Rack and Pinion Shaft Encoder
or Resolver Measuring Systems
If you are searching for any of the following
products:
- Precision Rack and Pinion Shaft Encoder or Resolver
Measuring Systems for NCs, CNCs, PLCs, DROs and retrofitters/rebuilders of Machine Tools
- Accurate Motion Control Feedbacks for lathes, milling
machines and other Machine Tools
- Reliable Linear and Angular Positioning
- Instrument Gears, Racks and
Gearboxes for robotics, aerospace, automotive, control automation and medical
industries
Look no further. You'll find it
at Schlenker Enterprises' Actuation for Motion Control!
The fundamental operation
of Reliance/SEL Series Precision Rack and Pinion Linear Encoder or Resolver Measuring
Systems
Precision measuring in the environment of machine tools is
a tough job. The most important component in providing the ultimate in both reliability
and precision is a rack and pinion linear encoding device.
A Rack and Pinion Linear Encoder or Resolver System
incorporates lengths of precision measuring racks; and enclosed channel; and an
incremental rotary encoder or resolver with an integral pinion. Our racks are ground with
a crown which reduces the need for precision pinion alignment. As motion occurs, the
pinion rotates along the racks causing the encoder/resolver contained within the sealed
housing to rotate. This rotation reflects the change in linear positions, and the velocity
is determined by the frequency of pulses coming from the encoder/resolver.
The channel is a piece of steel, physically connected to
the machine. Constructed of machine steel, the channel has the same thermal coefficient of
expansion as machinery and will expand and contract at the same rate.
The precision racks are hardened and ground #416 Stainless
Steel. The racks are mounted with pitch line on the neutral axis of the channel and laser
calibrated to avoid cumulative errors. The rack, mounted to the channel, is surrounded by
seals over the entire length of travel to prevent contamination. As an additional
precaution against particles adversely affecting performance, the rack’s teeth are
facing down. If any contaminants to penetrate the lipped seals, they will fall harmlessly
to the bottom of the housing or are wiped away by the wiping action of the pinion and rack
teeth.
The pinion is hobbed to AGMA Q15 integral in the
shaft of the rotary encoder/resolver. The pinion is lightly spring loaded against the rack
to keep the total backlash under .0001 inches. The pinion is constructed of a metal softer
than the ground rack to allow the pinion to be honed to the rack pattern. Once matched to
the rack pattern, there will be negligible wear on the pinion due to the light preload and
minimal encoder inertia.
 Years of
Trouble Free Operation
A rack and pinion style incremental linear encoder or
resolver combined with a ruggedly constructed DRO, NC, CNC or PLC provides the user with
years of trouble-free operation.
Tolerates
Coolant and Metal Chips
A rack and pinion style encoder or resolver is the most
reliable feedback device for operation in an environment where coolant and metal chips are
ever present. One advantage of the SEL Series linear encoder or resolver package is that
coolant does not affect either the rack or the pinion. By comparison, a glass scale will
either fail or require ongoing cleaning and maintenance after coolant seeps through the
encoder seals.
The SEL Series features a unique dual lip seal to inhibit
the flow of metal chips into the rack and pinion area. When a metal chip penetrates the
single seal on a glass or magnetic scale, it will often render the feedback device
inoperable causing a need for system repair and most likely replacement. If a metal chip
does enter the SEL Series enclosure, a flexplate simply flexes and allows the pinion to
ride over the metal chip without damage to the encoder or error in the readout at final
position.
Long Life in
Hostile Environment
It is well accepted that the rack and pinion linear systems
have a high degree of dependability and life while operating in the rugged environment of
the machine tool. We have not had a rack wear out in over 20 years of providing crowned,
ground racks for precision position feedback.
Maintenance
Free Operation
The SEL Series Rack and Pinion Systems are rarely affected
by the environment and tolerate metal chips and coolant. Under normal operating
conditions, the rack and pinion system will not require maintenance over the life of the
unit.
