Page 736 - Sensors and Systems - North American Catalog
Basic HTML Version
Rotary Encoders
4
Rotary Encoders,
Absolute Rotary Encoders,
Standard
4
.1.1
Rotary Encoders,
Absolute Rotary Encoders
for hazardous areas
4
.1.3
Rotary Encoders,
Absolute Rotary Encoders
for safety applications
4
.1.2
Rotary Encoders,
Incremental Rotary Encoders
with pulse outputs
4
.2.1
Rotary Encoders,
Incremental Rotary Encoders,
Sine/Cosine
4
.2.2
Rotary Encoders,
Incremental Rotary Encoders
for hazardous areas
4
.2.4
otary Encoders,
Incremental Rotary Encoders
for safety applications
4
.2.3
Rotary Encoders,
Safety Speed Monitor
4
.5
Rotary Encoders,
Cable pulls
4
.3
Rotary Encoders,
Accessories
4
.4
734
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Refer to General Notes Relating to Product Information
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Rotary Encoders
Introduction
Technology and Functional Principle
In automation applications, rotary encoders are used as sensors for angle,
position, speed and acceleration. By using spindles, gear racks, measuring
wheels or cable pulls, linear movements can also be monitored by a rotary
encoder. Rotary encoders convert a mechanical rotation value into an
electrical signal that can be processed by counters, tachometers, logic
controllers and industrial PCs.
Rotary encoders use a glass, metal, or plastic disc with alternating
transparent and opaque fields, with a light source on one side and a
light-sensitive sensor on the other. As the disc rotates, the light source
is alternately blocked and revealed to the sensor. Whenever the light
source hits the sensor, the encoder transmits an electric pulse that can be
interpreted by a controller.The pulse ends when an opaque field on the disc
blocks the light source. Rotation of the disc results in a square-wave pulse
output.
0
1
0
1
Most rotary encoders use an infrared light-emitting diode as a light source,
and photodiodes or phototransistors as receivers.
If no other functions are added to the encoder, the only output is a square
wave that indicates that the disc is rotating. The direction of rotation and
absolute position cannot be determined from a square wave output alone.
Therefore, additional components are added to many rotary encoders to
provide additional data about the rotation.
1. Different Functional Principles
1.1 Incremental rotary encoders
Incremental rotary encoders supply a certain number of pulses for each
shaft revolution. Measuring the cycle duration, or counting the number of
pulses during a pre-determined unit of time determines rotational speed.
If the pulses are measured after a reference point is added, the calculated
value represents a parameter for a scanned angle or the distance covered.
Two-channel encoders (those with a phase shift of 90°) enable the
controller to determine the direction of rotation and can enable bi-directional
positioning. Three-channel incremental encoders provide a “zero signal” for
each revolution, giving a fixed point of reference.
For more information, please refer to the section titled “Operating
Instructions for Incremental Rotary Encoders.”
1.2 Absolute rotary encoders
Absolute encoders provide a uniquely coded numerical value for each
shaft position. Absolute rotary encoders eliminate the need for expensive
input components in a positioning application because they have built-in
reference data. In addition, reference runs after a power failure or when the
machine is switched off are not required because the encoder provides the
current position value immediately.
Single-turn absolute encoders divide the shaft into a defined number of
steps. The maximum resolution is 16 bits, which means that up to 65,536
positions can be defined.
By using a multi-step gear, multi-turn absolute encoders not only provide
the angular position within a revolution, but also the number of revolutions.
Multi-turn encoders have a 14-bit resolution to indicate the number of
turns, which means that up to 16,384 revolutions can be identified. Overall
resolution is 30 bits (16 bits per turn + 14 bits for the number of turns) or
1,073,741,824 measuring steps.
Parallel absolute encoders transmit the position value to external analyzing
electronics through multiple wires, one for each bit.
In the case of serial absolute encoders, the output data can be transmitted
by means of standardized interfaces and protocols. In the past, point-to-
point wiring was used for serial data; today, fieldbus systems are becoming
increasingly popular.
For more information on encoder operation, please refer to the section titled
“Operating Instructions for Absolute Encoders.”
2. Different Designs and Mounting
2.1 Rotary encoders with solid shaft
Solid shaft encoders feature a solid drive shaft that must use an additional
coupling to link the encoder shaft to the application’s drive shaft. The
spring-based coupling compensates for misalignment. Belts, pinions,
measuring wheels and cable pulls can also be mounted to the solid drive
shaft. Depending on the type of coupling used, it is important to observe
the maximum shaft load, since excessively high radial or axial forces can
damage the encoder.
Advantages of rotary encoders with solid shaft:
•
Simple construction
•
Higher environmental protection
•
Can be mechanically and electrically disengaged from the application,
depending on the coupling
