Geometrical instruments – Gauge – Having a movable contact probe
Patent
1989-10-16
1991-08-20
Haroian, Harry N.
Geometrical instruments
Gauge
Having a movable contact probe
33503, 33558, 33561, G01B 2122, G01B 500
Patent
active
050403060
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a surface-sensing device for use in position-determining apparatus such as, for example a coordinate measuring machine or machine tool.
Such a machine is used for measuring a workpiece, and typically comprises a head moveable in three directions x, y, z, relative to a table on which the workpiece is supported. Movement of the head in each of the directions relative to a datum provided on the table is measured by scales on the machine, and a probe provided on the head emits a signal indicating the relationship between the workpiece surface to be measured, and the head. The position of the surface may thus be determined.
It is sometimes desirable to obtain continuous data on the position of a surface, i.e., to scan the profile of a surface with the machine, rather than simply obtain data in the form of one or more discrete points.
2. Description of Related Art
To achieve this, a measuring probe is provided on the head. The probe supports a stylus for movement relative to the head, and measures the magnitude of the stylus movement relative to the head in the x, y, z directions. The head may therefore move adjacent the surface to be scanned while the stylus is in contact with the surface, and the surface profile may thus be determined. An example of such a probe is shown in U.S. Pat. No. 3,869,799.
SUMMARY OF THE INVENTION
The present invention provides a surface sensing device for use on a head of a coordinate positioning machine, the device comprising:
an elongate stylus;
first supporting means for supporting the stylus for one-dimensional movement along a linear axis parallel to the length of the stylus;
second supporting means for supporting the stylus for rotation about a first rotational axis extending substantially perpendicular to the length of the stylus; and
a motor for rotating the stylus about the first rotational axis in response to a control signal.
BRIEF DESCRIPTION OF THE DRAWINGS
An example of apparatus according to this invention will now be described with reference to the accompanying drawings wherein:
FIG. 1 is a partly sectioned elevation of a probe head.
FIG. 2 is an elevation of a coordinate measuring machine embodying the probe head.
FIG. 3 is a system diagram showing a computer arranged for controlling electrical components of the machine and the probe head.
FIG. 4 is an perspective view of a workpiece whose contour is to be determined by the machine and probe head.
FIG. 5 is an elevation of the workpiece.
FIG. 6 is a plan view of FIG. 5.
FIG. 7 is a section on the line VII--VII in FIG. 6.
FIG. 8 is a section on the line VIII--VIII in FIG. 6.
FIG. 9 is a diagram of a control system for controlling the machine and probe head for the purpose of a scanning operation.
FIG. 10 is a detail of FIG. 1 and shows a modification of a motor shown in FIG. 1.
FIG. 11 is a view similar to FIG. 5 and diagrammatically illustrates deflection of the probe head.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, an elongate stylus 10 extending along an axis 10A has a spherical sensing element 11 whereby to engage a surface 12A of workpiece 12 whose contour is to be determined. Two planar springs 13,14, secured between a housing 15 and the stylus 10 support the stylus for linear displacement over a distance D1 relative to the housing 15 in the direction of the axis 10A. A motor M1 arranged between the housing 15 and the stylus 10 is adapted for applying a force F1 to the stylus in the direction of the axis 10A and a transducer T1 is provided for sensing the axial position of the stylus relative to the housing 15. The motor M1 is an electromagnetic positioning device urging the stylus in a sense away from the housing 15. A strain gauge system 16 provided on the stylus 10 is adapted for sensing any force F2 on the element 11 in a direction transverse to the axis 10A. The forces F1,F2 are assumed to act through a point B being the centre of the spherical element 11. The output of the system 16 is denoted S and
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McMurtry David R.
Powley David G.
Haroian Harry N.
Renishaw plc
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