Haydon Kerk motion systems linear motion presentation 2010

Linear SystemsAn easy and economical way to put your ideas in motion

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Q: What is the most straightforward and effective way to design a machine or mechanism that requires precise linear positioning?



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Leadscrews and nutsFor over 30 years Haydon Kerk has been manufacturing linear systems using leadscrew and nut systems based on a polymer nut and a stainless steel leadscrew



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What are the key characteristics of the leadscrew?

Diameter, also referred to as the OD or major diameter. The diameter is typically chosen to meet the load requirements in the system.

Lead, this is the distance that nut would advance if you rotated the screw 360 degrees, this is commonly confused with the pitch.



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Lead – The axial distance a screw thread advances in a single revolution

Pitch – The axial distance measured between adjacent thread forms



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LeadscrewThe leadscrew provides a linear force using the simple mechanical principle of

the inclined plane. Imagine a steel shaft with a ramp (inclined plane) wrapped around it. The mechanical advantage (force amplification) is determined by the angle of the ramp which is a function of the lead, pitch, and diameter of the screw.



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• All of the screws are rolled (a cold forming process) from 303 stainless steel bars.

• Other materials have been rolled such as cold rolled steel, aluminum and titanium.



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• The rolling process offers a lot of benefits over ground or machined threads, these benefits include:– Increase lead accuracy, especially on longer

lengths– Highly polished screw surface for low friction

and long life– Economical to produce



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• When a leadscrew and nut are used to generate linear motion there are some clearances between the two parts to allow them to fit together without interference. These clearances are essential to the system but can lead to backlash or “lost motion” when reversing the direction of load.



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• When positional accuracy is not critical a freewheeling nut is a good solution.

• Haydon Kerk offers freewheeling (BFW) style nuts for all of our leadscrews



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What can be done to eliminate this ‘lost motion’?– If the system is mounted vertically gravity will

bias the nut to one side• Caution: High acceleration or certain speeds can

cause vibration, noise or momentary loss of positioning

– A biasing load such as a spring can be added to the system



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• A standard method for taking up backlash is to bias two nut halves axially using a precision shim or some form of compliant spring.

These mechanisms all increase drag torque in the system, but many styles of nuts have been developed for all kinds of

applications.ELECTROMATE

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• Two nut halves can be biased apart by a solid spacer but in order to keep the backlash to a minimum the system would need to be continuously adjusted.

• Instead of a solid shim an elastomeric ring is used to provide some compliance in the NTG series nut.

• This series allows the drag torque and stiffness to be specified and or set by the end user.

• The elastomeric ring provides a small amount of wear compensation.



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• This simple compression type spring between two nut halves is a simple solution but does have some drawbacks:– The nut is very stiff in only one direction, the opposite direction is

only as stiff as the spring– To move a 10 pound load you would need to have at least a 10

pound preload on the spring system this leads to high drag torques and high wear rates

• For lightly loaded applications or vertical applications where some dampening is required Haydon Kerk offers the CMP (Compression) Style anti backlash nut.



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• For increased stiffness with a reduction in drag torque the Wedge series (WDG) nut is a good choice.

• Through the use of a collapsible wedge the spring force is multiplied by about 5 to 1 to increase the stiffness.

• The nut can be ‘back driven’ meaning it will not bind up on unevenly worn screws.



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• Another method of biasing the two nut halves is to use another threaded member in conjunction with a torsion spring to ‘push’ on one nut half.

• Haydon Kerk’s KHD and VHD series nut’s use this technology.

• These designs are optimized for higher load type applications where axial stiffness and low drag torque are required.



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• In instances where there is a light load, vibration or noise present the ZBX series of nuts is a good economical solution.

• The nut uses a collet style mechanism to collapse radially onto the screw threads and remove both axial and radial clearances in the nut.



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• The ZBX nut is for lightly loaded applications, in cases where a higher load is required the ZBA style replaces the spring mechanism with a threaded solid collar that biases the collet fingers radially inward.

• This threaded collar allows adjustment of the preload on the nut (drag torque).



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• The most flexible design is the NTB nut which offers excellent axial stiffness, low drag torque and is easily customized.

• The NTB nut is available across the entire range of leadscrew sizes.

• Caution needs to be exercised when using this nut with very fine leads, Kerkote TFE coating is recommended.



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• For small or compact applications a ‘mini’ series of nuts is available in the BFW, NTG and NTB series.

• Coming this summer is a ‘micro’ series based on a line of 2mm diameter leadscrews.



