This guide answers most often-asked questions about encoders general H

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This guide answers most often-asked questions about encoders general H

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Encoder Questions Answers Application Brief M-101
This guide answers most often-asked questions about encoders general HewlettPackard encoders particular. organized into following sections: General Encoding Output Waveforms Resolution Mounting Materials Reliability Electrical Miscellaneous
General Encoding
Question What encoder? Answer. encoder sensor mechanical motion. translates motion (such position, velocity, acceleration) into electrical signals. Question What kinds encoders available? Answer. three basic types encoders contact (also called resistive potentiometers), magnetic, optical. Contact encoders either wiper which picks voltage corresponding position, brush
5965-5974E
series brushes which wipe along codewheel with alternating conductor/insulator pattern. pattern insulator conductor corresponds mechanical position. Magnetic encoders sense magnetic field which changes according mechanical position. Examples magnetic encoders include synchros, resolvers, Hall effect sensors. Optical encoders have light source which shines through reflects codewheel codestrip photodetector. photodetector sees pattern light dark which corresponds mechanical position. Encoders generate either analog digital output signals. analog encoder voltage series voltages corresponding position, velocity, etc. digital encoder puts signals which represent binary (logic level high low). coding determines position. Question What difference between absolute incremental encoder? Answer. Absolute encoders have unique value (voltage, binary
count) each mechanical position thus position known "absolutely". power position absolute encoder known. Incremental encoders have output signals which repeat over range motion thus each mechanical position uniquely defined. current position sensed only incremental from last position sensed. Thus power position incremental encoder known since output signals unique singular position. Count direction information obtained from both absolute incremental encoders. Question What channel? Answer. channel electrical output signal from encoder. Typical high performance incremental encoders have either three channels. Question What quadrature? Answer. encoders have channels which output identical repeating square waves motion occurs. Channel offset from channel half
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high pulse square wave either channel. Quadrature offset relationship between channel channel Question What meant decoding? Answer. rising edge rising edge (called Cycle) either channel signifies that window pair codewheel rotated photodetector array. Because quadrature, four unique logic states defined each window pair that mechanically passes. When these four unique logic states decoded, resolution obtained times (4X) resolution codewheel. Thus codewheel with window pairs decoded into 2000 quadrature states. Figure more details.
describe output waveforms? Answer. Other terms industry include: Answer. index pulse occurs Phase: rising edge rising edge (This equivalent third channel called channel HP's State width. defines pulse occurs this channel once each full revolution phase center high codewheel. Essentially, this pulse state center high state marks singular position codewheel. This absolute ref- Flutter: variation from cycle adjacent cycle. erence added incremental Duty Jitter, Waterfall: variation encoder. from pulse width adjacent pulse width. Question Cycle, Pulse Width, State Width, which Symmetry: ratio between pulse high pulse (nominally most consistent? unity). Answer. Cycle most consis- Edge Edge Variation, Edge tent. trying measure Separation, Phase Error: equivavelocity timing between edges, lent State Width Error. Phase Jitter: variation from rising rising rising falling edge rising edge falling) either channel Pulse width state width Question encoders consistent. provide analog outputs (sinusoidal quasi-sinusoidal Question What other terms used within industry signals)? Question What index pulse? Answer. encoders provide only digital incremental output waveforms.
Resolution
Question does define resolution? Answer. typically talk terms line density, which number window pairs unit length. Line density expressed either lines inch (LPin) lines (LPmm). rotary encoder, line density given
AMPLITUDE
ROTATION CYCLE WINDOW PAIR, 360°e) LOGIC STATE WIDTH STATES WINDOW PAIR, EACH STATE 90°e) PULSE WIDTH (RISING FALLING 180°e) INDEX CHANNEL (ONE PULSE FULL CODEWHEEL REVOLUTION)
LPin (LPmm)
Counts Revolution (Rop)
Figure Output Waveforms.
This gives number window pairs unit length given optical radius (Rop).
