Xtium2-CXP PX8 User's Manual
Xtium2-CXP PX8 Reference
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49
Shaft Encoder Interface Timing
Dual Balanced Shaft Encoder RS-422 Inputs:
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Input Phase A:
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Connector J7: Pin 3 (Phase A +) & Pin 2 (Phase A -)
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Connector J8: Pin 5 (Phase A +) & Pin 6 (Phase A -)
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Input Phase B:
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Connector J7: Pin 6 (Phase B+) & Pin 5 (Phase B-)
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Connector J8: Pin 7 (Phase B +) & Pin 8 (Phase B -)
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See J7: External I/O Signals Connector (Female DH60-27P) for complete connector signal
details) and J8: Internal I/O Signals Connector (40-pin TST-120-01-G-D).
Web inspection systems with variable web speeds typically provide one or two synchronization
signals from a web mounted encoder to coordinate trigger signals. These trigger signals are used
by the acquisition linescan camera. The Xtium2-CXP PX8 supports single or dual phase shaft
encoder signals. Dual encoder signals are typically 90 degrees out of phase relative to each other
and provide greater web motion resolution.
Example using any Encoder Input with Pulse-drop Counter
When enabled, the triggered camera acquires one scan line for each shaft encoder pulse-edge. To
optimize the web application, a second Sapera parameter defines the number of triggers to skip
between valid acquisition triggers. The figure below depicts a system where a valid camera trigger
is any pulse edge from either shaft encoder signal. After a trigger, the two following triggers are
ignored (as defined by the Sapera pulse drop parameter).
K
D
D
K
D
D
K
D
D
K
D
D
K
D
D
Shaft Encoder phase A
Shaft Encoder phase B
K = Keep
D = Drop or Skip
Note: in this example, Number of trigger to drop = 2
Line acquired
Figure 18: Encoder Input with Pulse-drop Counter
Example using Sequential Encoder Input
Support of a dual phase encoder should consider the direction of motion of one phase signal to the
other. Such a case might exist where system vibrations and/or conveyor backlash can cause the
encoder to briefly travel backwards. The acquisition device must in those cases count the reverse
steps and subtract the forward steps such that only pulses after the reverse count reaches zero are
considered. By using the event “Shaft Encoder Reverse Counter Overflow”, an application can
monitor an overflow of this counter. The maximum count that can be reached by the counter is
returned by the capability CORACQ_CAP_SHAFT_ENCODER_REVERSE_COUNT_MAX. Reading the
parameter CORACQ_PRM_SHAFT_ENCODER_REVERSE_COUNT returns the current count value and
writing any value to this parameter will reset the count to 0.
