Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2000-04-27
2001-10-16
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250
Reexamination Certificate
active
06304079
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an incremental rotary encoder which is suitable for surveying instruments such as total stations, theodlites, or the like.
2. Description of the Related Art
Surveying instruments such as total stations, theodlites, or the like, in recent years are provided with an incremental rotary encoder as an angle measuring device for measuring horizontal or vertical angles. This angle is calculated using the sum of a first angle value (counter value) and a second angle value (interpolation value). Two signals of sine and cosine waves (sin &thgr;, cos &thgr;) having a phase difference of 90 degrees therebetween which are output from the sensors of the incremental rotary encoder when it is in operation are each coded into a binary signal with reference to a corresponding reference voltage to obtain the aforementioned first and second angle values. The counter value is obtained by counting the points of variation in the signal level of each of the binary coded signals, while the interpolation value is obtained by dividing a section between two adjacent points of variation in the signal level of the binary coded signal.
The interpolation value is calculated in accordance with the variation of the oscillation from the constant reference voltage. Therefore, if the median voltage of each sine wave signal deviates from the reference voltage thereof, the interpolation value is not precisely calculated, thereby including error.
This error will be hereinafter discussed in detail with reference to FIG.
5
. In
FIG. 5
it is assumed that Lissajous circle of either the sine or cosine wave that rotates about the intersecting point of the x-axis and the y-axis (each shown by solid lines) of a reference voltage deviates from the intersecting point to rotate about the intersecting point of the x′-axis and the y′-axis (each shown by dotted lines) of a median voltage. In this state, a point “a” on the deviated Lissajous circle has no declination relative to the y′-axis of the median voltage but has a declination “&agr;” relative to the y-axis of the reference voltage. This declination “&agr;” causes an error in an interpolative calculation for calculating the interpolation value.
Since the interpolation value is obtained by dividing an angle corresponding to one count of the aforementioned counter value, the influence of the voltage difference on the error of the interpolation value becomes greater the lesser the number of pulses per revolution of the incremental rotary encoder (i.e., as the angle per one count is greater).
SUMMARY OF THE INVENTION
An object of the present invention is to provide an incremental rotary encoder which makes it possible to reduce error in the interpolation value by adjusting the aforementioned median voltage that is used to process the phase difference signals which are output from the incremental rotary encoder when the incremental rotary encoder is in operation.
To achieve the object mentioned above, according to an aspect of the present invention, an incremental rotary encoder is provided which outputs two sine wave signals having a phase difference of 90 degrees when the incremental rotary encoder is in operation, the incremental rotary encoder including a binary coding circuit which codes each of the two sine wave signals into a binary signal; a voltage detector which detects the voltage of one of the two sine wave signals at the moment of variation in a signal level of the binary signal of the other of the two sine wave signals; and a controller including a calculator which takes an even number of voltage values detected by the voltage detector to generate an average of the even number of voltage values for each of the two sine wave signals.
Preferably, the calculator calculates a median voltage of each of the two sine wave signals in accordance with the average of the even number of voltage values, and performs an interpolative calculation in accordance with the detected voltage and the median voltage to calculate an interpolation rotational angle for the incremental rotary encoder.
The incremental rotary encoder further includes a rotary portion, a sensor which outputs two sine wave signals having a phase difference of 180 degrees with respect to each respective said two sine wave signals having a phase difference of 90 degrees, and a differential amplifier which amplifies a difference between the two sine wave signals having the phase difference of 180 degrees.
According to an embodiment, the calculator performs the interpolative calculation using the following equations (1) and (2):
X=X−V
C(COS)
and
Y=Y−V
C(SIN)
. . . (1);
&thgr;=tan
−1
(y/x) . . . (2);
wherein “X” and “Y” designate the voltages of the two sine wave signals of the SIN and COS signals, respectively; “V
C
” designates the medium voltage; and “&thgr;” represents the interpolation rotational angle.
Preferably, the incremental rotary encoder further includes a non-volatile memory. The median voltages V
C(SIN)
and V
C(COS)
are stored in advance in the non-volatile memory the and the controller reads out the stored values of the median voltages V
C(SIN)
and V
C(COS)
from the non-volatile memory to perform the interpolative calculation.
According to another aspect of the present invention, an incremental rotary encoder, which outputs two sine wave signals having a phase difference of 90 degrees when the incremental rotary encoder is in operation, includes a binary coding circuit which codes each of the two sine wave signals into a binary signal, a voltage detector which detects the voltage of one of the two sine wave signals at the moment of variation in a signal level of the binary signal of the other of the two sine wave signals, a controller comprising a calculator which takes an even number of voltage values detected by the voltage detector to generate an average of the even number of voltage values for each of the two sine wave signals, and a closed-loop circuit which compares the average voltage with a predetermined target voltage to bring the average voltage close to the predetermined target voltage.
Preferably the incremental rotary encoder further includes a rotary portion, a sensor which outputs two sine wave signals having a phase difference of 180 degrees with respect to each respective one of the two sine wave signals having a phase difference of 90 degrees, and a differential amplifier which amplifies a difference between the two sine wave signals having a phase difference of 180 degrees. The closed-loop circuit adjusts an offset voltage of the differential amplifier so that the average voltage coincides with the predetermined target voltage.
Preferably, the incremental rotary encoder further includes a non-volatile memory. The adjusted offset voltage is stored in advance in the non-volatile memory when the power is OFF, and the controller reads out the stored offset voltage from the non-volatile memory to adjust the voltage values X and Y, detected by the voltage detector, when the power is ON.
Preferably, the incremental rotary encoder further includes a magnetic drum, and first and second magnetic sensors arranged so as to be opposite from each other with respect to the axis of the magnetic drum.
According to another aspect of the present invention, a surveying instrument is provided which includes a leveling board; a pedestal coupled to the leveling board to be rotatable about a vertical axis relative to the leveling board; a collimating telescope coupled to the pedestal to be rotatable about a horizontal axis relative to the pedestal; a horizontal-angle measuring device for measuring an angle of rotation of the pedestal relative to the leveling board; and a vertical-angle measuring device for measuring an angle of rotation of the collimating telescope relative to the pedestal. At least one of the horizontal-angle measuring device and the vertical-angle measuring device includes an incremental rotary encoder, and the incremental rotary encode
Kenjo Katsuhiko
Shirai Masami
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Patidar Jay
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