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421:. Highest accuracy signals are obtained if the Lissajous figure is circular (no gain or phase error) and perfectly centred. Modern encoder systems employ circuitry to trim these error mechanisms automatically. The overall accuracy of the linear encoder is a combination of the scale accuracy and errors introduced by the readhead. Scale contributions to the error budget include linearity and slope (scaling factor error). Readhead error mechanisms are usually described as
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556:. Enclosed linear encoders are employed in dirty, hostile environments such as machine-tools. They typically comprise an aluminium extrusion enclosing a glass or metal scale. Flexible lip seals allow an internal, guided readhead to read the scale. Accuracy is limited due to the friction and hysteresis imposed by this mechanical arrangement.
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US Patent 3820110, "Eddy current type digital encoder and position reference", gives an example of this type of encoder, which uses a scale coded with high and low permeability, non-magnetic materials, which is detected and decoded by monitoring changes in inductance of an AC circuit that includes an
225:
principles. Optical encoders are the most accurate of the standard styles of encoders, and the most commonly used in industrial automation applications. When specifying an optical encoder, it's important that the encoder have extra protection built in to prevent contamination from dust, vibration and
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Distance coded reference marks (DCRM) are placed onto the scale in a unique pattern allowing a minimal movement (typically moving past two reference marks) to define the readhead's position. Multiple, equally spaced reference marks may also be placed onto the scale such that following installation,
462:
In either case, the encoder will output quadrature squarewaves, with the distance between edges of the two channels being the resolution of the encoder. The reference mark or index pulse is also output in digital form, as a pulse which is one to four units-of-resolution wide. The output signals may
491:
Most incremental, linear encoders can produce an index or reference mark pulse providing a datum position along the scale for use at power-up or following a loss of power. This index signal must be able to identify position within one, unique period of the scale. The reference mark may comprise a
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has two digital output signals, A and B, which issue quadrature squarewaves. Depending on its internal mechanism, an encoder may derive A and B directly from sensors which are fundamentally digital in nature, or it may interpolate its internal, analogue sine/cosine signals. In the latter case, the
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as they repeat every scale period. The largest contributor to readhead inaccuracy is signal offset, followed by signal imbalance (ellipticity) and phase error (the quadrature signals not being exactly 90° apart). Overall signal size does not affect encoder accuracy, however, signal-to-noise and
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so as to improve noise immunity. An early industry standard was 12 μA peak-peak current signals but more recently this has been replaced with 1V peak to peak voltage signals. Compared to digital transmission, the analog signals' lower bandwidth helps to minimise
434:. Phase is more difficult to compensate dynamically and is usually applied as one time compensation during installation or calibration. Other forms of inaccuracy include signal distortion (frequently harmonic distortion of the sine/cosine signals).
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The major advantages of linear incremental encoders are improved noise immunity, high measurement accuracy, and low-latency reporting of position changes. However, the high frequency, fast signal edges may produce more EMC emissions.
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In an incremental system, position is determined by motion over time; in contrast, in an absolute system, motion is determined by position over time. Linear encoder technologies include optical, magnetic, inductive, capacitive and
516:, digital code, or pseudo-random code) an encoder can determine its position without movement or needing to find a reference position. Such absolute encoders also communicate using serial communication protocols. Many of these
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Capacitive linear encoders work by sensing the capacitance between a reader and scale. Typical applications are digital calipers. One of the disadvantages is the sensitivity to uneven dirt, which can locally change the
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The sensors are based on an image correlation method. The sensor takes subsequent pictures from the surface being measured and compares the images for displacement. Resolutions down to a nanometer are possible.
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Inductive technology is robust to contaminants, allowing calipers and other measurement tools that are coolant-proof. A well-known application of the inductive measuring principle is the
Inductosyn.
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readheads. With coarser scale periods than optical encoders (typically a few hundred micrometers to several millimeters) resolutions in the order of a micrometer are the norm.
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are frequently included such that on power-up the controller can determine if the encoder is at an end-of-travel and in which direction to drive the axis.
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other conditions common to industrial environments. Typical incremental scale periods vary from hundreds of micrometers down to sub-micrometer.
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the desired marker can either be selected - usually via a magnet or optically or unwanted ones deselected using labels or by being painted over.
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Magnetic linear encoders employ either active (magnetized) or passive (variable reluctance) scales and position may be sensed using sense-coils,
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Servo controlled motion systems employ linear encoder so as to provide accurate, high-speed movement. Typical applications include
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578:) and plastics. The scale may be self-supporting, thermally mastered to the substrate (via adhesive or adhesive tape) or
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For the highest accuracy, lowest measurement hysteresis and lowest friction applications, open linear encoders are used.
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Quadrature sine/cosine signals can be monitored easily by using an oscilloscope in XY mode to display a circular
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Linear encoders are transducers that exploit many different physical properties in order to encode position:
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jitter performance may degrade with smaller signals. Automatic signal compensation mechanisms can include
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automatic offset compensation (AOC), automatic balance compensation (ABC) and automatic gain control (AGC)
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interpolation process effectively sub-divides the scale period and thereby achieves higher measurement
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that encodes position. The sensor reads the scale in order to convert the encoded position into an
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826:. Digital Scale and DRO Systems. Mitutoyo. September 2009. Bulletin No. 1976. Archived from
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inductive coil sensor. Maxon makes an example (rotary encoder) product (the MILE encoder).
156:, which can then be decoded into position by a digital readout (DRO) or motion controller.
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570:. Scale materials include chrome on glass, metal (stainless steel, gold plated steel,
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Many linear encoders include built-in limit switches; either optical or magnetic. Two
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Optical linear encoders dominate the high resolution market and may employ shuttering/
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As well as analog or digital incremental output signals, linear encoders can provide
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852:"Gear Manufacture - Industries - Wenzel UK - Co-ordinate Measuring Machines - CMM"
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Visualization of magnetic structures of a linear encoder (recorded with MagView).
