Page 742 - Sensors and Systems - North American Catalog
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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
740
Germany: +49 621 776-4411
Refer to General Notes Relating to Product Information
Pepperl+Fuchs Group
USA: +1 330 486 0001
Singapore: +65 6779 9091
Copyright Pepperl+Fuchs
Rotary Encoders
Introduction
Application Notes for Sine/Cosine Rotary
Encoders
Sinusoidal encoders are similar to incremental encoders in that they produce
signals from patterns inscribed on an optical disk. Also like incremental
encoders, they produce two signals that are phase-shifted by 90 degrees.
The difference is that the signals are output as analog sinusoidal waves.
1. Rotational direction monitoring in sine/cosine rotary
encoders
The two sinusoidal signals are phase-shifted by 90 degrees. As with
incremental rotary encoders with square wave output, the direction of
rotation can be determined by evaluating the two signals.
In the top of the figure below (I cw), channel A precedes channel B. This
indicates clockwise rotation. The lower half of the figure (II ccw) shows
counterclockwise rotation.The direction of rotation is determined by viewing
the encoder shaft head-on.
The cycles of the waveforms can be counted and used to determine velocity
or position just like incremental encoders with square wave output. Because
there are no real pulses generated, sine-cosine encoders are rated in cpr
(cycles per revolution).
Unlike incremental encoders, however, the continuous analog voltages can
be used to determine the precise position within each cycle. Also, by reading
the analog voltage value of each channel and performing a mathematical
process called interpolation, the equivalent of thousands of incremental
encoder pulses can be generated for each cycle of the analog voltages.
2. Index signal
The index signal occurs once per revolution at a fixed point and is
transmitted using a third channel (often called channel 0 or Z). The index
signal is usually used as a reference signal for positioning.
On sine/cosine encoders the index signal is also an analog waveform. It
approximates a 90 degree partial sine wave.
3. Interpolation
Incremental encoders with pulse outputs have a practical limit of
approximately 5,000 ppr. Beyond this, the lines on the optical disk are so
fine that controlling the placement and thickness of the lines to ensure
accurate pulse generation is impractical.
To generate line counts greater than 5,000 ppr, sine-cosine waveforms,
like those described above, are generated. By keeping the cpr fairly low
(for instance 1,024 cpr) the accuracy of each cycle can be well controlled.
Interpolation on the sine and cosine waveforms can then be used to
generate pulses at up to 50,000 ppr.
4. Relationship between speed and output frequency
See the operating instructions for incremental rotary encoders.
5. Characteristics of sine/cosine rotary encoders
Because of the continuous nature and simple spectral characteristics
of the sinusoidal output curve of a sine/cosine encoder, there are some
advantages compared to incremental rotary encoders with pulse outputs:
•
Longer cable runs
•
Simple filtering possibilities for cable-coupled interference signals
•
Very low phase jitter
•
Well-suited for monitoring extremely slow speed or “dead stop”
conditions
Application Notes for Absolute Rotary
Encoders
Absolute encoders do not generate pulses, but entire data strings. The
sampling unit in an absolute encoder reads the code disk to determine the
shaft position and the data is transmitted by parallel or serial interface.
Single-turn
In single-turn absolute rotary encoders, each revolution of the encoder
(360°) is divided into a maximum of 65,536 measuring steps (16 bit). After
each complete revolution, the count begins again at the initial value. A single
turn absolute rotary encoder does not count the number of revolutions.
Multi-turn
In addition to the coded disk in a single-turn encoder, a multi-turn encoder
adds a gear that counts up to 16,384 revolutions (14 bit). Overall resolution
amounts to 16 bit (single-turn resolution) plus 14 bit (multi-turn resolution)
for a total of 30 bits of resolution. The resulting 1,073,741,824 measuring
steps can be used to divide very long linear distances into small measuring
steps.
Interfaces
The Pepperl+Fuchs encoder line includes the industry’s largest range of
interfaces for absolute encoders:
SSI-Interface:
The Synchronous Serial Interface (SSI) has been developed to transfer
output data to a controller. The controller sends a bundle of timer pulses
and the absolute encoder responds with the position value.
Parallel Interface:
With a parallel interface, data is sent directly from the Gray-coded encoder
measurement. A parallel interface’s primary advantage is data transfer
speed.
AS-Interface:
AS-Interface uses a multi-slave solution to provide real-time encoder data
transfer.
DeviceNet:
Encoders are available with fully integrated DeviceNet interfaces that
support all DeviceNet functions.
PROFIBUS:
PROFIBUS operation is supported in accordance with Class 1 and Class 2,
and satisfies the PROFIBUS profile for encoders.
CAN:
Pepperl+Fuchs offers encoders with a recessed hollow shaft and solid shaft
design in single- and multi-turn versions. Each model is in accordance with
the CAN standard DSP406 (Class 1 and Class 2).
Ethernet:
These encoders are available with Ethernet TCP/IP interface. The Ethernet
interface is programmable via any web browser.
90
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I cw
II ccw
90
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I cw
II ccw
