Measurement apparatus and method

1. A measurement apparatus for mounting within an enclosure of a machine, comprising;

a measurement device, and

a protection means for protecting the measurement device from contaminants present within the enclosure, the protection means being switchable between at least a first mode that protects the measurement device from contaminants and a second mode that provides less protection of the measurement device from contaminants than the first mode, wherein

the apparatus comprises a contaminant sensor for sensing contamination within the enclosure, the sensed contamination being used to determine when the protection means can adopt the second mode, and

the measurement device comprises an optical tool-setting device having a transmitter for passing light to a receiver along an optical beam path into which a tool to be measured can be inserted.

2. An apparatus according to claim 1 , wherein the apparatus is arranged so that the protection means can only be switched into the second mode when the contamination sensed by the contaminant sensor is below a threshold.

3. An apparatus according to claim 1 , wherein the apparatus is arranged such that the protection means is switched into the first mode when the contamination sensed by the contaminant sensor exceeds a threshold.

4. An apparatus according to claim 1 , comprising a controller for analysing the output of the contaminant sensor and for controlling the protection means.

5. An apparatus according to claim 1 , wherein the measurement device comprises a non-contact measurement device including an optical receiver and/or an optical transmitter, the protection means being arranged to prevent contamination of the optical receiver and/or the optical transmitter.

6. An apparatus according to claim 1 , wherein the protection means comprises at least one shutter for protecting the measurement device, the shutter providing a larger aperture in the second mode than in the first mode.

7. An apparatus according to claim 1 in which the measurement device comprises a measurement sensor, wherein a single sensor provides both the measurement sensor and the contaminant sensor.

8. An apparatus according to claim 1 , wherein the measurement device includes a measurement sensor that is different to the contaminant sensor.

9. An apparatus according to claim 1 , wherein the contaminant sensor is an optical sensor that analyses received light that has passed to the optical sensor through a region within the enclosure.

10. An apparatus according to claim 1 , wherein the measurement device, the protection means and the contaminant sensor are provided within a single measurement unit.

11. An apparatus according to claim 1 , wherein the measurement device and the contaminant sensor are provided as a plurality of separate units.

12. An apparatus according to claim 1 , wherein the measurement device can acquire object measurements when the protection means is in both the first and second modes.

13. An apparatus according to claim 1 , wherein the protection means can also adopt at least one additional mode.

14. A method for operating a measurement apparatus mounted within the enclosure of a machine, the measurement apparatus comprising (a) a measurement device that includes an optical tool-setting device having a transmitter for passing light to a receiver along an optical beam path into which a tool to be measured can be inserted and (b) a protection means for protecting the measurement device from contaminants present within the enclosure, the protection means being switchable between at least a first mode that protects the measurement device from contaminants and a second mode that provides less protection of the measurement device from contaminants than the first mode,

wherein the method comprises the steps of:

(i) sensing an amount of contamination within the enclosure, and

(ii) determining when the protection means can adopt the second mode based on the amount of contamination sensed in step (i).

15. A measurement apparatus for mounting within an enclosure of a machine, comprising;

a measurement device, and

a shutter for protecting the measurement device from ingress of contaminants present within the enclosure, the shutter being switchable between at least a first mode that protects the measurement device from contaminants and a second mode that provides less protection of the measurement device from the ingress of contaminants than the first mode, the shutter providing a larger aperture in the second mode than in the first mode, wherein

the apparatus comprises a contaminant sensor for sensing contamination within the enclosure, the sensed contamination being used to determine when the shutter can adopt the second mode.

16. A measurement apparatus for mounting within an enclosure of a machine, comprising;

a measurement device, and

a protection means for protecting the measurement device from contaminants present within the enclosure, the protection means being switchable between at least a first mode that protects the measurement device from contaminants and a second mode that provides less protection of the measurement device from contaminants than the first mode, wherein

the apparatus comprises a contaminant sensor for sensing contamination within the enclosure, the sensed contamination being used to determine when the protection means can adopt the second mode, and

the measurement device comprises a measurement sensor, wherein a single sensor provides both the measurement sensor and the contaminant sensor.