tip 7 being installed with a tool. The forearm 4 shown in FIG. 2 is supported on an upper arm as shown in FIG. 7 by reference number 3 via a fulcrum 41a. The axial force of a driving link as shown in FIG. 7 by reference numeral 48 is transmitted to a fulcrum 41b, and the forearm 4 is swung around the fulcrum 41a. The rear portion of the wrist base 5 is housed rotatably in the interior of the forearm 4. The rear portion of this wrist base 5 is formed cylindrically and supported on a rotation supporting bearing 42 provided in the forearm 4. A gear 45 on the side of a motor 44 for rotation is meshed with a gear 43 formed on the rear end portion of the wrist base 5. The gear 45 on the side of the rotation motor 44 is connected to the same motor 44 via a harmonic final reduction gear 46.

A method of transmitting power to the wrist body 6, which is provided swingably with respect to the wrist base 5, will now be described with reference to FIG. 1. A motor 61 for swinging the wrist body 6 (referred to as swing motor) is provided in the interior of the wrist base 5 so as to extend in the lengthwise direction thereof. An output shaft 62 of the swing motor 61 faces in the forward direction, and is provided with a bevel gear 63 at the free end portion thereof. A bevel gear 65 is also mounted on a first transmission shaft 64 which extends at right angles to this output shaft 62, and these two shafts 62, 64 are connected at right angles via the bevel gears 63, 65. A pulley 66 is mounted on the other end portion of the first transmission shaft 64, and a belt 67 is engaged with this pulley 66. This belt 67 runs in the lengthwise direction of the wrist base, and is engaged with an opposite pulley 68. This pulley 68 is mounted on a swing shaft 69 around which swing is effected, which shaft is supported on a bearing 52 provided in a housing 51 of the wrist base 5. A harmonic final reduction gear 601 is connected with this shaft 69, and the wrist body 6 is supported on a shaft support bearing 53 via this reduction gear so that the wrist body can be swung. The axis of this shaft 69 extends at right angles to the axis around which the wrist base 5 is turned.

A method of transmitting power to the wrist tip 7 which is provided rotatably with respect to the wrist body 6 will now be described. A rotation motor 71 for rotating the wrist tip 7 is provided in opposition to the swing motor 61 in the wrist base 5 so as to extend in the lengthwise direction thereof. An output shaft 72 of this motor 71 has at its free end portion a bevel gear 73 meshed with a bevel gear 75 mounted on a second transmission shaft 74 which extends at right angles to the output shaft 72, and these two shafts 72, 74 are connected to each other at right angles. The second transmission shaft 74 is provided at the other end portion thereof with a pulley 76 with which a belt 77 is engaged. The belt 77 runs in parallel with the above-mentioned belt 67 in the forward direction in the interior of the wrist base 5. A pulley 78, the other pulley around which this belt 77 is passed, is mounted on a third transmission shaft 79. This third transmission shaft 79 is positioned in parallel with the second transmission shaft 74. The third transmission shaft 79 is provided at its inner end portion with a bevel gear 701, which is meshed with a bevel gear 703 mounted on a rotary shaft 702. The two shafts 79, 702 extend at right angles to each other. The wrist tip 7 is mounted on the front end portion of the rotary shaft 702 via a harmonic final reduction gear 704. The wrist tip 7 is supported on a rotary movement supporting bearing 705 and rotated.

The axes of the shaft 69 and third transmission shaft 79 are aligned with each other, and these aligned axes and the axis of the rotary shaft 702 cross at right angles. The axes of the first and second transmission shafts 64, 74 are also aligned with each other, and a gear box 10, which is described later, can be turned around these aligned axes.

The two output shafts 62, 72, two transmission shafts 64, 74 and bevel gears 63, 65, 73, 75 mounted on these output shafts are housed in the single gear box 10, which can be turned with respect to a bearing housing 101 for the first and second transmission shafts 64, 74. The turning movement of the gear box 10 is normally prevented by a motor holder 104 as shown in FIG. 3. The turning of the gear box 10 is done so as to carry out a maintenance inspection operation easily. The gear box 10 is provided with an opening 102 through which the output shafts 62, 72 of the motors extend. This opening 102 is made so large that the bevel gears 63, 73 mounted on the free end portions of the output shafts 62, 72 can be passed therethrough.

The operation of this embodiment will now be described briefly. When the rotation driving motor 44 is energized, the wrist base 5 is turned with respect to the forearm 4. This turning movement is made around the lengthwise axis of the forearm 4. When the swing motor 61 is energized as the wrist base 5 is turned, the wrist body 6 is swung. This swinging movement is made around the shaft 69, which extends at right angles to the axis around which the wrist base is turned. When the motor 71 is energized as the wrist body 6 is swung, the wrist tip 7 is rotated. Accordingly, the wrist of this industrial robot has three degrees of freedom. A tool is attached to the free end of this wrist tip, whereby machining and processing operations are carried out.

The maintenance work will now be described. FIG. 3 is a side elevation of what is shown in FIG. 1, and FIG. 4 illustrates an operation of the portion of the embodiment which is shown in FIG. 3. When it is necessary to take out the two motors 61, 71 during a maintenance operation, a cover 103 for the wrist base 5 is removed first, and then the motor holder 104, the gear box 10 being then turned around the bearing housing 101. The gear box 10 is turned with the two motor 61, 71 fixed thereto. This turning movement is made around the aligned axes of the first and second transmission shafts 64, 74.

