ENCODER

Encoders provide motion control systems information on position, count, speed, and

direction. As the encoder shaft rotates, output signals are produced, proportional to the

distance (angle) of rotation. The signal may be in the form of a square wave (for an

incremental encoder) or an absolute measure of position (for an absolute encoder).

Due to the performance and reliability advantages of the semi-conductor technology they

incorporate, optical encoders are the preferred solution in many common computer, industrial,

and automotive applications. Optical encoders also benefit from ease of customization, are

suitable to numerous environments, and suffer no effects from high levels of stray magnetic

fields.

The basic construction of an incremental encoder is

shown to the right. A beam of light emitted from an LED

passes through a transparent disk patterned with opaque

lines, and is picked up by a photodiode array. The

photodiode array (also called a photosensor) responds

by producing a sinusoidal waveform which is transformed

into a square wave, or pulse train.

Incremental encoders are available in two basic output types, single channel and quadrature.

A single channel encoder, often called a tachometer, is normally used in systems that rotate

in one direction only, and require simple position and velocity information. Quadrature

encoders have dual channels (A and B), phased 90 electrical degrees apart. These two

output signals determine the direction or rotation by detecting the leading or lagging signal

in their phase relationship. Quadrature encoders provide very high speed bi-directional

information for very complex motion control applications.

Incremental encoders can provide a once-per-revolution pulse (often called index, marker, or

reference) that occurs at the same mechanical point of encoder shaft revolution. This pulse

is on a separate output channel (Z) from the signal channel or quadrature outputs. The index

pulse is often used to position motion control applications to a known mechanical reference.

Resolution is a term used to describe the Cycles Per Revolution (CPR) for incremental

encoders, or the total number of unique positions per revolution for an absolute encoder.

Each incremental encoder has a defined number of cycles that are generated for each full

360 degree revolution. These cycles are monitored by a counter or motion controller and

converted to counts for position or velocity control. Absolute encoders generate a unique

code word for every resolvable shaft angle (often called bits or counts per revolution).

Encoder accessories.

Accessory items are often the difference between an installation that goes smoothly, and one

that does not. EPC offers a range of accessories that are designed to not only make your

life easier, but are manufactured to EPC’s high standards, ensuring years of trouble free

service. In addition, they have been tested with the products they complement, so that you

do not have to worry about proper form, fit, or function.

Connectors/Cables

High quality connectors, cables, cable assemblies, and cord sets

selected to optimize encoder performance; most can be ordered

with MS style or M12 connectors.

Shaft Couplings

Precision shaft couplings to optimize performance and reduce the

chance of premature failure; designed to restrict the transfer of

thermal and mechanical stress; wide range of choices to match your

exact requirement. Call about our new Magnetic Coupling!

Protective Covers

Covers help protect encoders from damage. They also allow a wider

variety of encoders to be used in harsh environments.

Hub/Flanges

Allow Accu-CoderTM encoders to be easily mounted to industry

standard housing styles; NEMA, servo, 5PY, and other styles

available; rugged, reliable construction

Mounting Brackets

Used to mount measuring wheels to Cube and 702 Series

Accu‑CodersTM. Two types: single pivot and dual pivot; single pivot

pivots vertically while dual pivot pivots vertically and longitudinally.

Measuring Wheels

Used to obtain linear motion feedback from a rotating shaft; range of

surface finishes (urethane, rubber, knurled, grooved) for proper

mating to nearly any application surface; available in several sizes

to allow you to satisfy your exact requirements.

Linear Cable Adapter

The linear cable adapter (LCA) used with a Cube Series standard or

industrial housing, provides a low cost alternative for obtaining

accurate linear measurement.

MOUNTING AND MECHANICAL INSTALLATION

For over 40 years, our engineers have been designing encoders that are quick and easy to

install. With a variety of mounting options available, your encoder should be a perfect match

for your existing equipment. Accessories such as pivoting mounting brackets, measuring

wheels, flexible couplings, etc., are available from EPC to ease installation.

The first principle for every encoder installation is "Don't force it!". Striking or using

excessive force can either damage your new encoder, or introduce excessive shaft loading,

shaft misalignment, or other conditions shortening its expected life. Tighten all couplings and

bolts to their recommended torque. Remember, tighter isn't always better!

Shaft Style Encoders

Gently couple the shaft of the Accu-CoderTM to the driving

shaft, using a correctly sized flexible shaft coupling.

Never use a rigid coupling.

• Verify proper alignment between the Accu-CoderTM shaft

and the driving shaft.

• If using pulleys or gears, mount them on the shaft as close

as possible to the Accu-CoderTM to reduce bearing load.

• Axial and radial shaft loading should be low as possible.

Never exceed printed specifications.

• Use recommended torques to tighten all clamping bolts and

couplings.

Hollow Bore Encoders

• Make sure driving shaft is free from burrs and other defects.

• With flex mount flush against surface, tighten clamp or set

screws first, then bolt flex mount to surface.

