JP2741431B2 - Encoder that detects the movement position from any reference point - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoder for detecting a rotational position of a rotating shaft and a moving position of a moving body.

[0002]

2. Description of the Related Art A conventional encoder mounts a code plate optically or magnetically provided with a code on a rotating shaft or a moving body, and has a detection circuit for detecting a code on the code plate. A sine wave signal and a cosine wave signal having a phase difference of 90 degrees generated from the detection circuit by the movement of the body are shaped into a rectangular wave by a waveform shaper, and the rise and fall of the rectangular wave are counted by a counter. Thus, the position of the rotation axis or the moving body is detected in units obtained by dividing one cycle of the sine wave into four.

In addition, the sine wave sinθ and the cosine wave cos
When the value of θ is plotted on the vertical and horizontal axes and a Lissajous figure is drawn, a circle is drawn. Therefore, the rotation angle in one cycle of the sine wave can be determined from the values of the sine wave sin θ and cosine wave cos θ. Become. Therefore, a method of detecting a position based on an interpolation position signal of one cycle of a sine wave based on the values of the two sine waves is also known. In this case, a sine wave signal,
The cosine wave signal is shaped into a rectangular wave, and the rising and falling edges of the rectangular wave are counted by a counter, and the sine wave 1
When counting within a period divided into four, the lower 2
Assuming that the bit is NL and the other upper bits are NH, while the lower two bits change from 0 to 3, the sine wave 1
Within the cycle, the value of the upper bits other than the lower 2 bits indicates the number of sine waves. On the other hand, assuming that the interpolation value is M and the position where one cycle of the sine wave is divided into L is indicated by the value indicated by the value of the upper bits other than the lower 2 bits of the counter and the interpolation value M, A high-resolution position up to a position obtained by dividing one cycle of a sine wave into L can be detected. That is, the position P is obtained by the following first equation.

P = NH · L + M (1) On the other hand, when the value of the lower two bits of the counter becomes “0”, that is, when one cycle of the sine wave signal is counted,
The interpolation value M must also be "0". If the reference point position of the interpolation start is not the zero cross point of the sine wave, an accurate position cannot be detected. for that reason,
The reference position must be accurately adjusted to the zero cross point of the sine wave (the starting point of the sine wave).

[0005]

However, it is very difficult to accurately match the reference position with the zero-cross point of the sine wave. Due to the delay in the calculation of the interpolated interpolation value M and other reasons, the interpolation of the interpolated interpolation value M is difficult. In some cases, "0" does not match the lower two bits "0" of the counter. FIG. 5 and FIG. 6 are diagrams for explaining the relationship when this shift occurs. 5A shows a sine wave, FIG. 5B shows an interpolation value M, and FIG.
Indicates the value of the counter. When the lower two bits NL of the counter are "0" and the value N of the upper bits other than the lower two bits is N,
When H is n, the interpolated interpolation value M is originally 0 to (L / 4)
Must be a value of However, when the interpolation value M is close to the maximum value L of the interpolation value as shown in FIG. 5B, when the position is calculated by the above equation, P = n · L + M = about ( n + 1) L, and a value larger by about one cycle is detected as the position P.

As shown in FIG. 6, when the lower two bits NL of the counter are "3" and the value NH of the upper bits other than the lower two bits is (n-1), the value of the interpolation value M is calculated. Is close to "0" (if normal, M =
(3L / 4) to L) The position P
Is as follows, and is smaller by about one cycle.

P = (n−1) · L + M = approximately (n−1) · L Accordingly, the present applicant has developed an encoder that corrects the deviation between the reference point and the sine wave zero-crossing point, and has already disclosed in Japanese Patent Application No. Hei. 2-312650 (JP-A-4-184217)
As a patent application.

The present invention is a further improvement in that even if the sine wave zero-cross point and the reference point (the start point of interpolation) are shifted (shift of one unit of interpolation division), the position can be detected accurately. It is another object of the present invention to provide an encoder capable of detecting a position using an arbitrary point as a reference position.

[0009]

According to the present invention, there is provided a counter which outputs a sine wave and a cosine wave by moving a code plate, and counts (or doubles) a sine wave cycle four times (or twice) from the sine wave and the cosine wave. An interpolating means for interpolating one cycle of the sine wave from the sine wave and the cosine wave, and an encoder for detecting a moving position based on the count value of the counter and the interpolated value of the interpolating means. The storage means for storing the count value and the interpolation value of the counter at an arbitrary reference position, the count value and the interpolation value detected by the counter and the interpolation means, and the storage means. From the stored count value and the interpolation value, the difference between the sine wave starting point position of the current position and the reference position is rounded down to the decimal point, and the difference is multiplied by the number of interpolation divisions. Out of the reference position from the interpolation value By providing a means for calculating and outputting the moving position by adding the value obtained by subtracting the interpolated values, and so as to accurately detect the moving position from an arbitrary reference point.

