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4
Introduction
The Renishaw HS20 laser head provides linear position feedback for machine tools using laser
interferometry. The HS20 laser head has been designed to be rugged and reliable whilst operating 24
hours a day in a machine shop environment. Depending on the application, the HS20 laser head may
be connected directly to a motion control system, alternatively it may be connected via the RCU10
quadrature compensation unit. In case of the latter, please also refer to the RCU Manual (M-9904-
1122) which provides extensive information on system integration. Always refer to the manual for
information on the HS20 laser system.
This manual is separated into chapters to cover the standard installation of the HS20 laser system.
The chapters cover mechanical and electrical installation and integration of the system in the machine
controller. The appendices give further instruction on alignment diagnosis and system troubleshooting.
!
WARNING If this equipment is used in a manner not specified by the manufacturer, the
protection provided by the equipment may be impaired.
General safety information
The Renishaw HS20 laser encoder and compensator systems are designed for integration into the
primary position feedback loop of a motion system. It is essential that the system is installed in
accordance with the instructions in the installation manuals and it is the responsibility of the system
integrator to ensure that, in the event of a failure of any part of the Renishaw laser system, the motion
system remains safe.
In motion systems with powers or speeds capable of causing injury, safety protection measures must
be included in the design. It is recommended that satisfactory operation of these protection measures
is verified before the feedback loop is closed. The following are examples of safety protection
measures that can be used. It is the sole responsibility of the system integrator to select appropriate
measures for their application.
1. The HS20 quadrature will go into a tristate condition (open circuit) under fault conditions. The
equipment receiving this quadrature (RCU or machine controller) must detect the tristated
condition and stop the axis moving. All status lines should be connected so that the HS20
condition is monitored and the following actions should be initiated:
- /UNSTABLE - Whilst /UNSTABLE asserted low, the machine motion must be disabled.
- /BEAM_BLOCKED - Whilst /BEAM_BLOCKED is asserted low, the machine motion must be
disabled.
- /BEAM_LOW - Machining can continue, however the source of the alarm should be
investigated and maintenance performed.
- /OVERSPEED - Whilst /OVERSPEED is asserted low the machine motion must be disabled.
2. The axis must include physical limit switches which, when tripped, will stop axis motion before
damage occurs (soft limits alone are insufficient). Note that in the case of thermally compensated
systems, positional corrections of several hundred ppm are possible. This should be taken into
account when defining the relative positions of soft and hard axis limits.
3. Cable breakage detection (encoder disconnect). The position feedback is provided as differential
line driven pairs. Failure in the cable or of the line drivers can be detected by checking these
differential pairs are always being driven in opposing states. If the lines are not in opposing
states, the motion must be stopped.
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