US 5,208,993 AGranted

Touch probe

AssigneeRenishaw Metrology Limited

InventorAndrew J. Harding

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Abstract

A touch probe (10) has a housing (12) and stylus-supporting member (14) biased into a kinematic rest position relative to the housing (12) by a biasing mechanism. The biasing mechanism includes a first helical spring (40) which acts between a movable shuttle (44) and an intermediate member (48). The shuttle (44) is movable within a bore (46) and the position of the shuttle within the bore may be adjusted by the action of an adjusting screw (74). A second helical spring (42) acts between intermediate member (48) and the supporting member (14). The first spring (40) has a low spring rate and is pre-loaded such that the second spring (42), which has a high spring rate, will deflect first upon movement of the shuttle (44) or supporting member (14). Once the pre-load of spring (40) has been overcome the two springs (40,42) co-operate to act as a single spring whose spring rate is the sum of the reciprocals of the spring rates of springs (40,42). This provides adjustment of the biasing force with only a small movement of the shuttle (44) while simultaneously providing large deflections of the stylus-supporting member (14) opposed with a low rate of increase of biasing force.

Claims7

Dependent claims

A touch probe for use on a coordinate positioning machine, comprising:

a fixed structure by which the probe may be supported on a movable arm of the machine;
a stylus-supporting member supported relative to the fixed structure in a repeatable rest position from which the supporting member may be displaced under the influence of a deflecting force and to which the supporting member may return when the deflecting force is removed;
and
biasing means for urging the supporting member into said rest position, said biasing means comprising a first biasing element acting between an abutment provided on the fixed structure and an intermediate member, and a second biasing element acting between the intermediate member and the supporting member;
adjusting means for adjusting a biasing force provided by said biasing means on said supporting member comprising means for adjusting a distance between said abutment and said supporting member;
wherein
the intermediate member is movable relative to both the abutment and the supporting member;
and
the first and second biasing elements have different spring rates, the biasing element with the lower spring rate being pre-loaded so that adjustment of said distance initially causes a change in the load applied to the supporting member at a rate of change of force with change of said distance which corresponds to the spring rate of the biasing element having the higher spring rate.

6 more elements

Dependencies are inferred from the claim text.