• Check for best possible alignment with hollow shaft and

driving shaft to reduce wobble.

• Runout of the driving shaft, or misalignment between the

driving shaft and the encoder’s hollow bore, decreases the

accuracy and bearing life of the encoder and adds vibration

to the system. Re-installing the encoder on the driving shaft

may improve alignment.

C-Face Style Encoders

• Verify that mounting holes are in exact alignment with holes

or studs on the motor frame.

• Tighten all fasteners with equal torque so as not to distort the

shape of the ring

.

ELECTRICAL CONNECTION

Proper wiring and grounding are essential for the longevity and proper operation of your

Accu-CoderTM . In addition, electrical noise should be minimized to prevent improper counts

and/or damage to the electronic components.

Since an Accu-CoderTM can be used with a wide variety of input devices (PLC’s, counters,

servo controllers, etc.), from many different manufacturers, it is important to determine proper

wiring and connections before installation.

Common Signals

Most Accu-CoderTM encoders have the following electrical connections:

Power, Common or Ground, and one or more Output Signals.

Power (Also called supply, power source, encoder power, +V, or +VDC)

• Always use a direct current (DC) voltage.

• Attach power to the positive (+) side of the power source.

• Verify that the Accu-CoderTM is receiving the proper voltage, since most electrical

failures are caused by an improper or improperly regulated power source.

• The use of surge protection is highly recommended.

Common (Also called Com, supply common, and ground)

• Attach common to the negative (-) side of the power source.

Output Signals (Always at least one, but may be as many as six)

• The most common are A, B, and Z. Commutation outputs include U, V, and W.

• Encoders with a Line Driver output also have the complement (A and A’, B and B’,

etc.) as separate outputs that are used to provide differential signals for reduced

noise and greater drive capability.

• Never connect the output signals together, or to the power source!

Connections

• Verify and match up pin numbers, wire colors, or terminal blocks with the input device.

• Be aware that identification terminology may not always be identical.

• Once proper wiring is determined, document it for future reference.

Cable Routing

• Cable length should be minimized by using the shortest route possible.

• All cabling should be installed in dedicated metal conduits, or located at least 12” away

from other wiring.

• Route cables away from high current conductors to minimize pulses caused by

electrical transients.

• Signal wire continuity should be maintained from the encoder to the controller/counter.

Avoid junctions and splices, if possible

Radiated Electrical Noise

• Noise can be generated by solenoids, relays, motors, starters, and similar devices.

• Using shielded cables will dramatically reduce the effects of noise. Most Accu-CoderTM

cables are double shielded (foil and braid) for optimum protection.

• Ensure all equipment is properly grounded. (Motors, drives, shafts, etc.)

• Connect encoder cable shield to ground at controller/counter end, leaving the end near

the encoder unconnected. Connecting the shield at both ends can cause ground loops,

and improper operation.

• If possible, use differential line driver outputs with high quality shielded, twisted

pair cable. (Complementary signals greatly reduce common mode noise levels, as well

as signal distortion resulting from long cable lengths.)

• EPC’s line of Repeaters and Converters may help reduce the effects of electrical noise.

TROUBLESHOOTING

No Output/No Counts

• If there is no mechanical movement, there will be no output. Therefore, verify that the

Accu-CoderTM is rotating.

• Check to make sure the proper supply voltage is present. It is best to do this at the

Accu-CoderTM end, if possible.

• Verify all wiring between the Accu-coderTM , the counter/controller, and the power supply.

• Make sure that the proper signal type (OC, PU, LD, PP) is being used for the

application.

• Verify that the counter/controller is properly installed and operational. Consult the

appropriate User’s Manual if necessary.

• If another Accu-CoderTM is available, try it to determine if the encoder is the problem.

Erratic Output/Missing or Extra Counts

• Electrical: Check for loose wiring connections, ground loops, encoder outputs

incompatible with the counter/controller, a noisy power supply, electrical noise, proper

termination of shields, or a combination of these problems.

• Mechanical: Check for improper alignment, loose coupling, or, if used, slippage in the

measuring belt or wheel.

Counts Indicate Wrong Direction

• Check for reversed wiring of the quadrature signals. Reverse if needed.

• If differential signals are being used, make sure that both sides are properly wired.

• Note: If an index pulse is being used, reversing the wiring will cause the

reference alignment to change.

Counts In Only One Direction

• Make sure that the counter/controller is capable of, and programmed for, bi-directional

counting.

• On quadrature units, both channels (A and B) must be present and operational. Check

by using a dual channel oscilloscope.

• Make sure the input selection type programmed into the counter/controller, matches the

Accu-CoderTM . If there is a mis-match, the system may not work properly.

Index Pulse Not Working

• The index pulse occurs only once per revolution, and can be difficult to check with a volt

meter. Check index pulses with an oscilloscope.

• The counter/controller may not be capable of detecting the index pulse at higher RPM’s.

Slowing down the rotation may allow for detection of the index pulse.

• Verify wiring.