Geometrical instruments – Straight-line light ray type – Level
Reexamination Certificate
2000-04-27
2003-09-23
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Straight-line light ray type
Level
C033S0010PT, C033S290000, C341S011000, C341S015000
Reexamination Certificate
active
06622391
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an incremental rotary encoder which is suitable for surveying instrument such as total stations, theodlites or the like. The present invention also relates to a surveying instrument which incorporates a magnetic incremental rotary encoder.
2. Description of the Related Art
Some conventional surveying instruments such as total stations, theodlites or the like are provided with an incremental rotary encoder as an angle measuring device. For instance, an optical incremental rotary encoder is used to measure horizontal or vertical angles.
FIG. 10
shows a conventional optical incremental rotary encoder. This optical incremental rotary encoder is provided with a main scale
101
, a sub-scale
103
, an LED (light source)
105
, a collimating lens
107
and a photosenor (detector)
109
. The main scale
101
and the sub-scale
103
are positioned between the collimating lens
107
and the photosenor
109
. In this optical incremental rotary encoder, each of the two scales
101
and
103
is made of glass, which makes the weight of the encoder heavy. Furthermore, in this optical incremental rotary encoder, since the main scale
101
and the sub-scale
103
are arranged separately from each other in the axial direction (the vertical direction as viewed in
FIG. 10
) while the light source
105
and the collimating lens
107
, and the detector
109
need to be positioned on the opposite sides of the main scale and the sub-scale
101
and
103
, the space in which the optical incremental rotary encoder is disposed needs to be wide in the axial direction thereof.
Similar to the optical incremental rotary encoder, a magnetic incremental rotary encoder is also known as an angle measuring device. A magnetic incremental rotary encoder is generally provided, on an outer peripheral surface of a magnetic drum (graduator disc) thereof, with a multi-pole magnetized layer having a plurality of magnetized divisions equally divided by the number of divisions N (“N” being a positive integer). The magnetic incremental rotary encoder is further provided with a magnetic sensor positioned to face the multi-pole magnetized layer. This magnetic sensor is provided thereon with, e.g., four magnetoresistor elements which are disposed at equally spaced intervals whose pitch is smaller than that of the plurality of magnetized divisions of the multi-pole magnetized layer to detect the variation in the resistance values of the four magnetoresistor elements which vary in accordance with the rotation of the magnetic drum to thereby determine the rotational angle of the magnetic drum with high precision corresponding to the pitch of the plurality of magnetized divisions of the multi-pole magnetized layer. The angle of the pitch is determined according to an interpolative calculation.
The error of the surveying instrument due to eccentricity of the graduator disc (protractor disc) is restricted by the Japanese Industrial Standard. Therefore, in a surveying instrument of a high degree of precision, it is necessary to have two magnetic sensors which are positioned on the opposite sides (offset from each other by 180 degrees) of the graduator disc with respect to the axis thereof so as to compensate for error due to the eccentricity of the graduator disc by taking the average of the detected output voltages of the two magnetic sensors.
Surveying instruments are generally required to have a high degree of precision in their functions. However, in a magnetic incremental rotary encoder, the number of the magnetized divisions (the number of divisions N) of the multi-pole magnetized layer cannot be made as many as that of an optical incremental rotary encoder. Accordingly, influence of harmonic distortion within one pitch of the magnetized divisions is large due to dimensional error and/or deviation of the magnetic resistance curve from the ideal value thereof. Moreover, the magnetic incremental rotary encoder has to be made with extreme precision, so that it is necessary to use a large number of magnetic sensors or magnetoresistor elements to compensate for the harmonic distortion which occurs.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an incremental rotary encoder in which error due to eccentricity of the graduator disc thereof and also arbitrary-order harmonic distortion can be simultaneously compensated.
Another object of the present invention is to provide a magnetic incremental rotary encoder which can be incorporated in, and is suitable for, a surveying instrument. Another object of the present invention is to provide a surveying instrument incorporating a magnetic incremental rotary encoder.
Other objects will become apparent to one skilled in the art from a reading of the following disclosure and the appended claims.
To achieve the object mentioned above, according to an aspect of the present invention, an incremental rotary encoder is provided which includes a rotary portion, a first sensor and a second sensor, the first and second sensors being arranged so as to be opposite from each other with respect to the axis of the rotary portion. The second sensor is offset from the first sensor so that the phase of output voltage of the second sensor advances or delays with respect to the phase of output voltage of the first sensor by &pgr;/X, wherein “X” represents a real number of one or more than one.
In an embodiment, the second sensor is offset from the first sensor so that the phase of output voltage of the second sensor advances or delays with respect to the phase of output voltage of the first sensor by &lgr;/2n in the case where an n-order harmonic distortion is compensated for, wherein the pitch of the harmonic distortion is &lgr;
.
Preferably, third and fourth sensors are provided, independently of the first and second sensors, which are arranged so as to be opposite from each other with respect to the axis of the rotary portion. In this case, the fourth sensor is offset from the third sensor so that the phase of output voltage of the fourth sensor advances or delays with respect to the phase of output voltage of the third sensor by &lgr;/2m in the case where a m-order harmonic distortion is compensated for, wherein the pitch of the harmonic distortion is &lgr;/m.
Preferably, the second sensor is provided in the incremental rotary encoder so that a phase difference of the second sensor with respect to the first sensor is adjustable.
In an embodiment, rotary portion includes a magnetic drum which is rotatably supported by a stationary portion of an optical instrument in which the incremental rotary encoder is incorporated, wherein an outer peripheral surface of the magnetic drum includes a multi-pole magnetized layer having a plurality of magnetized divisions equally divided. Each of the first and second sensors includes a magnetic sensor which is fixed to the stationary portion to face the multi-pole magnetized layer. Each of the first and second sensors includes a plurality of magnetoresistor elements which are located at &lgr;/4 intervals on the each sensor, “&lgr;” representing the pitch of the plurality of magnetized divisions. Error due to eccentricity of the magnetic drum and the n-order harmonic distortion are compensated for at the same time by taking an average of detected outputs of the first and second magnetic sensors.
In an embodiment, the rotary portion includes a magnetic drum which is rotatably supported by a stationary portion of an optical instrument in which the incremental rotary encoder is incorporated, an outer peripheral surface of the magnetic drum including a multi-pole magnetized layer having a plurality of magnetized divisions equally divided. Each of the first, second, third and fourth sensors includes a magnetic sensor which is fixed to the stationary portion to face the multi-pole magnetized layer, wherein each of the first, second, third and fourth sensors includes a plurality of magnetoresistor elements which are located at &lgr;/4 or &lgr; (3/4) intervals on th
Kenjo Katsuhiko
Noguchi Masato
Shirai Masami
Greenblum & Bernstein P.L.C.
Gutierrez Diego
Pentax Corporation
Smith R. Alexander
LandOfFree
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