Renishaw RCU10, Installation And User Manual, Page: 4 / 202

General safety notice i
General safety notice
The Renishaw 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 guide and it is the
responsibility of the system integrator to ensure that, in the event of a failure of any part of
the Renishaw system, the motion system remains safe.
In the case of motion systems with powers or speeds capable of causing injury, it is
essential that appropriate safety protection measures are included in the machine design.
Further guidance on this can be found in the European Standard EN292 “Safety of
machinery – Basic concepts, general principles for design”. It is the sole responsibility of
the OEM/system integrator to select the safety measures appropriate for their application.
The following is a list of measures that should be considered as part of that process.
1. The Renishaw system includes an Error signal output. The control system must be
designed to stop the axis motion if this error output is asserted. In addition to the
Error signal, the position feedback signals can also be configured to go tristate
(open circuit) under fault conditions. Some controllers can be programmed to detect
this, thereby providing a further level of protection in case of failure of the error
signal output (see item 3 below). If the controller is not capable of detecting open
circuit position feedback signals, this option must not be enabled.
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
failure of the line drivers can be detected by checking that 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, then 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, then the axis motion
must be stopped.