15.3 The Incremental encoders
An incremental encoder picks up the rotational travel , direction of
rotation, and absolute angular position of a rotating shaft.
One revolution is divided in increments (periods or intervals).
The output signals A and B have about the shape and relationship
shown. An intended irregularity (Nullmarke) is detected, with the
main shaft rotating at constant speed. On detection of the
irregularity, the position counter is set to zero thus providing absolute angular reference to the
shaft.
A
B
Nullmarke
15.3.1 The Incremental encoder at the main shaft
Incremental encoder B8 is located between the ball bearings inside the vibratory tube. It
consists of an annular polygon mirror at the main shaft and the Optoelectronic unit D72.6387,
fastened with a screw M4 to slot in the vibratory tube.
ATTENTION!
To keep dust and light out of the tube, the opening for the Optoelectronic
unit has to be covered with a piece of adhesive tape 30 by 50 mm e.g.
″
Tesa Nr.: 4651
″
(HOFMANN Mat-Nr. 5198320).
In the encoder IC on the Optoelectronic unit, behind a lens there is a red, in the direction of
the main shaft, oblong Light Emitting Diode (LED). Behind a second lens, there are four light
detectors on an integrated circuit.
The light of the LED is reflected back to the encoder by one of the 256 mirrors of the
polygon, focused by the lens on the four detectors. During rotation of the main shaft, the
mirrors will tilt and deflect the light across the detectors A, A`, B and B`. With further
rotation in the same direction, the light will hit the next mirror, and with a full revolution, it
will be deflected 256 times across the detectors in the above given sequence.
The light detectors A and A` respectively B and B` are connected to one amplifier. The
difference in brightness between the detector pairs determines the current state of the output
channels A and B. To keep the signals A and B free from interference, an integrated circuit
amplifies the signals.
An intended irregularity in the arrangement of the mirrors is detected with the main shaft
rotating at constant speed, serving as absolute reference. On detection of the reference, the
position counter is set to zero thus providing absolute angular position of the main shaft.
Checking the incremental encoder is via service code C74.
The surfaces of the 256 polygon mirrors have to be clean and shiny. A dirt particle at the
polygon ring should be removed using adhesive tape. About 20-mm of adhesive tape is put on
a 10-mm wide strip of paper, so that half of the sticky surface extends over the paper. With
the sticky end, the dirt can be picket up without scratching the mirrors.
If the electronic unit fails to detect the zero reference and neither exchanging the
Optoelectronic unit nor cleaning the polygon sleeve proofed successful, the following
measure may help. Turn the main shaft until the solder joint of the code sleeve becomes
visible. Wrap some soft cleaning paper round your forefinger and press the code sleeve
slightly, so it will set in a different way.
The red LED of the reflective encoder IC does not light up immediately after power on, since
voltage is applied under program control!
Is there a defective polygon ring, the complete vibratory assembly has to be exchanged. The
main shaft cannot be removed from the vibratory tube, as the ball bearings are glued-in.
Seite 19 von 99
Summary of Contents for Snap-on Y2k
Page 1: ...SERVICE of the Y2k balancing platform Seite 1 von 99 ...
Page 2: ...The vibratory assemblies of the Y2k balancing platform L R L R S S M Seite 2 von 99 ...
Page 32: ......
Page 35: ...Seite 35 von 99 ...
Page 66: ...Seite 66 von 99 Figure 1 JBEG B9000 B9450 User Interface ...
Page 67: ...Seite 67 von 99 Figure 2 JBEG B9460 User Interface ...
