POSITION DETECTION APPARATUS

Abstract: An apparatus for position detection using signal patterns created by use of a fixed disk having three conductive patterns disposed thereon. The first and second patterns are annular conductive paths which are coaxial with respect to one another and the third pattern consists of radially extending conductive portions which are electrically connected to the second pattern. A brush carried by a rotating member whose position is sought to be determined is maintained in contact with the first and third pattern. In this manner an electrical signal variation is encountered as the radially extending conductive portions are encountered by the brush upon rotation thereof. This variation is thus correlated to the pattern defined on the third pattern. A microprocessor is used to add or subtract signals as the brush is rotated from a reference position based upon indicia of motor direction. Sequential radially extending conductive portions of said third pattern are arranged into subgroups which provide a unique signature corresponding to the respective position. A stored positional value is updated as rotation is initiated and after sufficient rotation has occurred to identify a subgroup, a comparison is performed to detect the presence of error. If no error is present the position will continue to be updated; adding and subtracting pulses. If an error is detected, the new subgroup and pulse position therein will be accepted as the correct positional value.

Description: POSITION DETECTION APPARATUS BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to position detecting apparatus and, more specifically, to position detecting apparatus using a unique pulse pattern to define and continuously verify a respective position detection. DESCRIPTION OF THE RELATED ART In many control applications it is necessary to know the position of a movable portion of the system. Several methods have been used to accomplish such an objective. A first group of methods provides an absolute position of the system at any given point. These sensors typically utilize a potentiometer which provides a resistance value corresponding to a specific position. The advantage of this type of system is that there is no loss of reference such that the system requires calibration. A second group of position sensors are relative in nature. These systems have a zero or calibration point and generate pulses as the system moves from this point of calibration. The system position is determined by adding or subtracting the pulses that are encountered or generated as the system moves from the zero position. Typically, these pulses are provided by use of a hall effect sensor, an optical sensor or a make-or-brake switch configuration. The advantage of such a system is its simplicity over the absolute sensors. The disadvantage is that if the pulses are counted in the wrong direction, the system will not correctly correspond to the position indicated . Another disadvantage is that if a stored position is incorrect, the system has no means of self calibration to provide continuous error correction. SUMMARY OF THE PRESENT INVENTION The present invention includes an apparatus for position detection using signal patterns created by use of a fixed disk having three conductive patterns disposed thereon. The first and second patterns are annular conductive paths which are coaxial with respect to one another and the third pattern consists of radially extending conductive portions which are electrically connected to the second pattern. A brush carried by a rotating member whose position is sought to be determined is maintained in contact with the first and third pattern. In this manner an electrical signal variation is encountered as the radially extending conductive portions are encountered by the brush upon rotation thereof. This variation is thus correlated to the pattern defined on the third pattern. A microprocessor is used to add or subtract signals as the brush is rotated from a reference position based upon indicia of motor direction. Sequential radially extending conductive portions of said third pattern are arranged into subgroups which provide a unique signature corresponding to the respective position. A stored positional value is updated as rotation is initiated and after sufficient rotation has occurred to identify a subgroup, a comparison is performed to detect the presence of error. If no error is present the position will continue to be updated; adding and subtracting pulses. If an error is detected, the new subgroup and pulse position therein will be accepted as the correct positional value. These and other aspects of the present invention will become more readily apparent by reference to the following detailed description of the embodiments as shown in the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of the sensor used to determine position of a rotary shaft; Figure 2 is a side view of the sensor used to determine position of a rotary shaft; Figure 3 is a pulse pattern produced upon rotation of the disk of Figure 1 ; and Figure 4 is a flow chart of the operational characteristics of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment of the present invention, as shown in Figure 1 and Figure 2, comprises a sensor 10 defined as a generally radially extending surface 1 1 fixed rigidly with respect to movable component; rotatable shaft 1 2. Surface 1 1 includes a first and second pattern 13, 14 defined thereon. First pattern 13 is an annular conductive portion of surface 1 1 . A second coaxial annular pattern 14 comprises a first portion 1 5 being annular and a second