[0010]

FIG. 1 is an explanatory view for explaining the principle operation of the present invention.
The value of the counter at the arbitrarily set reference position Ps (counter for counting the sine wave quadruple) is Ns, the interpolation value is Ms, the value of the counter detected as the current position Pr is Nr, and the interpolation value is Nr. Is the position of the start point of the sine wave Cs at the set reference position Ps (the start point of the interpolation at the zero crossing point), where
Is represented by the following two equations.

Pss = [(Ns / 4) × L−Ms] / L (2) Further, the position P of the start point of the sine wave Cr at the current position Pr
rs is represented by the following three equations.

Prs = [(Nr / 4) × L−Mr] / L (3) Then, the sine wave cycle number K between the current position Pr and the set reference position is calculated from the sine wave start position Prs of the current position Pr. The sine wave starting point position Pss of the setting reference position Ps is subtracted, and the decimal part is rounded off. The value of the sine wave cycle number K is expressed by the following four equations.

K = Prs−Pss = [(Nr−Ns) × (L / 4) −Mr + Ms] / L (4) (rounded off to the decimal point) By multiplying the number L and adding a value obtained by subtracting the interpolation value Ms at the set reference position from the interpolation value Mr detected as the current position, the current position Pr is obtained as in the following five equations. .

Pr = K × L + Mr−Ms (5) Next, the reason why the current position Pr obtained by the above equations 2 to 5 is accurately obtained will be described.

As shown in FIG. 2, when the set reference position Ps or the current position Pr is at the switching position of the counter (when the setting reference position Ps or the present position Pr is not at the switching position, the detection position error does not occur particularly,
Since the set reference position Ps and the current position Pr can take arbitrary positions, it is necessary to assume that these positions are at these switching positions. ), The value Ns of the counter at the reference position Ps can be “ns” or “ns + 1”.
Then, the interpolation value Ms at that time can take a value of “ms” or “ms + 1”. Further, the value of the counter at the current position Pr can also take the value of “nr” or “nr + 1”, and the interpolation value Mr can take the values of “mr” and “mr + 1”. As a result, values obtained by subtracting the counter value Ns and the interpolation value Ms at the set reference position from the current value Nr and the interpolation value Mr of the counter are as follows.

Ns−Nr = nr−ns = n (nr−ns = n) = nr−ns−1 = n−1 = nr + 1−ns = n + 1 = nr + 1−ns−1 = n Mr−Ms = mr -Ms = m (assuming mr-ms = m) = mr-ms-1 = m-1 = mr + 1-ms = m + 1 = mr + 1-ms-1 = m As described above, the value of (Ns-Nr) is n-1, n, n +
1, the value of (Mr-Ms) is m-1, m, m + 1
It can take three ways. Therefore, the maximum value Kmax of the value of K before rounding obtained by the above equation (4) is
It looks like an expression.

Kmax = [(n + 1) × (L / 4) − (m−1)] / L = (1 / L) [(n × L / 4) −m] + [(1/4) + ( 1 / L)] (6) The minimum value Kmin is given by the following equation (7).

Kmin = [(n−1) × (L / 4) − (m + 1)] / L = (1 / L) [(n × L / 4) −m] − [(1/4) + ( 1 / L)] (7) On the other hand, the zero-cross point of the sine wave matches the interior reference position, and an accurate value is output. NS = ns, Ms = ms,
Assuming that Nr = nr and Mr = mr, the value of the sine wave cycle number K from the set reference position Ps to the current position Pr is the value of the following equation (8).

K = Prs−Pss = [(nr−ns) × (L / 4) −mr + ms] / L = [n × (L / 4) −m] / L (8) K represented by the above equation (8) Is determined when the zero-cross point of the sine wave matches the interpolation reference position, and the current position Pr
It is an integer since it is the number of cycles between the start points of the sine wave up to. This means that the first term on the right side in Equations 6 and 7 is an integer from Equation 8, and that [(1/4) + (1 / L)] of Kmax and Kmin is a decimal part. . Since the value of the interpolation division number L is obtained by dividing the sine wave into four by the counter, the value of the interpolation division number L divides the sine wave into four or more divisions, so that L> 4. As a result, [(1/4) + (1 / L)] <0.5 for the above-mentioned minority part. That is, the value of K expressed by equation 8 is represented by K0 (integer)
Then, the possible range of K is as follows.

