688
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
Rotary 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
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Consider the General Notes on the Information in the Pepperl+Fuchs Product Catalogs
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Copyright Pepperl+Fuchs
Technology and Functional Principle
Rotary encoders are used in automation technology as sensors for an-
gles, positions, speed, and acceleration. Spindles, gear racks, measuring
wheels, or cable pulls can also be used to detect linear movements.
They convert the actual value of a mechanical movement into electric
signals that can be evaluated by counters, tachometers, PLCs, and in-
dustrial PCs.
Transparent and nontransparent fields are applied to a plastic or glass
pane.
Placing a light source on one side of the pane and a light receiver on the
other enables rotation to be detected in a noncontact manner. If the light
beam hits a transparent field, the receiver circuit detects a pulse. How-
ever, if the path of the beam is interrupted by a dark field, no pulse is trig-
gered. LEDs that emit light in the infrared range are usually used as the
light source. Photo diodes or photo transistors are used as the receiver.
0
1
0
1
If no further functions are added to this principle, the device simply de-
tects that the disk is rotating. It is not possible to specify the direction of
rotation or even an absolute position.
Rotary encoders differ in terms of their functional principle, mechanical
design, and mounting.
1.
Different Functional Principles
1.1
Incremental rotary encoders
Incremental rotary encoders provide a defined number of pulses per
shaft revolution.
The speed of a movement is determined by measuring the period dura-
tion or counting the pulses per time unit. If you add together the pulses
from a reference point, the counted value represents a measurement for
the angle passed or the distance traveled.
Two-channel rotary encoders–with 90° phase-shifted output signals–en-
able the downstream electronics to determine the direction of rotation of
the shaft and thereby also enable bidirectional positioning tasks.
Three-channel incremental rotary encoders issue a zero signal once per
revolution.
For further information, see the section "Application Notes for Incremen-
tal Rotary Encoders."
1.2
Absolute rotary encoders
Absolute rotary encoders output a uniquely coded numerical value at
each shaft position.
For positioning applications in particular, absolute rotary encoders per-
form the counting tasks instead of the subsequent electronics, eliminat-
ing the need for complex and expensive input components. Furthermore,
reference runs do not need to be performed when switching the machine
on or if the supply voltage fails, because the current position value is
available immediately.
Singleturn absolute rotary encoders divide one shaft revolution into a de-
fined number of measuring steps.The maximum resolution is 16 bits, i.e.,
up to 65,536 different positions.
Multiturn absolute rotary encoders do not just detect angular positions
within a revolution, they also detect the number of revolutions using a
multistage gear. The resolution of the multiturn part is up to 14 bits, i.e.,
up to 16,384 revolutions can be identified.This results in a total resolution
of 30 bits or a total of 1,073,741,824 measuring steps.
Parallel absolute rotary encoders transfer the position value to the evalu-
ation electronics in parallel over several lines.
In the case of serial absolute rotary encoders, the output data is issued
via standard interfaces and standardized protocols. Point-to-point con-
nections were often used in the past to perform a data transfer, whereas
nowadays fieldbus systems are increasingly used.
For further information, see the section "Application Notes for Absolute
Rotary Encoders."
2.
Different Designs and Mounting
2.1
Rotary encoders with solid shaft
These rotary encoders are fitted with a solid shaft. The rotary encoder is
connected to the drive shaft via an additional coupling.The coupling con-
nects both shafts mechanically and compensates the axle offset.
Straps, pinions, measuring wheels, and cable pulls can also be used to
connect a rotary encoder to the driving shaft.
Generally, attention must be paid to the permissible shaft load. Depend-
ing on the coupling type, there are different levels of risk of destroying the
measuring device due to radial and/or axial forces that are too strong.
Advantages of rotary encoders with solid shaft:
•
Simple construction
•
Higher degree of protection possible
•
Mechanically and, depending on coupling, also electrically decoupled
Disadvantages of rotary encoders with solid shaft:
•
Many parts for mounting the rotary encoder: rotary encoder, mounting
flange, coupling
Rotary Encoders
