Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-11-26
2001-09-04
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S231150
Reexamination Certificate
active
06285024
ABSTRACT:
This invention relates to a combined torque and angular position sensor for use, for example, in an electrical power assisted steering system (EPAS).
WO95/06330 discloses a torque sensor in which there are two relatively movable rotary elements which each have alternating first and second regions of differing transmissivities, such regions acting to modulate optical radiation from a source to form an image on an optical sensor array. Data taken from the array is analysed by a data processor to determine the relative positions of the two rotary elements by detecting the widths of gaps between a first dark area created by a low transmissivity region on one rotary element and dark areas on opposite sides of the first dark area, such dark areas being created by two adjacent low transmissivity regions on the other rotary element.
In an EPAS system it is also necessary for the current absolute position of the rotary elements to be known and in WO95/06330 an arrangement is described in which a number of the low transmissivity regions on one rotary element is of width different from the remainder, so that an “index” position can be established when these regions are detected. It has been found that a single different low transmissivity region is sufficient for this purpose, but when the system is initially switched on the rotary elements may have to be turned through up to 180° to enable the index position to be detected.
It is an object of the present invention to provide a combined torque and angular position sensor in which the absolute position can be established without requiring any turning of the rotary elements at start-up.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention there is provided a combined torque and angular position detector comprising a source of optical radiation, an array of optical sensors, first and second elements interposed between the source and the array, said elements being rotatable together and also angularly movable relative to one another to a limited extent for torque measurement, said first and second elements each having a plurality of alternating first and second regions, the first regions having greater optical transmissivities than the second regions, said second element also having further regions of optical transmissivity intermediate the transmissivities of the first and second regions, said further regions each being of different angular width, and a data processor arranged to collect optical intensity data from each of the sensors of the array and operating to process such data to determine the angular position of the second element by measuring the width and position of an image of a detected one of said further regions thereon, and the relative angular displacement of the first and second elements by measuring the position of the image of a second region of the second element relative to the positions of the images of two adjacent second regions of the first element.
Preferably, the positions of the images first and second regions are determined by comparing the optical intensity data for each sensor of the array with an upper threshold value. Positions of the further regions are determined by comparing the intensity data for each sensor of the array with a lower threshold value.
Preferably, the further regions of the second element are arranged to lie centrally within the first regions thereof.
The second element may be formed by laminating a mask which defines the first and second regions with a transparent overlay which has semitransparent areas forming the further regions.
In accordance with a second aspect of the invention there is provided a combined torque and angular position sensor comprising a source of optical radiation, an array of optical sensors illuminated by said source, first and second elements interposed between the source and the array, said first and second elements being rotatable together and angularly movable relative to one another to a limited extent for torque measurement, each of said first and second elements having a plurality of alternating first and second regions, said first regions having greater optical transmissivities than the second regions, the second regions of second element varying in angular width such that the angular widths of the first regions thereof decrease progressively around said second element, and a data processor connected to receive optical intensity data from each of the sensors of the array and operating to process such data to determine the angular position of the second element by measuring the position and width of the image of the second regions of the second element, and the relative angular displacement between the elements by measuring the position of an image of a second regions of the first element relative to the positions of images of two adjacent second regions of the second element.
The second regions of the second element are preferably arranged with their centre lines equi-angularly spaced around the element.
There are preferably two sensor arrays at diametrically opposite positions. In this case the second regions of the second element are preferably arranged mainly in adjacent pairs around the second element, the two second regions of each pair being of the same angular width. To avoid having a situation where each array can “see” only second regions of the same width as each other, the pairs are staggered by the inclusion of single second regions at non-opposite positions.
In accordance with a third aspect of the invention, there is provided a combined torque and angular position sensor comprising a source of optical radiation, an array of optical sensors illuminated by said source, first and second elements interposed between the source and the array, said first and second elements being rotatable together and also angularly movable relative to one another to a limited extent for torque measurement, each of the first and second elements having a plurality of alternating first and second regions, the first regions being of greater optical transmissivity than the second regions, whereby a combined image of a zone of said elements is formed on the array, the widths of said second regions differing from one another such that in any position of the first and second element, images of second regions having a unique combination of angular widths are present in the image, and a data processor connected to receive optical intensity data from each of the sensors of the array and operating on such data to determine a coarse measurement of the angular position of the elements by identifying which unique combination occurs in the image, a fine measurement of angular position in accordance with the position of the image of a selected second region within the sensitive image and the relative angular position of the elements by determining the position of the image of a second region of one element relative to the images of two adjacent second region of the other element.
Preferably to obtain sufficient data to identify the unique combinations and measure the angular position and relative angular displacement with a high level of resolution and accuracy it is desirable to utilise two sources and two sensor arrays at diametrically opposite positions relative to the common axis of the first and second elements.
REFERENCES:
patent: 4678908 (1987-07-01), LaPlante
patent: 4866268 (1989-09-01), Tang et al.
patent: 5523561 (1996-06-01), Ironside et al.
patent: 5841132 (1998-11-01), Horton et al.
patent: 0 555 987 A2 (1993-08-01), None
Cesari and McKenna
Le Que T.
TRW Lucas Varity Electric Steering Ltd.
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