Renishaw HS20 Installation Manual page 42

38
Error signal monitoring
WARNING: The HS20 laser encoder continuously checks for any errors that may cause
invalid position feedback signals. This includes an overspeed, beam block, laser unstable
!
or an internal error. It signals a fault by tristating the digital and analogue quadrature lines.
In the case of closed loop motion systems, for safe operation this must be monitored. If the
quadrature is tristated, the position feedback signals may be incorrect and the axis of
motion must be stopped.
NB: In the event of power loss from the HS20 tristated quad will become inactive and the
axis of motion must be stopped.
Status lines
The status lines are all available via the 16-way HS20 interface connector on the HS20, all lines
operate between 24V DC and 0V and are active low. When the lines are unasserted (i.e. at 24V) the
HS20 laser head sources 12mA and when the lines are asserted (i.e. at 0V) the HS20 laser head can
sink up to 600mA. A detailed explanation of each of the status lines is shown below. The status lines
should be monitored so that suitable status messages can be displayed on the controller's display .
Signal Name
/UNSTABLE
/BEAM_BLOCKED
/BEAM_LOW
/OVERSPEED
!
WARNING: If UNSTABLE, OVERSPEED or BEAM BLOCK warning is generated the
machine motion must be stopped.
Function
Indicates that the HS20 laser
head is unstable (or in warm-up).
During this process the quad lines
will remain tri-stated. When the
HS20 laser head becomes stable,
this error will clear automatically.
Indicates that the return signal
strength has fallen below 10% of
full signal strength. Until the error
has been cleared the quad lines
will remain tri-stated.
Indicates that the return signal
strength has fallen below 20% of
full signal strength.
Indicates that invalid quadrature
transitions have been detected.
During this process the signal will
remain tri-stated until the error is
cleared.
Figure 38 - HS20 status lines (machine I/O inputs)
Machine Response
Whilst /UNSTABLE is asserted
low the machine motion must be
disabled.
See safety warning below.
Whilst /BEAM_BLOCKED is as-
serted low the machine motion
must be disabled.
See safety warning below.
Machining can continue, however
the source of the alarm should
be investigated and maintenance
performed.
Whilst /OVERSPEED is asserted
low the machine motion must be
disabled.
See safety warning below.