The Renishaw servo positioning head (PHS1) is a two-axis motorised head with ±184° servo drive enabling the probe configuration to be positioned at almost any angle. This makes the head ideal for use in restricted spaces and enables styli to be angled normal to a surface or aligned to the axis of a hole.
The head can carry multiple probing types and very long extensions, making it highly suitable for measurement of large complex parts.
Movement and positioning of the head is co-ordinated directly by the CMM controller, allowing the motion of the head to be synchronised with the motion of the machine's axes for maximum component accessibility and minimum cycle time.
Further sections of this guide give general descriptions of the PHS1 system components.
Two-axis servo positioning head
The two servo axes (D and E) are functionally identical and feature:
- Backlash-free motor/gearbox units
- Precision mechanical bearings
- High-accuracy, high-resolution angular measurement system for positional feedback
- Reference marks to give axis position on start-up
- Velocity control loops that keep the angular velocity of the axis constant at the commanded value regardless of load
- A high-speed serial link that receives commands from, and transmits status information back to, the interface card
During measurement cycles the head does not drive to a locked, repeatable position in the same way as an indexing head. Instead the CMM controller drives the probe tip to the desired position. When a probing point is taken, the respective axes of the head and CMM are latched simultaneously to give accurate probe readings.
The head can hold its position or can be used in a continuous mode whereby it is servo driven continuously to follow a pre-programmed path.
Coloured LEDs on the head overtravel cap indicate probe and head status:
- The green LED indicates power is being supplied to the PHS1 probe head
- The red LEDs are positioned on each face of the overtravel cap and indicate when the probe has been triggered
An air supply to the head is required for axis motor cooling to give optimum metrology performance.
Overtravel protection unit
The PHS1 head includes a built-in spring-loaded overtravel unit for protection of both head and CMM in the event of a collision between the head and workpiece or CMM itself.
The features of this overtravel unit include:
- Optional electronic overtravel signalling - configured by the CMM manufacturer
- Generous overtravel limits allowing machine motion to be stopped before damage is caused - providing electronic stop is configured
- Automatic reset on kinematic locations once any obstruction has been cleared
- Flexible bellows seal
Probe arms can be exchanged to allow the use of a wide range of different probe types and configurations.
Automatic arm exchange on repeatable kinematic locations is available using the ACR2 autochange rack.
Touch trigger probes can be used to reach up to 750 mm.
Signals are made available to the PC interface card to indicate that an arm is fitted and that the arm is locked safely into position.
PC interface card
The head is controlled from the PC interface card in the CMM controller, or directly from the CMM controller. This card handles communications and conditions signals between the head and the CMM controller and also provides power supply to the head axis drives.
The PC interface card does not handle probing system signals.
Further information is given in the PHS1 programmer's guide (Renishaw part number H-1000-6005) and the PHS1 installation guide (Renishaw part number H-1000-4044).
ACR2 autochange rack
The ACR2 autochange rack is an arm-changing system for the PHS1 servo positioning head system. It allows probe extensions or probe adaptors to be exchanged to suit the probing task required without manual intervention. Its modular construction and simple operation enable any number of racks to be positioned anywhere within the machine volume. Each rack is configured from pairs of rack ports which are mounted to a vertical pillar (not supplied by Renishaw).
Further information is given in the ACR2 installation guide (Renishaw part number H-1000-4045).
Custom versions are available to mount horizontally when PHS is mounted vertically.