During this time, relative movement occurs between the bevel gears 63, 65; 73, 75 which are meshed with each other. Since brakes are generally provided in these two motors 61, 71, relative rotating movements occur in the free bevel gear 65, 75 positioned on the driven side. Since the angles of such

rotating movements of the bevel gears are not more than 90°, and since the speeds of the same movements are reduced (to, for example, around 1/50-1/100) by the harmonic final reduction gears 601, 704 installed at the terminal ends on the power transmission paths, the angles of rotating movement of the wrist body 6 and wrist tip 7 constituting driven members are very small, i.e., the wrist body 6 and wrist tip 7 are not rotated until they contact the mechanical stoppers. The meshing condition of the pairs of gears 63, 65; 73, 75 does not change. Namely, the bevel gears are not pressed against each other, nor they are disengaged from each other. Accordingly, if the gear box 10 and motors 61, 71 are turned back to the original positions, the positions of the driven members, i.e. the wrist body 6 and wrist tip 7 can be restored.

In order to remove motors 61, 71 from the gear box 10, the gear box 10 is turned. The motors 61, 71 are then ready to be taken out easily from the opening 102 with the bevel gear 63 on the output shaft 62 and the bevel gear 73 on the output shaft 72 attached to the motors 61, 71. This means that it is unnecessary to draw back the first and second transmission shafts 64, 74 in the axial directions thereof for disengaging the bevel gears thereon from those on the output shafts. Accordingly, it is also unnecessary to remove the belts 67, 77 from the pulleys 66, 76. Thus, the motors or detectors (position detectors or speed detectors) provided in the rear end portions of the motors are allowed to project to the outer side of the wrist base 5, and the motors can be removed. This enables the maintenance, inspection and replacement of the parts to be carried out easily.

According to the present invention, the motors in the wrist are arranged in the lengthwise direction thereof, so that the wrist can be miniaturized. Since the paths of transmitting the power from the motors are at right angles, the lengths of the power transmission paths increase due to the first and second transmission shafts 64, 74 which are part of these paths. However, the increase in the rigidity of the wrist, which is caused by the increase in the lengths of these transmission paths, can be minimized by providing the harmonic final reduction gears 601, 704 at the terminal ends of the transmission paths. Since the two motors are arranged in an opposed state, only one gear box for housing them need be provided. Moreover, since this gear box is formed so that it can be turned around the aligned axes of the first and second transmission shafts, the two motors are allowed to project or can be removed from the wrist base during the maintenance work without disassembling the gear box. This enables the maintenance work to be carried out easily.

Next, another embodiment, wherein a power transmitting method is different in part from a method of transmitting power to the wrist body 6 swingably mounted on the wrist base 5 and to the wrist tip portion 7 rotatably mounted on the wrist body 6 as explained in FIG. 1, will be described referring to FIG. 5. The present embodiment is the same in operation and effects of the invention as ones of the previously mentioned embodiment.

In the embodiment illustrated in FIGS. 1 to 4, the belt 67 and pulley 68 are used as a power transmitting means from the first transmitting shaft 64 to the swing shaft 69. In this embodiment, the first transmission shaft 64 is connected to the swing shaft 69 through a fourth transmission shaft 613 and bevel gears 611, 612, 614 and 615. Namely, the first transmission shaft 64 has the bevel gear 612 at a tip thereof and is connected to the fourth transmission shaft, which is perpendicular to the first transmission shaft 64, through the bevel gear 612 mounted on one end of the fourth transmission shaft 613. The fourth transmission shaft 613 has the bevel gear 614 at the other end thereof and is connected to the swing shaft 69 through the bevel gear 614 which is meshed with the bevel gear 615 mounted on the swing shaft 69.

Further, power transmission between the second transmission shaft 74 and the third transmission shaft 79 also is effected in a similar manner. Namely, the second transmission shaft 74 has a bevel

gear 711 at its tip, and the bevel gear 711 is meshed with a bevel gear 712 mounted on one end of a fifth transmission shaft 713 disposed perpendicularly to the second transmitting shaft 713. The fifth transmission shaft 713 has, at the other end thereof, another bevel gear 714 which is meshed with a bevel gear 715 of the third transmission shaft 79 perpendicular to the fifth transmission shaft 713, thereby connecting the third and fifth transmission shafts 79 and 713.

Next, a method of connecting electric wires both to the motor 71 and the motor 61 within the wrist base 5 is described referring to FIG. 6.The electric wires 801 are surrounded by flexible pipes 802, respectively. One end of each electric wire 801 is fixed to the wrist base 5 and connected to the motors 71, 61. The other end of each wire 801 is fixed to the forearm 4.The electric wires 801 pass through a hole which is formed in a gear 43 so as to be concentric with the wrist base 5.The electric wires 801 are provided along a central axis of the wrist base 5, so that the wires are twisted as the wrist base rotates. Deformation caused in the electric wire 801 is mainly one caused by twisting. The wires are easily deformed, so that they are not easily damaged.

3. Calculations