Data processing: measuring – calibrating – or testing – Measurement system – Orientation or position
Reexamination Certificate
2000-06-07
2003-06-10
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Orientation or position
C033S0010PT, C033S706000
Reexamination Certificate
active
06577984
ABSTRACT:
The present invention relates to a process and a device for digital measurement of the position of one of two elements in relative motion. It preferably applies to the measurement of absolute angular position round one revolution of elements in rotation one relative to the other.
The problem of the measurement of angles of rotation, permitting knowledge at any moment of the absolute angular displacement of one piece in rotation relative to another, has generated an abundance of literature proposing a large number of solutions. These solutions have often themselves been sub-divided into multiple alternatives.
Basically, known solutions employ on the one hand encoding of positions and on the other a means for reading the codes, expressing and transmitting the instantaneous angular position of a piece in motion relative to a determined origin. This reading means, generally consisting of sensors, sends signals to a central electronic unit capable of calculating or reading the angular displacement effected and sometimes of using the calculated values to perform more extensive processing.
Such a process may for example be applied to a disc including the said codes, rotated relative to the measurement means for reading the angular position at the instant t.
Among the solutions proposed in the prior art, it is possible to distinguish several families of solutions, classified according to the encoding method employed, or according to the reading method.
Thus traditionally the methods based on parallel encoding are distinguished from those based on sequential encoding of the serial type. The reading methods are differentiated depending on whether they are direct or indirect.
Substantially, encoding is said to be parallel when the whole of the code expressing a position may be read in a single operation, at one clock signal. On the other hand, sequential encoding involves serial reading of the said code, which obviously requires a plurality of clock cycles, or a plurality of successive readings.
Encoding is direct when the angle value is read immediately, without the need to perform other calculations. On the other hand, encoding is said to be indirect when the measurement indicates a calculation base to which must be added or from which must be subtracted a value to obtain the precise angle to be measured. In accordance with one possibility, the above-mentioned disc is divided into encoded sectors, constituting the base value to which must be added or from which must be subtracted a number of steps travelled.
In this configuration with an encoded disc, direct parallel encoding may lead to a radial encoding structure, each code arranged radially on the disc corresponding to an immediately readable angular position. For the measurement resolution to be correct, the encoding must for example be effected over eight bits, which involves a resolution slightly lower than 1.5°.
Peripheral direct parallel encoding is also possible, if the positions are encoded around the whole periphery of the disc. The spacing of the elements of the code around the said periphery then corresponds to that of the sensors.
In both cases, the number of sensors employed by the measurement device is high (eight or nine), which makes this a relatively expensive solution and also increases the number of connection conductors. These solutions are applied when it is required to know the precise angular position right from the start-up of the system, which direct reading permits.
On the other hand, indirect solutions present a so-called shadow zone at start-up: in effect it is necessary at least to have changed sector to communicate an exact position. The choice of solution therefore depends on the specification and, in particular, on the possibility or otherwise of creating a shadow zone at start-up. Indirect encoding may be parallel, and in this case employs a smaller number of sensors than before, for the sectors into which the disc is divided are obviously more limited in number than the discrete angular positions: encoding over five bits, consequently requiring five sensors, would for example theoretically allow division of the disc into thirty-two sectors.
Indirect and sequential angular measurement solutions have also been proposed by serial encoding of the sectors. For example, document EP-A-0 575 663 proposes encoding employing three sensors and tracks on a rotating disc., Two of the tracks carry equidistant marks, and these two tracks are offset by a quarter of a period in order to provide two signals in quadrature when they are read by two sensors. This very classical solution permits determination of the direction of rotation and the displacement in number of steps. The document in question employs a third sensor reading a third track. This track bears marks grouped in sixes, which, read serially, give a binary number which is the absolute number of the corresponding sector. These groups of six marks are separated by groups of four marks, which are always the same, so that the organ receiving the read signal of this track can establish passage from one sector to the next or to the previous one. This group of 4 marks, known as a separator, is represented in this case by the 4 bit word “0110”. The two first-mentioned signals are directed to a NOR gate which gives a direction signal (Up/Down) and a clock signal which serves to synchronise the reading of the third track and to interpret it.
The same principal is revealed in the American patent U.S. Pat. No. 4,736,187; here again two sensors read the marks and provide two signals in quadrature, which, by means of a NOR, synchronise the reading of the 3rd track. This third track gives the absolute angular position of the organ in motion by means of codes equidistributed around its circumference. Here, the different codes are distant from each other, and it is their physical distance which allows the interpretation system to differentiate them from each other. This physical distance is measured by counting the two signals in quadrature. In fact, it may be considered that the distance between two codes, void of any mark, is read by the corresponding sensor as a sequence of “1” (or of “0”, depending on the arbitrary convention selected), which sequence never appears among all of the codes of the sectors. This sequence is therefore a separator made of n “1” (or “0”) bits.
The present invention also uses indirect and sequential encoding. However the method of encoding the sectors is such that it permits more rapid detection of the separators and provides good protection against false readings of the codes.
One of the possible applications of the invention, the measurement of the angle of rotation of a vehicle steering column, permits the existence of a zone of uncertainty at start-up. It also imposes a resolution such that this solution appears particularly appropriate, as will be seen in detail below.
Firstly, the invention relates to a process for digital measurement of the absolute position of an element including binary encoding created by means of encoding units of the same area, in motion relative to an element provided with an organ for reading the said coding, the said coding defining differentiated sectors each including an identical separation zone, called a separator, and a zone identifying a single sector, called an identifier, the list of codes of the identifiers being contained in a memory zone accessible via an organ for processing binary data transmitted sequentially bit by bit by the said reading organ when the elements are in relative motion.
This process is essentially characterised by the fact that the separator coding comprises a binary sequence which is excluded from the coding of the identifiers, consequently immediately identifying a separator, knowledge of the whole of the code of which permits deduction of the identifier which follows it and then the position of the sector which corresponds to it by scanning the memory zone containing the list of identifier codes.
Then knowledge of the absolute position of the sector of the element having the b
Clairet Patrick L.
Corbier Jean-Paul
Couronne Christine
Zeraffa Philippe
Barbee Manuel L.
Delphi Technologies Inc.
Hoff Marc S.
Twomey Thomas N.
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