Communications: electrical – Audible indication – Percussion-type sound producer
Patent
1984-04-20
1986-12-23
Hix, L. T.
Communications: electrical
Audible indication
Percussion-type sound producer
H03M 122
Patent
active
046315195
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with position measuring apparatus for providing a measure of the relative position of two members movable relative to one another in a predetermined path. Embodiments of the invention may be applicable to a wide range of instruments in which such relative position measurements must be made.
Digital transducers are known which enable displacement along a digitised track to be measured. Commonly, the track comprises of a regular series of digitiser elements, or bits, and the displacement along the track is measured by counting the number of bits. For such arrangements to measure the position along the track, a record must be kept of the count from a predetermined datum. This record can be lost in the event of power failure. Furthermore, some modification of the basic arrangement is required to accommodate two-directional movement along the track so that the counter can be incremented or decremented appropriately.
Alternative digital transducer arrangements employ absolute digital encoding of successive positions along the length of a track. Such a system has limitations in terms of the length of the track which can be covered given the size of digital word representative of each position along the track. Furthermore, only the predetermined coded positions can be recorded so that the accuracy of positional measurement is limited.
The possibility of measuring the present position of a moving member relative to a track is discussed by B. E. Jones and K. Zia in the paper entitled "Digital Displacement Transducer Using Pseudo-Random Binary Sequences and a Micro Processor" in IMEKO/IFAC, Symposium Proceedings, London, November 1980, pages 368 to 379. The system discussed by Jones and Zia enables relatively long digitiser tracks to be employed but necessarily involves movement of the moving member relative to the track in order for the position along the track to be identified. Furthermore, the system is capable of measuring the relative positions only to the accuracy of the digitiser bit spacing along the track. In a pseudo-random binary sequence (PRBS) having a total length of P bits, any group of a predetermined number r of consecutive bits, P being larger than r gives a unique pattern and hence defines the position of the group within the sequence.
U.K. Patent Specification No. 1511044 discloses a PRBS on a long perforated strip with means for reading the markings during relative movement of two members.
In U.K. No. 1284641, there is disclosed position measuring apparatus using markings in a PRBS on one member with means on a relatively movable member to scan mechanically the sequence of markings and hence to determine the relative position of the two members. Interpolation between successive coded increments is performed using a second ruled scale and a reference grating.
It is an object of the present invention to provide an improved position measuring apparatus which can determine the relative position of two members, which may be stationary during operation by scanning a PRBS but which can interpolate between the elements of the PRBS.
According to the present invention, position measuring apparatus for providing a measure of the relative position of two members movable relative to one another in a predetermined path comprises code elements on one of said members distributed among locations spaced parallel to said path of relative movement to define a predetermined sequential pattern of said locations in a pseudo-random binary sequence (PRBS) in which indexed positions corresponding to successive said spaced locations along the sequence are each identified by a unique binary word in a predetermined number of adjacent said locations, and detecting means, having sensing elements located on the other of said members, responsive to the code elements in at least said predetermined number of adjacent locations to read the unique binary work defined thereby to identify the corresponding indexed position along the sequence, said detecting means having a plurality of sensing element
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patent: 3702471 (1972-11-01), Kennedy et al.
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patent: 4071818 (1978-01-01), Krisst
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patent: 4112295 (1978-09-01), Dubik et al.
Jones, B. E. and K. Zia., Digital Displacement Transducer Using Pseudo-Random Binary Sequences and a Micro Processor, in IMEKO/IRAC, Symposium Proceedings, London, Nov. 1980, pp. 368 to 379.
Gray David M.
Hix L. T,.
Rosemount Engineering Company Limited
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