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APPENDIX D - Safety information
The following appendix covers important safety information, which should be read before installing or
operating any part of the laser scale system.
It is the responsibility of the manufacturer and/or encoder installation authority to ensure that, in safety
critical applications of the HS20 laser encoder, any form of signal deviation from specification or
from the limits of the receiving electronics, however caused, shall not cause the machine to become
unsafe. It is also their responsibility to ensure that the end user is made aware of any hazards involved
in operation of their machine, including those mentioned in Renishaw product documentation, and to
ensure that adequate guards and safety interlocks are provided.
When mounting and using Renishaw laser encoder products on machines, beware of pinch and/
or crush hazards that can be created depending on how and where the equipment is mounted. This
warning is particularly relevant to the mounting of the optics
General safety information - system integration
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 faulty conditions. All
status lines must also be connected. The control system must be designed to stop the axis
motion if this error output is asserted.
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 and error signal lines
are all 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.
4. Motor torque monitoring. If the motor torque exceeds an expected limit, the axis of motion must
be stopped.
5. The machine must include an emergency stop button.
6. Following error detection. If the difference between the controller demand position and the axis
feedback position exceeds an expected limit, the axis motion must be stopped.
7. Guards, viewing windows, covers and interlocks may be used to prevent user access to
hazardous areas, and to contain ejected parts or materials.
8. If the machine includes an independent tacho (velocity) feedback system, this should be cross-
checked with the position feedback. For example, if the tacho indicates the axis is moving, but
the position feedback doesn't, the axis motion must be stopped.
9. In the case of synchronised parallel motion systems (for example twin rail gantry drive systems),
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