portion 1 6 comprising a pattern of radially extending conductive portions having a first void between sequential radially extending portions. The radially extending conductive portions are organized into sequentially unique subgroups which are separated by a second void. Each subgroup offering a sequentially unique signature is typically distinguished by an incremental radially extending portion. The groups are divided into subgroups and main groups as shown in Figure 3. The radially extending surface 1 1 is preferably constructed of an insulating material providing a high dielectric strength. The respective patterns are formed of a conductive coating which may be silk screened thereon or applied using known techniques of decalcomania or prepared and applied as metal stampings or prepared using known techniques of chemical etching. A first connection 20 known to those skilled in the art as a typical soldered connection provides electrical communication with first pattern 1 3 connecting same to a system ground. A second connection 22 connects annular portion 1 5 of the second pattern 14 to a 1 2 volt source through resistor R24. R24 provides a known circuit load. A low pass filter 1 1 1 is incorporated to eliminate any unwanted signal distortion due to brush contact discontinuity from bounce or dirt. Microprocessor 26 monitors voltage variation at point A of the respective circuit. A brush 28 is connected to rotary disk 30 by pin 32 and maintained in electrical continuity between portion 1 6 of pattern 14 and pattern 1 3. Brush 28 is a conventional sliding commutating brush which is well known to those skilled in the art. Such a system may be used to generate a signal pattern illustrated in Figure 3 which includes a reference or calibration position shown as locus 31 corresponding positionally with a first signal 34 spaced from a sequentially appearing pair of signals comprising subgroup 36, spaced from a sequentially appearing set of three signals comprising subgroup 37 spaced sequentially from a fourth set of signals comprising subgroup 38. The subgroups are positionally registered to correspond to unique positions of said movable component. Signal 34 and subgroup 36, 37, 38 collectively comprise a main group 1 1 2 which may be repeated about the perimeter of surface 1 1 or alternatively may appear as a singular main group comprising unique subgroups each featuring an incremental signal thereby providing a distinction from a sequentially preceding subgroup. Each sequential subgroup produces a unique signatured signal appearing as a respective group of voltage variations which provides a correlation to a specific location of rotary displacement. Such signal patterns are produced as a voltage variation as disk 30 carries brush 28 over the patterns defined on surface 1 1 . Using the signal pattern generated by the preferred embodiment of the present invention, it is possible to continuously verify the positional accuracy of a calculated position of a rotatable shaft by comparisons of calculated positions with actual positions. The calculated position can be determined by counting the signals or voids thereof encountered as the shaft is rotated from reference position 31 and adding or subtracting the signals or voids to a calibrated position. The decision to add or subtract is based upon a signal providing indicia of motor direction. Each sequential subgroup of pulses provides a unique signature consisting of the number of pulses present therein. If a calculated position does not match an actual position, the actual position is accepted. The system is initially calibrated by establishing a known position. Such a position may be an automobile window in closed position forced against a seal. Such a position is referred to as the calibrated position 410 of Figure 4. Movement from this position produces pulses which are counted and either added or subtracted in step 412. The decision to add or subtract is based upon motor direction. Once a subgroup has been identified in step 414, by comparison to stored signal sequence information, positional calculation determined in step 412 is compared in step 416 with the actual position of the respective identified subgroup. If the calculated and actual positions are identical, no error correction is made and the calculated position is verified. If not, position correction is made in step 420 accepting the actual position. The system is also capable of confirming direction of motion by the order in which the signal groups are generated. That is, if the signal groups are detected in a predetermined sequence, the direction is known from the sequence in which they appear. Finally, the velocity of the system can be determined by measuring the period of a signal as the signals are generated by the system. The preferred embodiment of the present invention incorporates a Motorola 68HC05P7 microcontroller. When programmed in machine language implementing the flow chart of Figure 4, the present invention provides an inexpensive and reliable sensor capable of monitoring the rotary position of a system component. One skilled in the art will readily recognize that certain specific details shown in the foregoing specification and drawings are exemplary in nature and subject to modification without departing from the teachings of the disclosure. Various modifications of the invention discussed in the foregoing description will become apparent to those skilled in the art. All such variations that basically rely on the teachings through which the invention has advanced the art are properly considered within the spirit and scope of the invention.