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Custom Nut Materials• Haydon Kerk’s most common nut material is a

poly acetal that is fortified with Teflon for lubricity.

• Haydon Kerk offers more than a dozen custom materials (Poly acetal, Nylon, PPS etc.) both with and without carbon fiber reinforcement.

• The carbon fiber reinforcement is critical in applications that require a wide operating temperature range or a high load capacity.



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Leadscrew Coatings• While many of the different nuts series

work well without any additional lubrication there are several reasons to use a lubricant (either a solid film type lubricant or a grease) these reasons are:– Increased life– Reduced drag– Improved efficiency– Dampens noise and vibration



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• Haydon Kerk offers two different types of TFE coating for our leadscrews:– Kerkote is a soft type of TFE coating that works well

to reduce friction and noise– Black Ice is a harder type of TFE coating that is

suitable for harsh environments• In applications where grease is allowable

Haydon Kerk offers several types of lubricants.– Not all nut series are compatible with grease, the

CMP and BFW series are fully compatible with greaseELECTROMATE


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Leadscrew and Nut Part Numbering



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• Don’t let the standard catalog nuts or leadscrews limit your designs

• Haydon Kerk has the capability to:– Design custom dies to

make new diameters or leads

– Design and make custom molds

– Blend custom materials to get the optimum properties for your application

– Machine the screw to your finished requirements



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Motor Technology• Haydon Kerk has

specialized in stepper motor based linear actuators for over 30 years.

• There are two distinct motor technologies used, canstack stepper motors and hybrid stepper motors. ELECTROMATE


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• The general design of the canstack motors is all very similar.

• Haydon Kerk offers motors from 15mm to 46mm in diameter.

• The rotary to linear conversion is accomplished right inside the motor for the most compact assembly size.



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4th Generation Can-Stack Actuator



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Hybrid Style Linear Actuator



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Motor Styles

Both Hybrid and Can-Stack motors are available in three linear configurations.



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• A Non Captive style actuator simply has a threaded nut inside the rotor and the leadscrew passes through the motor.

• The screw must be secured in the application to keep it from rotating to get linear motion.

• The internal threads have some clearances to allow for misalignment in the system.



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• A Captive style actuator makes use of the same internal threaded components but includes a spline shaped shaft that is captured by a front sleeve to prevent rotation.



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• The third configuration uses a nut that is external to the motor, the screw is fixed to the rotor. This configuration is referred to as an External Linear style actuator. The nut must be held captive to get linear motion.



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Integrated NutOf equal, if not greater importance to the lead screw is the nut that

drives the screw. The nut is imbedded in the rotor of the stepping motor (captive and non captive styles), which makes this actuator configuration unique from other rotary to linear techniques.



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By injection molding plastic threads within a brass rotor assembly, both characteristics of low friction and high bearing journal stability is achieved

Hybrid rotor construction



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Putting It All TogetherBy combining all components as explained above, the

stepper motor-based linear actuator is created. The following figure is a cross sectional view of a “captive” type linear actuator. “Captive” indicates that there is already an anti-rotation mechanism built into the actuator through the use of a spline “anti-rotation” shaft and a “captive sleeve”.



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Cross sectional view of a hybrid captive linear stepping actuator



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• A stepper motor is a brushless electric motor that can divide a full rotation into a number of smaller ‘steps’.

• These smaller steps are commonly referred to as the step angle of the motor.

What is a Stepper Motor?



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• Can-stack motors can have a step angle of 3.75, 7.5 or 15 rotational degrees for each input pulse.



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• Hybrid motors can have a step angle of 0.9 or 1.8 rotational degrees for each input pulse.



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Resolution, Accuracy, & Repeatability…

What’s the difference??



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RESOLUTION:

The incremental distance the actuator’s output shaft will extend per input pulse (mm/step or in/step)

Formula: LEAD (360 degrees / step angle)

Example:For a 1.8 degree hybrid there are 200 steps per revolution, if you have a

0.100” lead screw the resolution will be:0.100”/200 steps = 0.0005”/step



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ACCURACY:

The difference between the theoretical distance and the actual distance traveled is the actuator’s accuracy.

Example: For a hybrid actuator utilizing a screw with a 1” lead, 360 deg of rotary motion will result in a theoretical 1” stroke. In general, the tolerance of a Haydon hybrid linear actuator with a 1” move will be +/- 0.0005”



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REPEATABILITY:

The range of positions attained when the actuator is commanded to approach the same target multiple times under identical conditions.