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linear encoder modules, resolution number window pairs unit linear length. Alternative line density counts revolution (CPR) with specified optical radius (for rotary encoders). Question What minimum maximum resolutions available with encoder modules? Answer. make encoder modules with resolutions from LPin LPin (1.18 LPmm 14.17 LPmm). Question rotary encoder resolution that standard resolutions? Answer. Custom resolutions obtained ways. standard encoder module design custom codewheel. line density module codewheel must match, optical radius varied make larger smaller diameter codewheel which custom number window pairs. Example: Customer wants encoder, which between HEDS-9100 standard resolutions CPR. Steps: HEDS-9100 #E00 (200 11.00 Rop, LPmm 2.89 lines/mm). Match LPmm module with LPmm codewheel solve optical radius:
LPmm
(Rop)
(LPmm)
(2.89 lines/mm)
12.1
Thus custom codewheel will slightly larger than standard codewheel accommodate extra window pairs (Rop 12.1 11.00 have same line density. modules robust enough handle difference optical radius. other custom resolution have make custom photodetector with desired custom resolution. custom codewheel still required work with custom Contact your local sales representative more information. Question Will codewheel work with encoder module? Answer. line densities module codewheel must match. Thus LPin module will work with LPin module. Question closely does line density codewheel codestrip have match line density module? Answer. modules with less than resolution, general rule thumb that line densities must match within lines/inch module function (0.2 lines/mm). Encoding performance degrades with mismatch thus cannot guarantee encoding specifications when significant mismatch
curs. Question encoder module detect presence absence object? Answer. module looking certain light/dark pattern. passing opaque transparent material past photodetector array cause transition either channel. result predictable.
Mounting
Question encoder module mounting tolerances referenced? Answer. HEDS-9000, 9100, 9200 series encoder modules, tolerances referenced from centers aligning recesses. HEDS9700 series modules, tolerances referenced from aligning post underside module. Question Three channel encoders modules require alignment tool other aligning aid. need alignment tool channel encoders modules?
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Answer. With exception HEDS-9000/9100 Extended Resolution Series, alignment aids required. However, using alignment aids will result better performance recommended. Extended Resolution modules, which HEDS-9000 Options HEDS-9100 Options require alignment aids. some cases, alignment aids also improve assembly times. Question adhesives used instead screws? Answer. Yes. common adhesive used RTV, made Corning 162, Corning 3145) among others. Question What meant "artwork side codewheel?" Answer. artwork side only refers codewheels that made glass mylar (plastic). these codewheels, "art" window/bar pattern appears only side. Generally, better have artwork side closer photodetector array cast cleaner, sharper shadow. With metal codewheels, both sides equivalent since window absence material. artwork side does apply here. Question will between codewheel detector side encoder module affect output? Answer. general, encoders that sensitive codewheel gap. This because lens collimates light into parallel beam keeps light/dark pattern fairly uni-
form. However, codewheel gets closer detector, shadows cast codewheel cleaner sharper. This results better light/dark contrast subsequently somewhat better performance. Question Does provide mounting screws? Answer. Question What TIR? Answer. stands Total Indicated Runout total movement that codewheel window/bar pattern will have radial direction. Thus total eccentricity codewheel. factors which contribute are: Shaft eccentricity Shaft undersize relative Off-center placement relative codewheel Shaft radial play bearing tolerance uneven loading contributes directly cycle error position error encoder. Question bend leads encoder modules? Answer. Yes. standard part numbers HEDS-9001 HEDS-9000 with bent leads), HEDS-9101, HEDS-9041, HEDS9141, HEDS-9701, HEDS-9721. Question remove HEDS-5500 series encoder? Answer. HEDS-5500 series encoders were designed removed. However, possible done carefully. procedure remove
essentially assembly procedure reverse. steps follows: Turn encoder from two-dot position one-dot position. Insert wrench into side hole one-dot mark. Push down wrench, rotate shaft slowly until feel setscrew. Insert wrench into hole loosen setscrew. (This take more than attempt.) Carefully unsnap encoder housing from encoder baseplate. Gently lift encoder housing shaft. housing pulled quickly, codewheel damaged. Remove baseplate screws. Question HEDS-5500 series assembly procedure, Step calls using screwdriver slot turn encoder from one-dot position two-dot position. encoder optional through-hole with screwdriver slot, turn from one-dot two-dot positon? Answer. Insert wrench into side slots encoder housing rotate clockwise from one-dot two-dot positon.
