Haydon Kerk motion systems linear motion presentation 2010

Linear Systems
An 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 nuts
For 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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Leadscrew
The 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. Sold & Serviced By:

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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. Sold & Serviced By:

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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 Sold & Serviced By:

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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 grease
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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 Sold & Serviced By:

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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 Sold & Serviced By:

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. Sold & Serviced By:

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4th Generation Can-Stack Actuator

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Hybrid Style Linear Actuator

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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
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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. Sold & Serviced By:

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

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Putting It All Together
By 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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What is a Stepper Motor?

• 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.

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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
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0.100” lead screw the resolution will be: ELECTROMATE
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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 Sequence
The 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 Sequence
A 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
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36000 36mm 160 3 – 100 0.23 0.69
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Linear Velocity (inches per second):

• 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.
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percent load vs number of cycles

120
100
percent %

80
percent load vs
60
number of cycles
40
20
0
1 100 10000 1000000 1E+08

number of cycles

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Example: Life expectancy
• Let us assume that we have the following
application needs: 120
1. force = 15 lbs 100

percent %
2. travel = 3 inches 80
percent load vs
3. time to achieve the travel = 6 seconds 60
number of cycles
40
4. number of desired cycles = 1,000,000 20
5. linear velocity = 3 inches / 6 sec. = 0.5 0
inches per second 1 100 10,000 1,000,000 100,000,000
• Calculate the initial force based on number of
cycles desired
number of cycles
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 Hybrid
required = 15 lbs / .5 = = 30 lbs.
3. Convert this to Newtons. 30 / 0.225 = 133 Max. Power; Watts
Newtons Series Size L/R Chopper
• Convert travel to Meters:
1. 3 inches X 0.0254 = 0.0762 Meters 21000 8 0.3 0.37
• Calculate linear mechanical power: 28000 11 0.27 0.51
1. P lin = ( 133 Newtons x 0.0762 Meters ) / 6
sec = 1.7 watts 35000 14 0 .59 1.5
2. Using the frame size selection chart; the 43000 17 1.02 2.31
proper frame size would be the size 17
actuator: 57000 23 1.47 6
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• Choose resolution from curves. 87000 34 DNA 21.19 ELECTROMATE
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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.

Non-Captive External
Captive
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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

Power DC Supply
Supply Or Battery

DC Power User Interface
PC
Motion Profile:
(Speed, direction, Programmer
Power Pulses distance)
Mechanical Output Optional
Motor Driver Controller
PLC Microprocessor
Pre programmed

May be discrete May be discrete
Motor mounted or integral to
or part of larger drive
circuit
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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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IDEA Drive benefits
• 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 ELECTROMATE
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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 • Can be made with
screw lengths due to integral motor or powered
intermediate screw by your motor
supports • Mounting holes can be
• Very compact profile in the customized
standard configuration • Maintenance free
• Available in a wide
configuration that adds
additional stiffness and
grooves for mounting
sensors
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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 Customized Lead Screw Assemblies Dual Motion Stepper Motor Actuators

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Canstack Stepper Motor Actuators Motorized Linear Guides and Rails Patented Anti-Backlash Nuts
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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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Haydon Kerk motion systems linear motion presentation 2010

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Haydon Kerk motion systems linear motion presentation 2010