Geometrical instruments – Miscellaneous – Light direction
Reexamination Certificate
1999-05-27
2001-01-09
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Miscellaneous
Light direction
Reexamination Certificate
active
06170162
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a new, improved and precise rotary displacement measuring system in which both absolute and relative measurements of rotary position may be made, with compensation for run out (mechanical wobble or misalignment).
In the operation of various mechanical and electromechanical systems, it is necessary to monitor the position and displacement of either some element of the system or some object which is not part of the system. For example, in robotic systems it is almost always necessary to monitor and control the movement and position of various component parts of the systems, such as an arm, fingers or other grasping elements, etc. Such monitoring and control yields the dexterity and precision required for a robotic system to carry out its functions.
Two types of position and displacement measurement may be required in the above-described systems, these being linear displacement and position, and angular or rotary displacement and position. Prior art mechanisms for sensing rotary position and displacement most often utilized a direct connection between the article or object whose position or displacement is to be monitored, and some type of gauge, needle or other visual indicator. Of course, such mechanisms were typically large, cumbersome, unreliable, and lacked precision in carrying out the monitoring function.
A number of electrical and electronic devices have been proposed for measuring angular position and displacement including so-called rotary variable differential transformers, such as described in U.S. Pat. No. 4,910,488. These devices provide for measuring angular displacement by converting mechanical rotation into an analog electrical signal, which may then be connected to a digital output by a conventional A/D converter. In U.S. Pat. No. 4,851,835, a so-called rotary transmitter is disclosed in which rotation of a rotor relative to a pair of stators is determined by variation in capacitance between the rotor and at least one of the stators as the rotor turns. Some prior art rotary measuring devices use several detectors to detect capacitance between the detectors and an emitter but then the outputs from the detectors are integrated to produce a single output signal which is typically analog. As noted above, this analog signal may then be converted to a digital signal for use and interpretation by the user. Finally, prior art devices have typically utilized multiple inputs to excite an emitter and in particular certain sections or segments on the emitter causing it to emit different strength electric fields (usually different phases of an AC excitation signal). Detection of the rotary position of the emitter (or detector) relative to the detector (or emitter) is then made by detecting the variation in strength or phase of the emitted fields.
The above-mentioned electrical and electronic measuring devices, although reducing the bulkiness and imprecision problems of the prior art mechanisms, such devices still do not allow for the precision oftentimes desired in the mechanical and electromechanical systems in use or contemplated for use at the present time.
Other types of rotary displacement and position measuring transducers include resistance-based voltage dividers and optical encoders, both of which also suffer from one or more of the disadvantages mentioned above. For example, while optical encoders have made improvements in the precision of measurements, the devices are still relatively bulky because increased precision is obtained through increasing the number of sensors or other methods which require increased detector surface area.
A further drawback is that the rotary displacement and position measuring transducers above typically use a single type of encoder, either absolute or incremental. The precision of absolute encoders has been poor relative to incremental encoders, but incremental encoders require indexing to find a reference point for movement.
Therefore, it would be an improvement over the prior art to combine the precision of an incremental encoder with the benefits of an absolute encoder so as to provide a rotary displacement and position measuring transducer which is much smaller than the prior art, compensates for run out, and avoids the errors inherent in an analog based system by using geometric quantization to produce a desired digital output representing angular position.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a simple, reliable and precise apparatus and method for measuring angular position.
It is another object of the invention to provide such apparatus which is especially compact, contains few moving parts and requires few wires.
It is a further object of the invention to provide such apparatus which is simple to manufacture, lending itself to very large scale integration (VLSI) fabrication techniques.
It is also an object of the invention to provide such apparatus in which a plurality of discrete signals are developed to provide a precise indication of rotary position.
It is still another object of the invention to provide such apparatus requiring only a single input connection to excite a rotating emitter disk uniformly over its surface, with rotary position being determined by variation in location of an emitted electric field rather than variation in strength or phase of an electric field.
It is an additional object of the invention to provide such apparatus which compensates for misalignment of emitter disk elements and detector elements.
An additional object is to simultaneously produce absolute and high resolution incremental outputs.
The above and other objects of the invention are realized in a specific illustrative embodiment of a rotary displacement measuring system which includes a shaft whose rotary displacement is to be measured, mounted to rotate about its long axis, and an emitter disk coupled to the shaft to rotate as the shaft is rotated. In response to a single time varying voltage, the emitter disk develops electric fields at predetermined locations on the emitter disk, such locations varying circumferentially on the emitter disk. Also included is an array of detectors disposed in close proximity to the emitter disk, adjacent the path traversed when the emitter disk is rotated, to detect variation in locations of the electric fields as the emitter disk is rotated and to produce output signals representing variations in the electric field locations. In particular, a plurality of detectors detect variations in locations of electric fields on a plurality of tracks. Such variation provides an indication of the position and displacement of the emitter disk and thus of the shaft.
In accordance with one aspect of the invention, the emitter disk comprises a generally planar disk mounted on the shaft to rotate in the plane defined by the emitter disk and to direct electric fields normally from an active side of the emitter disk from different locations thereon. The detector comprises a generally planar plate disposed in a fixed position to be generally parallel with the emitter disk on the active side thereof to enable detection of variations in the location of electric fields as the emitter disk is rotated. The emitter disk is mechanically biased by a spring toward the detector plate, but out of contact therewith.
In accordance with another aspect of the invention, a plurality of concentric tracks are formed on the active side of the emitter disk, each track including a plurality of spaced-apart, but electrically connected, conductive sections. A conductive layer of material is disposed on the detector plate on the side facing the active side of the emitter disk for developing an electric field to capacitively couple the layer and the track sections when a voltage signal is supplied to the layer. The conductive sections are thus caused to develop time varying electric fields to be detected by the detectors. A voltage supply source supplies a voltage signal to the conductive layer of material on the detector plate.
REFERENCES:
patent: 3218635 (19
Jacobsen Stephen C.
Mladejovsky Michael G.
Bennett G. Bradley
Sarcos L.C.
Thorpe North & Western LLP
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