Magnetic position detection device and magnetic position detection method

A magnetic position detection method used by a magnetic position detection device, the magnetic position detection device including:

• a magnetic scale constituted by a first magnetic scale on which N magnetic poles and S magnetic poles of a uniform length λ1 are arranged alternately in a movement direction, and a second magnetic scale which is provided parallel to the first magnetic scale, and on which N magnetic poles and S magnetic poles of a uniform length λ2 are arranged alternately in the movement direction;
• a magnetism sensing device that is disposed opposite the first magnetic scale and the second magnetic scale via respective air gaps, and that moves in the movement direction relative to the first magnetic scale and the second magnetic scale through magnetic fields formed respectively by the first magnetic scale and the second magnetic scale while maintaining the air gaps, and measures using magnetism sensing elements variation in the magnetic fields during the relative movement;
• and
• a position calculation device that calculates absolute positions of the magnetism sensing elements relative to the magnetic scale by analyzing output values of the magnetism sensing elements, output by the magnetism sensing device,
• wherein a total number of magnetic poles obtained by adding together respective numbers of the N magnetic poles and the S magnetic poles included on the first magnetic scale is k, and a total number of magnetic poles obtained by adding together respective numbers of the N magnetic poles and the S magnetic poles included on the second magnetic scale is k+2, a difference between the respective numbers of magnetic poles being 2,
• the magnetism sensing device includes:
• a first magnetism sensing element group constituted by one or more magnetism sensing elements for detecting variation in the magnetic field formed by the first magnetic scale;
• and
• a second magnetism sensing element group constituted by one or more magnetism sensing elements for detecting variation in the magnetic field formed by the second magnetic scale,
• the magnetism sensing device outputs measurement results indicating variation in the magnetic fields during the relative movement in parallel by the respective magnetism sensing elements constituting the first magnetism sensing element group and the second magnetism sensing element group,
• a ratio of a number n of magnetism sensing elements in the first magnetism sensing element group to a number m of magnetism sensing elements in the second magnetism sensing element group is equal to a ratio of an inverse of the number k of magnetic poles on the first magnetic scale to an inverse of the number k+2 of magnetic poles on the second magnetic scale, and
• the magnetism sensing elements are arranged by setting an arrangement interval between the magnetism sensing elements of the first magnetism sensing element group at P1 so that output waveforms of signals output respectively by the magnetism sensing elements of the first magnetism sensing element group deviate from each other successively by a phase P1=λ1/n obtained by dividing the length λ1 of one magnetic pole of the first magnetic scale equally by the number n of magnetism sensing elements, and setting an arrangement interval between the magnetism sensing elements of second magnetism sensing element group at P2 so that output waveforms of signals output respectively by the magnetism sensing elements of the second magnetism sensing element group deviate from each other successively by a phase P2=λ2/m obtained by dividing the length λ2 of one magnetic pole of the second magnetic scale equally by the number m of magnetism sensing elements, or, in a case where one of the number n of magnetism sensing elements in the first magnetism sensing element group and the number m of magnetism sensing elements in the second magnetism sensing element group is an even number and the other is an odd number, the magnetism sensing elements are arranged by halving the even number of magnetism sensing elements,
• the magnetic position detection method comprising following steps executed by the position calculation device:
• a Hi/Lo determination step for binarizing n+m output values output in parallel by the respective magnetism sensing elements of the magnetism sensing device by determining whether the output values are Hi or Lo, and outputting the binarized output values as n+m Hi/Lo outputs;
• a storage step for storing in a storage unit a data table on which a relationship between the information indicating the absolute positions of the magnetism sensing elements relative to the magnetic scale and patterns of the n+m Hi/Lo outputs is defined in advance;
• and
• a position calculation step for calculating, on the basis of the data table stored in the storage unit in the storage step, the absolute positions of the magnetism sensing elements relative to the magnetic scale that correspond to the n+m Hi/Lo outputs output in the Hi/Lo determination step.