Magnetic encoder and survey instrument having magnetic encoder

• US 6,492,806 B2
• Filed: 06/13/2001
• Issued: 12/10/2002
• Est. Priority Date: 06/14/2000
• Status: Expired due to Fees

• Current Assignee: Pentax Corporation (Hoya Corporation)
• Original Assignee: Pentax Corporation (Hoya Corporation)
• Inventors: Shirai, Masami
• Primary Examiner(s): Lefkowitz, Edward
• Assistant Examiner(s): KINDER, DARRELL D
• Application Number:
  US09/879,162
• Publication Number:
  US 20020005716A1
• Time in Patent Office: 545 Days
• Field of Search: 324/207.21, 324/207.25, 324/207.12, 33/1.N, 33/1.PT, 332/81, 332/82, 332/85, 332/90, 332/91, 341/15
• US Class Current: 324/207.12
• CPC Class Codes: G01C 1/02 Theodolites
• 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 5/24438 Special design of the sensing element or scale
• CPC Class Codes: G01D 5/2451 Incremental encoders G01D5/2454 takes precedence

Abstract

A magnetic incremental encoder includes a plurality of detection devices which are provided on an outer periphery of a rotational member at a predetermined phase difference, wherein each of the detection devices outputs signals which vary periodically in accordance with the rotational angle of the rotational member upon rotation thereof; wherein the plurality of detection devices are provided in sets of two detection devices on the outer periphery of the rotational member, wherein a phase difference between one of the sets of two detection devices and an adjacent another of the sets of two detection devices is determined according to the following formula:

2πP+π/j;

wherein P designates an arbitrary integer; and j designates one of the number of k orders, wherein k designates the number of orders of harmonic distortions to be corrected. The number of the plurality of detection devices is equal to 2^k.

Claims

1. A magnetic incremental encoder comprising a plurality of detection devices which are provided on an outer periphery of a rotational member at a predetermined phase difference, wherein each of said detection devices outputs signals which vary periodically in accordance with the rotational angle of said rotational member upon rotation thereof;

wherein said plurality of detection devices are provided in sets of two detection devices on the outer periphery of said rotational member, wherein a phase difference between one of said sets of two detection devices and an adjacent another of said sets of two detection devices is determined according to the following formula;

2. The magnetic incremental encoder according to claim 1, further comprising a calculation device which calculates an arithmetic mean of the detection signals of said plurality of detection devices to obtain a detection angle whose harmonic distortions of k order have been corrected.

3. The magnetic incremental encoder according to claim 1, wherein in order to correct k number of different order harmonic distortions, the phase difference between one of said sets of two detection devices and an adjacent another of said sets of two detection devices is determined by said formula at a first order of j order of the number of k orders;

wherein said one of said sets of two detection devices and said adjacent another of said sets of two detection devices constitute a group of detection devices.

4. The magnetic incremental encoder according to claim 3, wherein the phase difference between one group of detection devices and an adjacent another group of detection devices of said plurality of detection devices is obtained by said formula at a j order other than said first order, of the number of k orders.

5. The magnetic incremental encoder according to claim 1, wherein in order to correct n^th order and m^th order harmonic distortions, two sets of detection devices are provided;

each set of detection devices comprising two detection devices, each detection device of said two sets of detection devices being arranged with a phase difference determined by one of the following formulae;

6. The magnetic incremental encoder according to claim 1, wherein said rotary member is rotatably supported by a stationary portion of a device on which the magnetic incremental encoder is mounted, and said rotary member being a magnetic drum which is provided on the outer peripheral surface thereof with a multipolar magnetization layer having split sections magnetized at an equal pitch of λ

;

said detection devices being provided with magnetic sensors mounted to the stationary portion and opposed to the multipolar magnetization layer of said magnetic drum.

7. The magnetic incremental encoder according to claim 6, wherein said magnetic sensors are each provided with eight magnetroresistor elements arranged with a phase difference of λ

/4 to detect the magnetic field which varies in accordance with the rotation of said magnetic drum; and

wherein a detection signal is produced in accordance with the rotation angle of said magnetic drum, based on the detection outputs of four magnetroresistor elements which are deviated by λ

/2 and the detection outputs of the remaining four magnetroresistor elements which are deviated by λ

/2.

8. The magnetic incremental encoder according to claim 6, wherein said calculation device calculates the arithmetic mean of the rotation angles detected by all said magnetic sensors to obtain a rotation angle of said magnetic drum.

9. The magnetic incremental encoder according to claim 1, wherein additional detection devices, which have the same arrangement and number as said plurality of detection devices, are provided diametrically and symmetrically opposed to said plurality of detection devices, with respect to the center of rotation of said rotational member.

10. A survey instrument having a magnetic incremental encoder comprising a plurality of detection devices which are provided on an outer periphery of a rotational member at a predetermined phase difference, wherein each of said detection devices outputs signals which vary periodically in accordance with the rotational angle of said rotational member upon rotation thereof;

wherein said plurality of detection devices are provided in sets of two detection devices on the outer periphery of said rotational member, wherein a phase difference between one of said sets of two detection devices and an adjacent another of said sets of two detection devices is determined according to the following formula;