Claims: I Claim: 1 . An apparatus for detecting the position of a movable component of a system, said system having a fixed portion and a movable component, said movable component having a changeable position, said apparatus comprising: means for producing sequentially unique groups of signals disposed on said movable component; each said signal of said sequentially unique groups being dimensionally displaced from a sequential signal by a first void; said groups being dimensionally displaced from one another and separated by a second void; said groups being positionally registered to correspond to unique positions of said movable component; means to detect said signals disposed on said fixed portion; means for calculating a position of said system component changed from an initial position by counting signals detected as said movable component position changes with respect to said fixed component and adding or subtracting said signals based upon indicia of motor direction starting from a calibrated position to determine a calculated position; means for detecting errors in said calculated position by comparing said calculated position with an actual position detected by said means to detect said signals; and means for updating said calculated position to said actual position if said actual position and said calculated position are not identical. 2. The invention of claim 1 wherein said movable component comprises a rotary shaft drivingly engaged to a first radially extending member and said fixed portion comprises a second radially extending member. 3. The invention of claim 2 wherein said means for producing sequentially unique groups of signals disposed on said movable component comprises: spaced radially extending conductive portions arranged into sequentially unique groups; a circuit including a voltage source and a circuit load means; wherein said circuit is alternately completed as said spaced radially extending conductive portions contact a circuit portion disposed on said movable component. 4. The invention of claim 3 wherein said sequentially unique groups comprise a first group including one radially extending portion sequentially followed by a void which is sequentially followed by a second group including two spaced radially extending conductive portions. 5. The invention of claim 3 wherein said means to detect said signals disposed on said fixed portion comprises a microcontroller detecting variations in voltage in said circuit. 6. An apparatus for detecting the position of a system component having a position dependent upon a force means input through a shaft, comprising: a circular member, disposed coaxial to said shaft and fixed with respect thereto; a first annular portion disposed on said surface defining a continuous conductive path formed coaxial to said rotary shaft; a second annular portion disposed on said surface defining a conductive path coaxial to said first annular portion; a third annular portion disposed on said surface including circumferentially spaced radially extending conductive portions; said second and said third portions being disposed in conductive relation to one another; a first connecting member providing an electrically conductive connection to said first annular portion and connecting said first annular portion to ground potential; a second connecting member providing a conductive connection to said second annular member and connecting said second annular portion to a voltage potential; a third means for slidable conductive connection between said first annular portion and said third annular portion and drivingly connected to said shaft, each said radially extending portion of said third portion is sequentially disposed from one another and produces variations in said voltage potential as said sequentially disposed radially extending portions are encountered by said third means for slidable conductive connection; means to detect said variations in said voltage potential; each said radially extending portion is arranged into sequentially unique groups which correspond to a respective rotary position; means for determining an actual position by detecting variations in said voltage potential appearing in patterns corresponding to said sequentially unique groups which correspond to respective rotary positions; means for calculating a calculated position changed from an initial calibrated position by addition or subtraction of detected occurrences of variations in said voltage potential based upon indicia of motor direction; and means for detecting errors in said calculated position by comparing an actual position with said calculated position and updating said calculated position to said actual position if said actual and calculated positions are not identical. 7. The invention of claim 8 wherein said circular member is constructed from ceramic. 8. The invention of claim 8 wherein said first, second and third portions are metal stampings. 9. The invention of claim 8 wherein said first, second and third portion comprise a chemically etched conductive surface. 10. The invention of claim 8 wherein said third means for slidable conductive connection comprise brushes. 1 1 . The invention of claim 8 wherein said means for determining a rotary position of said shaft comprises a microprocessor. 12. The invention of claim 8 wherein said radially extending portions of said third portion are organized into groups, each sequential group having an incremental radially extending portion whereby each group produces a group of pulses differentiable from the preceding group. 13. The invention of claim 8 wherein said radially extending portions of said third portion comprise a first group including one radially extending portion sequentially followed by a second group including two radially extending portions. 14. The invention of claim 8 wherein said radially extending portions of said third portion comprise a first group including one radially extending portion sequentially followed by successive groups comprising radially extending portions wherein each successive group includes an additional radially extending portion.

Inventors: STREET THOMAS, STREET, THOMAS
Applicants: ROCKWELL INTERNATIONAL CORP, STREET THOMAS, ROCKWELL INTERNATIONAL CORPORATION
Application year: 1993
Main classification: G01D5
IPC codes: G01D5, H02K29, H02P6