Materials
Question What material encoder module housing? Answer. HEDS-90XX/ 91XX/92XX, material Ryton R-4, polyphenylene sulfide which contains glass fiber. HEDS-9700 series, housing material glass-
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filled polyester with trade name Valox. Question What material HEDS-5500 series housing? Answer. HEDS-5500 series housing also made Valox. Question What lens made Answer. lens polycarbonate. Question What codewheels made Answer. Codewheels made either nickel, nickel-plated copper, stainless steel. hubs made aluminum. codewheel setscrew made black anodized high-carbon steel.
characterized intended such conditions. Customers have tried this also, again with different amounts success. Question Will encoders work fluid? Answer. Fluids ruin optics, potentially cause electrical problems, and, depending fluid, destroy materials encoder. Question well encoders work dusty environment? Answer. encoders fairly robust dusty environments. encoders look multiple sets window pairs. Thus speck dust window will averaged other sets windows bars. Because this averaging effect, number windows covered completely module will still lose count.
minimum high state. outputs sink under Recommended Operating Conditions (3.86 three channel HEDS-9040/9140, HEDS5540/5640). Question trying drive fairly long length cable. What kind additional circuitry should consider? Answer. cable foot range, pull-up resistors Volts each output channel suffice (3.3 channel, three channel). longer lengths cable, either buffer line driver necessary. Question having some problems with noise affecting encoder signals. What should
Reliability
Question there reliability data sheet encoders? Answer. Yes, reliability data sheets available HEDS-9000, HEDS-9100, HEDS9200, HEDS-5500, HEDS-5000, HEDS-6000 series encoders encoder modules. Question Will encoders work vacuum? Answer. encoders characterized were they intended work vacuum. Customers have tried with varying amounts success. Question Will encoders work radioactive environment? Answer. Again, they were
Answer. There several ways improve noise immunity. careful separate motor driver wires from encoder wires, sure Question What solvents separate encoder channels from used clean each other (i.e., twist vicinity encoder with Shielded modules? twisted pair cable recommended encoder lines. Also, sure Answer. found that alseparate ground lines most solvents (besides water) motor/amplifier encoder will attack some part ensince high current switching coder module. This includes motor cause noise alcohols freon-based cleaners. encoder output lines. qualified solvent compatible with encoder Pull-up resistors help somewhat modules. with noise rejection. Additional circuitry, such line drivers/ Electrical receivers optocouplers, much more effective rejecting Question What kind out- noise. really noisy drives encoders environments, additional circuitry have? only totally eliminate noise problem. Answer. encoders have current source output microamps typical, microamps
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Question Does provide line driver outputs? Answer. Yes. made available HEDL-55XX/56XX encoders, which HEDS-55XX/ 56XX encoders with line driver board. This board uses industry standard 26LS31 line driver line driver outputs RS-422 compatible provide complementary outputs inch twisted pair ribbon cable. Both three channel encoders available with line driver option. Contact your local representative further information. Question What meant "push-pull" circuitry? Answer. determining output Channel encoder photodetector looking signals complement These signals sent comparator such that when receives more light than high. receives more light than low. This arrangement called "push-pull" circuitry. advantage that output insensitive variation light level since affected equally light source. Channels configured similarly. Question Typically, much current photodetector draw? Answer. channel modules encoders, typically draws about draws about three channel modules encoders, draws about draws about
Miscellaneous
Question Does provide codestrips? Answer. Only samples. does sell codestrips, provide list codestrip codewheel vendors. Question thick codewheel? Answer. Codewheels between 0.0007 inches (0.018 0.003 inches (0.076 thickness. Question HEDS9000/9100/9200 encoder modules, there metal straps either side five pinouts. What they for? they removed? Answer. These Ground lines which carry current light source. pinouts, where user connects Ground VCC, detector side module. "straps" carry current emitter side module. these lines cut, will light module will obviously function. Question What does "HEDS" stand for? Answer. Hewlett-Packard Emitter Detector System
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This guide answers most often-asked questions about encoders general H

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