Magnetic rotary sensor for detecting absolute position of rotating body

• US 4,774,464 A
• Filed: 01/20/1987
• Issued: 09/27/1988
• Est. Priority Date: 01/20/1986
• Status: Expired due to Fees

• Current Assignee: Hitachi Automotive Engineering Company Limited (Hitachi, Ltd.), Hitachi, Ltd.
• Original Assignee: Hitachi Automotive Engineering Incorporated (Hitachi, Ltd.), Hitachi, Ltd.
• Inventors: Kubota, Masanori, Hoshi, Yoshikazu
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US07/004,622
• Time in Patent Office: 616 Days
• Field of Search: 324/173, 324/174, 324/207, 324/208, 324/252, 235/449, 235/493, 123/617, 340/347 P
• US Class Current: 324/207.25
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01D 5/2455 with incremental and absolute tracks on the same encoder
• CPC Class Codes: H03M 1/143 in pattern-reading type converters, e.g. having both absolute and incremental tracks on one disc or strip H03M1/16 takes precedence
• CPC Class Codes: H03M 1/207 using a digital interpolation circuit
• CPC Class Codes: H03M 1/24 using relatively movable reader and disc or strip
• CPC Class Codes: H03M 1/303 Circuits or methods for processing the quadrature signals

Abstract

A magnetic rotary sensor has a rotary drum carrying thereon magnetically recorded codes representative of discrete positions obtained by dividing one rotation of the drum into a predetermined number of positions. Further, an interval between the adjacent discrete positions identified by the codes is interpolated by interpolation signals generated on the basis of a sine wave signal and a cosine wave signal, which are so produced by magnetic signals additionally recorded on the drum that the periods thereof correspond to the interval. Accordingly, a magnetic rotary sensor can be realized, which is capable of identifying the rotational positions of a rotating body with high resolution without increasing the rotary drum in size.

Claims

1. A magnetic rotary sensor for identifying absolute positions of rotation of a rotating body, comprising:

rotary means coupled with the rotating body for rotation therewith, the rotary means including a magnetic recording portion divided into plural tracks extending in the rotational direction of the rotary means, each of the plural tracks having magnetic signals recorded thereon by alternating arranging a magnetized portion of a predetermined length and a non-magnetized portion of the same predetermined length so that codes representing absolute positions are formed in a direction perpendicular to the rotational direction of the rotary means;

magnetic sensing means including plural magnetic sensing units disposed to face corresponding tracks of the rotary means for detecting the magnetic signals recorded on the respective tracks and for producing electric signals in accordance with the recorded magnetic signals as the rotary means rotates;

processing means for processing the electric signals from the magnetic identifying a particular one of primary positions represented by the codes and determined by dividing one rotation of the rotary means into a predetermined number of positions;

the rotary means further including two additional tracks on the magnetic recording portion thereof, the two additional tracks extending in the rotational direction of the rotary means and having magnetic signals consecutively recorded therealong, the signals recorded on one of said additional tracks being phase shifted a predetermined phase difference from the signals recorded on the other of said additional tracks;

the magnetic sensing means including additional sensing units for detecting the magnetic signals recorded on the two additional tracks and for providing two auxiliary signals having said predetermined phase difference from one another and having magnitudes which change sinusoidally in accordance with the rotation of the rotary means, a period of each of the auxiliary signals corresponding to an interval between two adjacent primary positions; and

the processing means being responsive to the two auxiliary signals for generating in accordance with the magnitudes of linearly changing portions in the two auxiliary signals an interpolation signal representing one of the rotational positions intervening between the two adjacent primary positions, and for combining the interpolation signal with a signal representing one of the two adjacent primary positions to produce the digital signal for identifying one of the absolute positions of the rotary means.

2. A magnetic rotary sensor according to claim 1, wherein the processing means includes means for discriminating in accordance with the magnitudes of the linearly changing portions in the two auxiliary signals one of four regions determined by dividing an interval between the two adjacent primary positions by four, and for generating the interpolation signal in response to the discriminated region.