K0−0.5 <K <K0 + 0.5 This means that if the value of K is rounded off, it always becomes K0,
Even if the zero-cross point of the sine wave is shifted from the interpolation reference position,
By performing the calculation of the above four equations and rounding off, the exact number of sine wave cycles K0 can be obtained. As shown in Equation 5, the current position Pr is obtained by multiplying the accurate sine wave cycle number K0 by the interpolation division number L, and further calculating the interpolation value ms of the set reference position Ps from the interpolation value mr of the current position. The value obtained by adding the subtracted value is the interpolation value mr, ms
Since the error of the difference is "2" at the maximum in the unit of interpolation division, there is no large detection error.

Since the reference position Ps can be set arbitrarily, the reference position Ps is determined immediately after the operation starts, and the value of the counter and the value of the interpolation value at that time may be stored.

[0022]

FIG. 3 is a block diagram of a rotary encoder according to one embodiment of the present invention. In FIG. 3, reference numeral 1 denotes a code plate. The code plate 1 is fixed to a rotating shaft or the like, and the rotation of the rotating shaft causes the code plate 1 to rotate, thereby detecting a code disposed on the code plate 1. The circuit 2 outputs a sine wave (pseudo sine wave) sinθ and a cosine wave cosθ having a phase difference of 90 degrees, similarly to the conventional rotary encoder. This 2
The two sine waves and cosine waves are shaped into rectangular waves by the waveform shaping circuit 3, and the edges of the two rectangular waves, that is, the rising and falling edges, are counted by the counter 4. Then, the microcomputer (MPU) 1 via the input port 5
Input to 0.

On the other hand, the sine and cosine waves are sampled and held by the sample and hold circuits 6 and 7 by timing pulses output from the timing pulse generator 12, and the values of the sampled and held sine and cosine waves are analog. / Digital converter (A / D converter) 8,
At 9, it is converted into a digital value and input to the MPU 10.

The detection circuit 2, the waveform shaping circuit 3, and the counter 4 are backed up by a battery, and are turned off.
, The rotation of the code plate 1 can be detected. Therefore, even if the rotary shaft rotates while the power is off, the counter 4 detects the rotation position, and when the power is restored, the counter 4 accurately determines the value of the counter 4 and the interpolation position obtained from the A-phase and B-phase signals. Position can be detected.

In this embodiment, the MPU 10 constitutes means for calculating and outputting the movement position Pr from a set reference position Ps, which will be described later, and the values of the counters 4 and the A / D converters 8 and 9. CPU), an input circuit, an output circuit, and the like. A ROM 11 stores a program executed by the processor of the MPU 10, a table for determining an interpolation position within one cycle of the sine wave from the values of the sine wave and the cosine wave, and a temporary storage of various operation data. This is a memory configured by a RAM or the like.

When the rotation axis and the code plate 1 are rotated and a sine wave signal and a cosine wave signal are output from the detection circuit 2, the respective signals are shaped by a waveform shaping circuit 3 and converted into rectangular waves. The edge of the rectangular wave is counted by the counter 4. Therefore, the counter 4 counts four pulses in one cycle of the sine wave, and detects one cycle as a quadruple value.

On the other hand, the sample and hold circuits 6 and 7 sample and hold sine and cosine waves according to the timing pulse from the timing pulse generator 12, and the A / D converters 8 and 9 convert the hold values into digital values and output them. I do. The timing pulse is also input to the MPU 10, and when the sample pulse is input, the MPU 10 calculates and outputs the position Pr.

The sine wave signal and cosine wave have a phase difference of 90 degrees. Therefore, for example, when a Lissajous figure is drawn by taking the value of the sine wave on the horizontal axis and the value of the cosine wave on the vertical axis, a circle is formed, and the combination of the sine wave and cosine wave values represents the phase position in one cycle of the sine wave. Will be. Therefore, 360 degrees of one cycle of the sine wave are divided into L, and division positions are stored in the ROM of the memory 11 according to the combination of the values of each sine wave and cosine wave. Read from the memory 11 to obtain a position obtained by dividing one cycle into L,
That is, an interpolation value can be detected. Alternatively, the interpolation position within one cycle can be calculated from the values of the sine wave and the cosine wave by the Newton's method conventionally used.

Next, the operation of this embodiment will be described. First, when power is supplied to the encoder, a reference position Ps is set. The reference position Ps may be an arbitrary position. For example, a specific position of the rotary shaft to which the encoder is attached is input as a reference position. When the reference position is input, MPU1
0 is the value Ns of the counter 4 when it is input, and A / D
The interpolation interpolation position Ms obtained from the values of the sine and cosine waves output from the converter is stored in the memory 11, and these values Ns and Ms become the set reference positions Ps.

