ACR2 autochange rack

The ACR2 autochange rack is an arm-changing system for the PHS1 servo positioning head.  It allows probe extensions or probe adaptors to be exchanged to suit the probing task required.

Arms are locked or unlocked from the head by motion of the machine itself.  The head engages a rack port and the machine drives the port up to unlock an arm or down to lock it in position.

No power connections or signal connectors are necessary to the rack, making installation very simple.

The ACR2 is supplied as pairs of rack ports which are mounted onto a suitable fixture supplied by the OEM.  The system is modular and any number of port pairs can be used anywhere on the CMM.

System features

Modular construction

Ports can be positioned in pairs anywhere on the machine.

Simple concept

The change cycle is operated by CMM motion. No power connections are needed and all sensing and overtravel protection is contained within the PHS1 servo positioning head itself; no motors, switches or sensors within the rack.

Expandable concept

Any number of racks can be fitted anywhere on the machine, for example a four port rack at one end and a two port rack at the other.

Versatile probing

ACR2 ports can accommodate touch-trigger, analogue contact or laser scanning probes, with or without extension bars.

Safe operation

Sensors on the PHS1 servo positioning head detect collisions and check whether arms are correctly and safely locked in position after a change cycle. The PHS1 also incorporates an overtravel mechanism to protect against collisions.

Sealed arm locations

Covers with effective seals protect electrical contacts and kinematic locations when not in use.

System description

The ACR2 rack consists of pairs of ports that store arms. The arms are either head adaptors (HA) or head extensions (HE).

The ports allow arms stored in them to be automatically locked and unlocked onto a PHS1 servo positioning head.

To change probe arms automatically, the CMM must be programmed to complete a series of movements using positions calculated during the port datum routine.  These movements cause a mechanism inside the port to rotate a screwdriver which engages a slot on the arm. The slot activates a cam which locks the arm in place when rotated.

Manual fitment of probe arms can be achieved using the S10 autojoint key supplied.

Arms are located in the rack port on two steel pins which pass through holes in the arm.  A spring-loaded lid secures the arm in position and seals the spring-loaded electrical contacts and kinematic locations against contamination.

Signals are provided by the servo positioning head to indicate when an arm is present and whether the arm is locked correctly and safely.  This ensures that arms are always positively locked on the head.

Crash protection is provided by the head overtravel unit.  Any machine move errors or mis-programmed moves which cause an unexpected collision will cause the head overtravel to operate, sending a signal to stop the machine.

NOTE: The maximum operating speed of the ACR2 autochange rack should not exceed 100 mm/s.

The following figure shows an example of a six-port ACR2 installation.

NOTE: The mounting pillar is not supplied by Renishaw.

Six-port ACR2 installation:

Six-port ACR2 installation