3. A magnetic rotary sensor according to claim 2, wherein the processing means further includes means for calculating absolute values of differences of the two auxiliary signals with respect to a predetermined reference value, means for selecting a smaller one of the calculated absolute values, the discriminating means discriminating in accordance with the selected absolute value one of sections determined by dividing one of the regions by two, and generating the interpolation signal in response to the discriminated section.

4. A magnetic rotary sensor according to claim 2, wherein the processing means further includes means for calculating absolute values of differences of the two auxiliary signals with respect to a predetermined reference value, means for selecting a smaller one of the absolute values, and means responsive to the selected absolute value for retrieving position data from a table storing data of positions intervening between two adjacent primary positions with respect to the absolute values and for generating the interpolation signal in accordance therewith.

5. A magnetic rotary sensor for identifying absolute positions of rotation of a rotating body by a digital position signal of a predetermined number of bits, comprising:

rotary means coupled with the rotating body for rotation therewith, the rotary means including a first magnetic recording portion divided into a number of tracks equal to the predetermined number of bits of the digital signal, the tracks extending in the rotational direction of the rotary means and having magnetic signals recorded therealong by arranging alternately magnetized portions each consisting of unit magnets and having a length different in the respective tracks and non-magnetized portions each having the same length as the corresponding magnetized portions so that codes representing the absolute positions are formed in a direction perpendicular to the rotational direction of the rotary means, and a second magnetic recording portion divided into at least two additional tracks having magnetic signals consisting of unit magnets consecutively arranged therealong, the magnetic signals in the respective additional tracks being shifted by a distance from one another in the rotational direction of the rotary means, the shifted distance being determined by the number of additional tracks provided;

magnetic sensing means provided on a stationary member and including a first group of magnetic sensing units facing corresponding tracks of the first magnetic recording portion for detecting the magnetic signals recorded on the tracks of the first magnetic recording portion and for producing main electric signals in accordance therewith, and a second group of magnetic sensing units facing corresponding tracks of the second magnetic recording portion for detecting the magnetic signals recorded thereon and for producing at least two auxiliary electric signals in accordance therewith changing sinusoidally with a predetermined phase difference from one another corresponding to the shifted distance and with a period corresponding to a phase difference between a main electric signal for the least significant digit of the digital signal and a main electric signal for the second least significant digit of the digital signal; and

processing means for processing the main electric signals from the first group of the magnetic sensing units to produce a primary digital signal identifying one of primary positions determined by dividing one rotation of the rotary means into a predetermined number of positions, and for processing the auxiliary electric signals to generate in accordance with a relationship of the magnitude of linearly changing portions of the auxiliary signals an interpolation signal representing one of subdivided positions intervening between two adjacent primary positions, and for combining the interpolation signal with the primary digital signal for producing the digital position signal representing a present position of the rotary means.

6. A magnetic rotary sensor according to claim 5, wherein, in the first magnetic recording portion, a magnetic signal for a predetermined digit of the digital position signal is shifted with respect to a magnetic signal for a digit which is one digit less significant than the predetermined digit by a distance equal to half a length of the magnetic signal for the one-digit less significant in the rotational direction of the rotating means.

7. A magnetic rotary sensor according to claim 9, wherein, in the second magnetic recording portion, two additional tracks are provided, the magnetic signals on one of the two additional tracks being shifted from the magnetic signal on the other of the two additional tracks by a distance equal to a quarter of a length of the unit magnet in the rotational direction of the rotary means, whereby an auxiliary electric signal produced by a magnetic sensing unit of the second group of magnetic sensing units facing the one additional tracks is a sine wave and an auxiliary electric signal produced by a magnetic sensing unit of the second group of magnetic sensing units facing the other of the two additional tracks is a cosine wave.