Next, the MPU 10 starts the processing shown in FIG. 4, and reads the value Nr of the counter 4 through the input port 5 every time a sample pulse generated from the sample pulse generator 12 is detected (step S1). At the same time, the values of the A / D converters 8 and 9 are read to calculate an interpolation value Mr (step S2). Next, the value N of the set reference position
s, Ms, the read counter value Nr, and the interpolated interpolation value Mr
And the interpolation division number L, the arithmetic operation of Equation 4 is performed, and the decimal part is rounded off to obtain a sine wave cycle number K. The calculated sine wave cycle number K, the interpolation values Ms and Mr, and the interpolation division number are calculated. The current position Pr is obtained by performing the calculation of equation (5) from L and output (step S3). Hereinafter, this process is performed every time a sample pulse is detected.

Next, an example will be described in which this embodiment shows that a large error does not occur. For example, assume that the number of interpolation divisions L is 100 and the value ns of the counter 4 at the set reference position Ps in FIG. 2 is “10”. The interpolation value ms corresponding to the counter value ns = 10 is 0 to 24.
However, there is a case where the interpolation value ms can be 1 to 25 due to the presence of an error. Then,
The value ns of the counter 4 is not known whether it is "10" or "11". That is, at the setting reference position as shown in FIG. 2, the combination of the counter value Ns and the interpolation value Ms is
The street is conceivable. (Ns, Ms) = (10, 24), (10, 25),
(11, 24), (11, 25) Similarly, when the current position Pr is also as shown in FIG. 2 and the value nr of the counter 4 is “16”, the value Ns of the counter is
And the interpolated interpolation value Ms are considered in the following four combinations. (Nr, Mr) = (16, 74), (16, 74),
(17, 75), (17, 75) Regardless of the combination of the counter values Ns and Nr and the interpolation values Ms and Mr, the value of the sine wave cycle number K calculated by the above equation (4) is always the same. There must be.
Otherwise, as shown in Equation 5, the current position Pr is a sine wave 1
It will be shifted by a cycle. Therefore, there are three types of Nr-Ns = 5, 6, 7 and three types of Mr-Ms = 49, 50, 51.

The combination that maximizes the value of K is Nr
−Ns = 7 and Mr−Ms = 49, K = (7 × 25−49) / 100 = 1 (rounds 1.26) The combination that minimizes the value of K is Nr−Ns = 5 At the time of Mr−Ms = 51, and K = (5 × 25−51) / 100 = 1 (round off 0.75), and the value of K is always constant. As a result, the current position Pr calculated by equation (5) is only an error caused by (Mr−Ms), and has no significant effect.

In the above embodiment, the timing pulse generator 12 is provided, but instead of the timing pulse generator 12, a signal is output from the MPU 10 at predetermined intervals (every processing interval shown in FIG. 4). The data is read from the input circuits 12 and 13 with this signal, sampled and held and with a slight delay thereafter.
May be performed.

Further, in the above embodiment, the detection circuit 2, the waveform shaping circuit 3, and the counter 4 are backed up by a battery.
After the power is turned on, a moving rotary shaft or a moving body for detecting a moving position is positioned at a specific position by an encoder, and the position is used as a reference position to set a counter value Ns and an interpolation value Ms.
May be stored.

[0035]

According to the present invention, an arbitrary reference position can be set as the reference position, and the position can be accurately detected even if the zero-cross point of the sine wave is shifted from the start point of the interpolation.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating the operation principle of the present invention.

FIG. 2 is an explanatory diagram of an error generation cause.

FIG. 3 is a block diagram of a rotary encoder according to one embodiment of the present invention.

FIG. 4 is a flowchart of a process performed by the microcomputer of the embodiment.

FIG. 5 is an explanatory diagram illustrating a difference between a counter value and an interpolation position.

FIG. 6 is an explanatory diagram for explaining another difference between a counter value and an interpolation position.

[Explanation of symbols]

 1 code board 2 detection circuit 3 waveform shaping circuit 4 counter 5 input port 6,7 sample hold circuit 8,9 analog / digital converter (A / D converter) 10 microcomputer (MPU) 11 memory 12 sample pulse generator Ps Setting reference position Pr current position

Claims (1)

(57) [Claims] 1. A counter for outputting a sine wave and a cosine wave by moving a code plate, counting the sine wave cycle from the sine wave and the cosine wave four times, and within one cycle of the sine wave from the sine wave and the cosine wave. In an encoder having interpolation means for interpolating the count value and detecting the moving position based on the count value of the counter and the interpolation value of the interpolation interpolation means, the count value of the counter at an arbitrary reference position and the interpolation value A storage means for storing a value, a count value and an interpolation value detected by the counter and the interpolation means, and a sine of a current position and a reference position based on the count value and the interpolation value stored in the storage means. The difference between the wave starting point positions is obtained by rounding off the decimal point or less, and a value obtained by subtracting the interpolation value at the reference position from the detected interpolation value to the value obtained by multiplying the difference by the number of interpolation divisions. Means to calculate and output the movement position by adding An encoder for detecting a movement position from an arbitrary reference point.