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Linear encoders may use transmissive (glass) or reflective scales, employing
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The industry standard analog output for linear encoders is sine and cosine
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are now appearing, which avoid tying users to a particular supplier.
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are proprietary (e.g., Fanuc, Mitsubishi, FeeDat (Fagor
Automation),
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and high precision machining tools ranging from digital calipers and
176:. Linear encoders are used in metrology instruments, motion systems,
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single feature on the scale, an autocorrelator pattern (typically a
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PCB assembly equipment; semiconductors handling and test equipment,
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mounted. Track mounting may allow the scale to maintain its own
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EnDat, DriveCliq, Panasonic, Yaskawa) but open standards such as
933:
Position
Sensing: Angle and Distance Measurement for Engineers
901:
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There are two main areas of application for linear encoders:
877:"Océ Production Digital Presses - Color High Speed Printers"
586:
and allows large equipment to be broken down for shipment.
172:. Optical technologies include shadow, self imaging and
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mills, manufacturing gantry tables and semiconductor
695:"ABS Coolant Proof Caliper Coolant Proof Micrometer"
385:
Linear encoders can have analog or digital outputs.
46:. Unsourced material may be challenged and removed.
230:can provide resolutions as fine as a nanometer.
921:Linear Position Sensors: Theory and Application
8:
237:Optical linear encoder mounted on Mitutoyo
512:With suitably encoded scales (multitrack,
248:, visible LEDs, miniature light-bulbs and
340:, gear measurement, tension testers, and
106:Learn how and when to remove this message
798:. FRABA, Inc. 2012-04-23. Archived from
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119:
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405:signals. These are usually transmitted
780:: CS1 maint: archived copy as title (
773:
639:Distance coded reference marks (DCRM)
463:be directly transmitted to a digital
124:Three typical linear optical encoders
7:
821:"MICSYS - 2D Nano-Resolution Sensor"
728:. Ruhle Companies, Inc. 2015-03-09.
244:Light sources used include infrared
44:adding citations to reliable sources
544:Physical arrangement and protection
483:reference or positioning signals.
14:
584:coefficient of thermal expansion
328:Measurement application include
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732:from the original on 2020-05-27
446:The A and B quadrature channels
31:needs additional citations for
548:Linear encoders may be either
1:
954:Electromechanical engineering
465:incremental encoder interface
330:coordinate-measuring machines
182:coordinate measuring machines
854:. Wenzel CMM. Archived from
397:The sine and cosine outputs.
633:Index/reference mark/datum/
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925:John Wiley & Sons Inc.
670:"Linear magnetic encoders"
475:Absolute reference signals
427:sub-divisional error (SDE)
159:The encoder can be either
144:or readhead paired with a
919:Nyce, David S. (2003).
467:for position tracking.
931:Hans, Walcher (1994).
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937:Butterworth-Heinemann
672:. RLS. Archived from
611:Signal-to-noise ratio
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376:Output signal formats
279:relative permittivity
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204:Scale/reference based
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307:Optical image sensor
40:improve this article
923:. New Jersey, USA:
452:incremental encoder
381:Incremental signals
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196:Physical principle
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342:digital read outs
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902:"BiSS Interface"
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879:. Archived from
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624:Lissajous figure
419:Lissajous figure
266:magnetoresistive
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55:"Linear encoder"
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650:Rotary encoder
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532:Limit switches
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407:differentially
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362:pick-and-place
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348:Motion systems
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334:laser scanners
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302:Without scales
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138:linear encoder
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883:on 2009-10-10
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858:on 2009-03-28
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833:on 2011-10-13
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763:on 2010-08-13
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601:Repeatability
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508:Absolute code
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51:Find sources:
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29:This article
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885:. Retrieved
881:the original
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860:. Retrieved
856:the original
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835:. Retrieved
828:the original
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804:. Retrieved
800:the original
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758:the original
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734:. Retrieved
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702:the original
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423:cyclic error
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366:wire bonders
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316:Applications
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293:Eddy current
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250:laser diodes
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170:eddy current
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38:Please help
33:verification
30:
726:"Bar Scale"
494:Barker code
414:emissions.
324:Measurement
262:Hall effect
223:holographic
219:diffraction
184:to stages,
161:incremental
948:Categories
887:2009-10-29
862:2009-10-28
837:2011-11-15
806:2011-11-02
767:2009-11-05
736:2020-05-27
711:2011-11-15
680:2009-10-30
656:References
629:Quadrature
606:Hysteresis
596:Resolution
522:Heidenhain
457:resolution
403:quadrature
272:Capacitive
142:transducer
96:April 2022
66:newspapers
518:protocols
500:pattern.
450:A linear
285:Inductive
165:absolute.
776:cite web
730:Archived
644:See also
635:fiducial
550:enclosed
481:absolute
354:robotics
344:(DROs).
338:calipers
256:Magnetic
190:steppers
576:Zerodur
514:vernier
496:) or a
438:Digital
332:(CMM),
209:Optical
80:scholar
619:jitter
564:Ronchi
389:Analog
150:analog
82:
75:
68:
61:
53:
831:(PDF)
824:(PDF)
761:(PDF)
754:(PDF)
705:(PDF)
698:(PDF)
615:noise
580:track
572:Invar
498:chirp
215:moiré
146:scale
87:JSTOR
73:books
782:link
554:open
526:BiSS
246:LEDs
59:news
566:or
552:or
425:or
412:EMC
264:or
239:CMM
221:or
186:CNC
163:or
152:or
42:by
950::
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