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• Haydon Kerk offers literally thousands of catalog combinations of linear stepper actuators based on:– Motor technology

• Can-stack• Hybrid

– Motor Configuration• Captive• Non captive• External linear• Rotary (Can-stacks only)

– Resolution– Winding Configuration



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Q: How does a stepper motor work?



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Stepper motors are 2 phase devices. Rotors are constructed of permanent magnet materials. The rotor interacts with the mild steel stator which is allowed to change its polarity based on the input signals to each coil of each phase.

Every input pulse or step causes the rotor to rotate a given degree of rotation.

Two commonly used schemes for driving the stepper motor are “ One-Phase ON stepping” and “Two Phase ON stepping”



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“One-Phase On” Stepping SequenceThe following figure illustrates a typical step sequence for a simplified 2 phase motor. In

step 1, phase A of the 2 phase stator is energized. This magnetically locks the rotor in the position shown, since unlike poles attract. When phase A is turned off and phase B is turned on, the rotor moves 90° clockwise. In step 3, phase B is turned off and phase A is turned on but with the polarity reversed from step 1. This causes another 90° rotation. In step 4, phase A is turned off and phase B is turned on, with polarity reversed from step 2. Repeating this sequence causes the rotor to move clockwise in 90° steps.



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“Two-Phase On” Stepping SequenceA more common method of stepping is “two phase on” where both phases of

the motor are always energized. However, only the polarity of one phase is switched at a time, as shown in the following figure. With two phase on stepping, the rotor aligns itself between the “average” north and “average” south magnetic poles. Since both phases are always on, this method provides 41.4% more torque than “one phase on” stepping.



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How to properly size a linear actuator



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Minimum Information Needed:

• The force needed to move a load. (expressed in Newtons)

• The distance that the load is to be moved. (expressed in meters)

• The time required to move the load the given distance (expressed in seconds)

• The mechanical power is then calculated in watts • The required life



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Linear power: P lin ( watts ) ::

P lin = (distance traveled in Meters) (force in Newtons) Time to travel the distance in Seconds = watts



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Hybrid

Max power; watts

Series Size Max Force (N) Linear Travel/Step (micron) L/R Chopper

21000 8 45 1.5 – 40 0.3 0.37

28000 11 90 3 – 50 0.27 0.51

35000 14 220 1.5 – 50 0.59 1.5

43000 17 220 1.5 – 50 1.02 2.31

57000 23 880 4 – 50 1.47 6

87000 34 2200 12.7 – 127 DNA 21.19

Can-stack

Max power; watts

Series Size Max Force (N) Linear Travel/Step (micron) L/R Chopper

15000 15mm 7 20 0.025 0.03

20000 20mm 16 25 – 100 0.05 0.06

Z20000 20mm 35 25 – 100 0.09 0.23

26000 26mm 50 6 – 100 0.17 0.18

Z26000 26mm 80 6 – 100 0.18 0.48

36000 36mm 160 3 – 100 0.23 0.69

46000 46mm 260 12.7 – 400 0.55 1.13ELECTROMATE


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• When we calculated the mechanical output power, we defined the force, speed and travel.

• We now need to calculate the linear velocity

• The linear velocity (inches per second) is:

V lin = travel (inches) Time to achieve the travel (seconds)

• The force vs. linear velocity curves are used to determine proper resolution of the leadscrew to be used.

Linear Velocity (inches per second):



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percent load vs number of cycles

020406080

100120

1 100 10000 1000000 1E+08

number of cycles

perc

ent % percent load vs

number of cycles



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Life expectancy

020406080

100120

1 100 10,000 1,000,000 100,000,000

number of cycles

perc

ent % percent load vs

number of cycles

Example:•

Let us assume that we have the following application needs:

1. force = 15 lbs2. travel = 3 inches3. time to achieve the travel = 6 seconds4. number of desired cycles = 1,000,0005. linear velocity = 3 inches / 6 sec. = 0.5

inches per second•

Calculate the initial force based on number of cycles desired

1. From the percent load vs. number of cycle table determine the % loss after the 1,000,000 cycles.

2. This = 50%; Therefore the initial force required = 15 lbs / .5 = = 30 lbs.

3. Convert this to Newtons. 30 / 0.225 = 133 Newtons

•

Convert travel to Meters:1. 3 inches X 0.0254 = 0.0762 Meters

•

Calculate linear mechanical power:1. P lin = ( 133 Newtons x 0.0762 Meters ) / 6

sec = 1.7 watts2. Using the frame size selection chart; the

proper frame size would be the size 17 actuator:

Hybrid

Max. Power; Watts

Series Size L/R Chopper

21000 8 0.3 0.37

28000 11 0.27 0.51

35000 14 0 .59 1.5

43000 17 1.02 2.31

57000 23 1.47 6

87000 34 DNA 21.19• Choose resolution from curves. ELECTROMATEToll Free Phone (877) SERVO98


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Example continued:

• Verify your selection by checking force at required step rate.

