Boots – shoes – and leggings
Patent
1991-01-09
1993-05-04
Cosimano, Edward R.
Boots, shoes, and leggings
33706, 33707, 33763, 377 18, G01B 310, G06F 1520
Patent
active
052087670
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to displacement measuring apparatus and particularly, though not exclusively, to a tape rule.
BACKGROUND TO THE INVENTION
It is known, e.g., from Patent Specification Nos. U.S. Pat. No. 4,162,781; GB-A-2056660 and GB-A-1571245 to read optical markings on a tape rule and derive therefrom information about the position of the tape. If only movement and direction are required to be known, then only two photosensors are required. A workable tape system can be made using this approach and an implementation of it is described in U.S. Pat. No. -4,161,781. In essence, such an arrangement counts output state transitions as the tape moves from a known position to an unknown position whose displacement is to be measured. But positional accuracy relies on accurate and reliable knowledge of the first position and on accurate transition counting. Should any error occur in counting during a movement, as a result of damage to the line of marks being counted, then subsequently the known position will be in error, and the tape as a whole will be useless.
A method and apparatus for determining the absolute position of a movable element mounted for movement along a path is described in U.S. Pat. No. 4,009,377 (Elms) and is based on the development of a pseudo-randum sequence of indicia that uniquely define the position of the movable element on the path. But the provision of a separate timing track is essential and errors in reading the timing track would result in spurious detected indicia and large errors in measured position from which recovery would be difficult. The use of binary sequences to address sections of a rotating device is described by B. Arazi, Electronics Letters, 20, 61-62 (19 Jan. 1984).
SUMMARY OF THE INVENTION
It is an object of the invention to provide a tape rule or other displacement measuring device in which an accurate measurement of current tape position can be deduced irrespective of whether or not the first position of the tape was known, and that is robust to erasure or failure to measure accurately some of the tape markings between the initial and the current tape positions. It is a further object of the invention to provide a displacement measuring device having a multiplicity of sensors responsive to different areas of a spatial code track of the tape, wherein an absolute tape position can be deduced from the code by analysis of a sequence of sensor output states brought about by tape movement.
Broadly stated the invention provides displacement measuring apparatus comprising a member having marks and spaces occurring along a position track and defining encoded opsitions, sensing means past which the member moves arranged to read marks and spaces from the position track, and decoding logic fed with the output of the sensing means and arranged to derive a tape position from sensed and decoded information from the position track. The use in a tape rule of a position track carrying encoded information that is not simply counted is believed to be new.
The invention therefore provides displacement measuring apparatus comprising reading means and a member that are relatively movable, wherein the member carries a position track defined by a sequence of alternative markings made in succession along the tape, wherein;
(a) the alternative markings record different values in a pseudo-random sequence which is the result of repetitive operations on a seed consisting of a small number of elements, the sequence having the property that a group of successive markings of length at least equal to that of the seed occurs at a single position in the sequence so that a succession of markings read from the track and of length at least equal to the seed defines an absolute position of the reading means and the member; and
(b) the reading means has at least three sensors arranged to respond to different locations within each marking with the pattern of the markings and the location of the sensors arranged so that only a single sensor changes state each time that the
REFERENCES:
patent: 4009377 (1977-02-01), Elms
patent: 4161781 (1979-07-01), Hildebrandt et al.
patent: 4195348 (1980-03-01), Kakutani
patent: 4631519 (1986-12-01), Johnston
patent: 4799798 (1989-01-01), Erb
F. Jessie MacWilliams et al, Proceedings of the IEEE, vol. 64, No. 12, Dec. 1976, pp. 1715-1729.
George-Kelso Simon
Lindop Jim
Ryan Paul T.
Sajip Vinay
Cosimano Edward R.
The Stanley Works
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