Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1995-06-27
1997-02-18
Epps, Georgia Y.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
409235, 409178, 409179, 248371, G01B 902
Patent
active
056045930
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to machines in which one support or platform is supported and moved relative to another by a plurality of extensible legs or rams extending between them. There may be, for example, three or six such legs or rams, and when there are six the machine is commonly called a hexapod. Such arrangements may be used for machine tools, coordinate measuring machines, scanning machines, robots, positioning devices (e.g. for optical components), flight simulators, prototype manufacturing machines and various other uses.
BACKGROUND OF THE INVENTION
International Patent Application No. WO91/03145 (Kearney & Trecker) shows a hexapod machine tool comprising two supports or platforms and six extensible, powered legs or rams, each connected between the two supports or platforms. A tool on one of the platforms is movable relative to a workpiece on the other platform. Various desired positions and orientations between the tool and the workpiece can be achieved by extending the legs by differing amounts.
In such machines, the position and orientation at any instant is monitored by means of a plurality of length measuring transducers, e.g. one transducer associated with each leg. WO91/03145 discloses the use of six instrument arms, separate from the legs, each instrument arm containing a length measuring transducer. One possible type of length measuring transducer is a laser interferometer in each instrument arm. Taking six length measurements from the six instrument arms enables the position and orientation of one platform relative to the other to be determined. In practice, such length measurements are used in a feedback loop to the powered legs, to servo the movable platform precisely to the position and orientation required.
The instrument arms disclosed in WO91/03134 require a universally pivotable bearing at each end, to connect the arm to the respective platform. Therefore, if there are any inaccuracies such as backlash in these bearings, the measured lengths will be inaccurate and there will be a corresponding inaccuracy in the positioning and orientation of one platform relative to the other.
SUMMARY OF THE INVENTION
The present invention provides a machine comprising: the position and orientation of one support structure relative to the other being defined by the relative lengths of the extensible legs; comprising a light emitting unit associated with one support structure and a reflector associated with the other support structure; support structure.
Preferably the light emitting unit is directed towards the corresponding reflector by a mechanical linkage connected to one of the extensible legs, or which itself forms an extensible leg, connected between the support structures.
In another aspect of the invention, there is provided an interferometer for use in such a machine, comprising: the machine; the machine; and said support structures, or itself forming such an extensible leg, for directing the light emitting unit towards the reflector.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention will be described by way of example, with reference to the accompanying drawings, wherein:
FIG. 1 is a plan view of a coordinate measuring machine;
FIG. 2 is a side view of the machine of FIG. 1;
FIG. 3 is a section on the line III--III in FIG. 2;
FIG. 4 shows a ram for use in the machine, viewed approximately on the line IV--IV in FIG. 1;
FIG. 5 is a schematic block diagram illustrating the control of the machine;
FIG. 6 is a side view of a modified coordinate measuring machine;
FIG. 7 shows the ram of FIG. 4, with a modified measuring arrangement;
FIG. 8 is a view on the line VIII--VIII in FIG. 6;
FIG. 9 is an isometric view of a component from FIGS. 7 and 8;
FIG. 10 shows a ram with an alternative measuring arrangement; and
FIG. 11 is a side view of another embodiment of coordinate measuring machine.
DESCRIPTION OF PREFERRED EMBODIMENTS
Most of the following description relates to coordinate measuring machines (CMMs), but the invention is also applic
REFERENCES:
patent: 4457625 (1984-07-01), Greenleaf et al.
patent: 4621926 (1986-11-01), Merry et al.
patent: 5387969 (1995-02-01), Marantette
Epps Georgia Y.
Kim Robert
Renishaw plc
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