1. The resolution we chose is “J”. (0.00048 inches per step)

2. Linear velocity = 0.5 inches per second

3. Step rate = 0.5 / 0.00048 = 1041 steps per second

4. Verify that the required force is present at 1041 steps per second using the force vs step rate curve.



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Maximum Load:

• The maximum load rating for each frame size actuator is shown on the force vs. step rate curve and appears as a horizontal dotted line labeled, “Recommended Load Limit”.

• Operating the actuator in excess of this value can result in bearing and /or thread damage and therefore premature life.



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Can-stack actuators are offered in a complete family of sizes that range from 15mm – 46mm with output forces of 7 N to 260 N.

Captive Non-Captive External



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Can-Stack Part Numbering



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Hybrid actuators are also offered in a complete family of sizes that range from 21mm – 87mm (NEMA Size 8 – Size 34) with output forces of 45 N to 2200 N.

Captive Non-Captive External



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Hybrid Part Numbering



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How do you make a stepper motor move?



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Linear Actuator Drives:

• Stepper motor based linear actuators are two-phase devices that are required to be run by the appropriate drive electronics.

• These drives are either L/R drives (constant voltage) or chopper drives (constant current).

• Chopper drives are the predominant drives being used in the industry.

• L/R drives are used, but usually when a low voltage supply is available. (6 volt battery as an example).



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Drives – Typical Stepper Motor Control System

DriverMotor Controller

Power Supply

User Interface

OptionalMechanical OutputPower Pulses

DC Power

DC SupplyOr Battery

PCProgrammer

PLC MicroprocessorPre programmed

May be discrete Motor mounted or part of larger circuit

May be discrete or integral to drive

Motion Profile: (Speed, direction, distance)



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IDEA Drive• A new chopper drive

that can be mounted directly on a size 17 actuator or is available as a stand alone drive



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• Single compact package – controller and driver all in one

• Available mounted to a size 17 actuator or as a stand alone unit

• Simple programming through a GUI (Graphical User Interface)

• Automatic population of motor and drive parameters• USB communication• 8 opto-isolated input/output ports• +12 to +48VDC input range• Simple programming and command set allows a user to

begin using the drive quickly• Micro-stepping capability from full step to 1/64 step

IDEA Drive benefits



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Guided Linear Assemblies• Guided linear rail

assemblies are available with or without a stepping motor

• Rails are available in a wide range of sizes and configurations



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Rapid Guide Screw RGS• The RGS is available

with– 4 different diameter

screws– 6 different frame sizes– Over 20 different leads– Each frame size is

available with two different motor frame sizes



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Benefits of the RGS• Can accommodate long

screw lengths due to intermediate screw supports

• Very compact profile in the standard configuration

• Available in a wide configuration that adds additional stiffness and grooves for mounting sensors

• Can be made with integral motor or powered by your motor

• Mounting holes can be customized

• Maintenance free



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RGS Part Numbering



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Linear Rail System LRS• The LRS was designed around

standard T-slot profiles to allow the use of commercially available hardware

• Designed for the size 17 actuator series

• Easily accepts any anti backlash nut available for the ¼” diameter screw

• Has a wear compensating sliding bearing system, never needs user adjustment

• Can be used as a structural member in your system



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LRS Part Numbering



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Screw Rail Actuator SRA• When space is at a

premium the SRA is a lead screw and support rod all in one

• Is also available in an anti backlash version

• Is available in 4 different frame sizes



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SRA Part Numbering



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Guide Rods and Spline Rods• Guide Rods and

Spline Rods with linear bushings are available also

• Spline Rods are available with an anti- backlash version



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Guide and Spline Rod Part Numbering



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Hybrid Stepper Motor Actuators

Canstack Stepper Motor Actuators

Customized Lead Screw Assemblies Dual Motion Stepper Motor Actuators

Motorized Linear Guides and Rails Patented Anti-Backlash NutsELECTROMATE


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Haydon Kerk Motion Solutions capabilities include:

• Custom designs, specifically honed to the customer’s needs.



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Please visit us at

www.HaydonKerk.com



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http://www.haydonkerk.com/