Operates in
Shock and Vibration Conditions
The Linear Encoder or Resolver Package is designed to
operate in shock conditions. Specifications far exceed those of glass or magnetic scales.
If fact, a glass scale will likely break under conditions approaching the upper limits of
a rack and pinion specification.
Precise
Operation
Accuracy on a machine tool is dependent on the readout
system’s ability to measure the actual position of the tool relative to the work
piece. It is critical that the feedback device adapt to temperature changes without
creating errors.
There are two main reasons why a rack and pinion feedback
measuring system creates fewer temperature related errors:
- The thermal coefficient of expansion is identical to that of
machinery steel.
- The rack is attached directly to the machine via the
channel. The rack will only change with the machine, not the air around the machine.
- Being suspended in air, glass and magnetic scales are
affected by air temperature not machine temperature.
Fine
Resolution
A resolution of 50 millionths of an inch (.000050")
provides fine resolution for grinding applications and .0001 inch diameter increments for
lathes, milling machines or any other machines.
Unlimited
Length of Travel
Due to the unique construction of the SEL Series Rack and
Pinion Encoder or Resolver Measuring System Package, there is really no limitation to the
length of travel. The SEL Series is accurate to +/- .0005 inches regardless of length.
There is no cumulated error.
Integral
Pinion Transducers
Both resolvers and encoders are totally sealed with MS
connectors; and are available with either 1 mm or 1/20 inch circular pitch, 20 tooth
integral (quality 15) pinions for 0.002 mm or 0.001 inch resolution as commonly required.
10 tooth, 1/10 inch circular pitch pinion shaft encoders for interfacing with 0.100 inch
pitch rack are available also. Other resolutions are available to 0.00002 inches (or
0.0004mm)
Backlash
Elimination
Our unique Flexplates eliminate all system backlash
and pivot around the rack pitch line permitting as much as 0.015 inch variation between
the fixed and moving members without affecting the measuring accuracy. Repeatability in
within 0.000025” over the total length of travel.
Neutral Axis
Concept
The Rack Channel has been designed such that neutral
axes in bending intersect at the pitch line of the rack. This theory has been proven in
practice. The calibrated accuracy of the rack assembly is not altered when it is mounted
on a machine. This can result in significant savings for machinery builders because
mounting surfaces need not be perfectly flat (+/-0.0001” change in accuracy).
System
Accuracy
This is an non-contact system at the point of converting a
mechanical motion into an electronic position signal. In any non-contacting measuring
system a precision air gap must be maintained between the moving member and the sensors.
Our air gap is within the rotating transducer and accurately maintained by high quality
bearings. It is easier to maintain closer tolerances with instrument size components with
small ABEC 7 ball bearings than a large machine member with large bearings.
Total measuring accuracies within 0.001 inch over most any
length of travel are commonplace with either open rack or protected rack channel; and
accuracies within 0.0005” are possible by use of laser calibration of special Grade 4
rack on a machine combined with Quality 15 pinion shaft encoders or resolvers.
Repeatability
With Protected Rack Channel, 0.0001”
bi-directional repeatability can be expected.
Angular
Measuring Rack Systems
Our AMR (Angular Measuring Rack) system is supplied as a
rack set, to suit a specified diameter. The range is from 570 mm upwards with close
intervals between possible working diameters. When included in an initial design concept,
the AMR gives particular benefits. The measuring radius is a large percentage, usually
from 50 to 80 percent of the maximum working radius producing high repeatability.
No axial space is needed below the table. This makes it
lower and stiffer along with other parts of the machine increasing machine working rates
and repeatability.
For more information or ordering assistance
you may contact us at:
Schlenker Enterprises, Ltd.
5143 Electric Avenue
Hillside, IL 60162
Phone: 708/449-5700
Fax: 708/449-5703
E-mail: jschlenk@aol.com
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