JP3034744B2 - Absolute encoder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an absolute encoder for detecting an absolute rotational position used in a servomotor of a machine tool.

[0002]

2. Description of the Related Art Conventionally, an absolute encoder such as a resolver or an optical encoder has been employed as means for detecting an angular position of a servomotor used for a robot or a machine tool. Are occupying a large weight in the performance of the servomotor. In particular, since the rotational unevenness and position control of the motor, which have recently become a problem, are determined by the performance of the angular position detector, an angular position detector having high resolution has been demanded. In the development of a direct drive motor capable of performing high-precision control, an angular position detector having high resolution is indispensable. Further, such a motor has a drawback in that the size in the axial direction becomes longer and the size of the entire device becomes larger. In particular, since a servomotor is used for a joint part in a robot or the like, it has become a serious problem.

[0003] In view of the above, conventionally, a high-resolution angle position detector of the shaft double angle mx for detecting the angular position of the shaft double angle mx (m ≧ 2) and an absolute position detector for detecting the angular position of the shaft double angle 1x are conventionally known. Absolute encoder capable of high-resolution angular position detection by arranging an angular position detector with a shaft multiple of 1x for angular position detection on a concentric circle and shortening the axial dimension for miniaturization Are being developed.

An example of a conventional absolute encoder capable of detecting such an absolute rotational position will be described. FIG.
FIG. 7 is a side sectional view showing a conventional absolute encoder, FIG. 7 is a sectional view taken along the line CC ′ of FIG. 6, and FIG. 8 is a block diagram showing an example of an electric circuit of the absolute encoder of FIG. FIG. 9 is a specific example of the interpolation circuit 20 of FIG. 6, and FIG. 10 is a timing chart.

This absolute encoder has a configuration in which one rotor 46 is clamped by two stators 41 and 51 arranged concentrically. In FIG. 6, a stator 3 is fixed to a fixed object (not shown) and supports an input shaft 1 via a bearing 2. The input shaft 1 is directly connected to a servomotor shaft (not shown), and the rotor 46 is fixed to the input shaft 1 and rotates together with the servomotor shaft. In FIG. 7, the outer stator 41 has eight pole teeth 4 provided on the inner side thereof at equal intervals along the circumferential direction.
Has two. Further, an input winding 44 and an output winding 45 are wound around each of the pole teeth 42 as shown. on the other hand,
The rotor 46 has ten teeth 47 on the outer peripheral side, and the relationship between each pole of the outer stator 41 and the teeth 47 of the rotor 46 shifts by 1/4 pitch every time the pole shifts by one. It is configured as follows. An eccentric hollow portion 57 is provided inside the rotor 46, and the hollow stator 57 has four pole teeth 52 provided at equal intervals along the circumferential direction. 51 are provided. Each of the pole teeth 52 also has an input winding 54 and an output winding 5 as described above.
5 is wound as shown.

[0006] Outer stator 41, pole teeth 42, input winding 4
4. A resolver including the output winding 45 and the teeth 47 is referred to as an outer resolver 40, and a resolver including the inner stator 51 and the pole teeth 52, the input winding 54, the output winding 55, and the hollow portion 57 is referred to as an inner resolver 50. .

In the absolute encoder configured as described above, the angular position is detected as follows.

First, the outer resolver 40 performs high-resolution angular position detection.
There are 0 resolvers with a shaft double angle of 10x. The detection principle utilizes a change in magnetic resistance. When the rotor 46 rotates, the positional relationship between the poles 42 of the outer resolver and the teeth 47 changes, so that the magnetic resistance changes. Then, the magnetic flux passing through the output winding 45 changes due to the change in the magnetic resistance. Therefore, when the rotation angle of the axis of the servomotor is θ, the rotation angle can be detected by configuring the magnetic flux to be a sin function of θ.

That is, the input windings 44 of the outer stator 41 are connected in series so that the directions of the generated magnetic flux are alternately opposite. The output windings 45 are connected in series one by one so that the direction of the received magnetic flux is reversed. Then, two sets of output windings are formed in the output winding. Therefore, when an excitation voltage of Asinωt (A is a constant) is applied to both ends of the input winding, the pole 42 of the outer stator 41 and the rotor 46
Is shifted by 1/4 pitch at a time, and the following voltage Va is applied to each set of output windings.
m and Vbm.

Vam = K · Asinωt · cos10θ Vbm = K · Asinωt · sin10θ where K is a constant.

Next, the inner stator 51 is for detecting the absolute angular position of the rotor 46, and has a shaft multiplication angle of 1x.
As a detection principle, a change in magnetic resistance is used as described above. In this case, unlike the above, the change in magnetic resistance is not performed by teeth, but the inner peripheral surface of the rotor 46 is decentered. This changes the magnetic resistance.

That is, the pole teeth 52 of the inner resolver are 90
Since the positions are shifted by degrees, winding connection is performed in the same manner as the outer resolver described above, and the input winding is connected to Asinωt.
, The output voltages Va and Vb similar to the field sum of the outer resolver are obtained in the output winding.

Va = L · Asinωt · cosθ Vb = L · Asinωt · sinθ where L is a constant.

The voltages Vam and V obtained as described above
bm, Va and Vb are obtained by the electric circuit shown in FIG.
High-resolution absolute angular position θ that represents one rotation as an absolute position
Is converted to

The electric circuit shown in FIG. 8 will be described. The absolute encoder has a timing generator 11 for generating a timing signal CLK.
Includes an excitation signal Asin based on the timing signal CLK.
An excitation signal generator 12 for generating ωt is connected,
An outer resolver 40 and an inner resolver 50 are connected to the excitation signal generator 12. And the outer resolver 4
0 and the timing generator 11 are connected to an interpolation circuit 20 for calculating the electrical angle θm, and the inner resolver 50 and the timing generator 11 are connected to the interpolation circuit 20 for calculating the electrical angle θa. I have. Further, the interpolation circuit 20 is connected to a third arithmetic circuit 15 for calculating the angular position θm ′, and the interpolation circuit 20 detects at least one-tenth rotation of the mechanical angle in units of 36 degrees. The fourth arithmetic circuit 17 for calculating the upper digit v to be calculated is connected. An adder 18 that calculates the absolute angular position θ by adding the angular position θm ′ and the upper digit v is connected to the third arithmetic circuit 15 and the fourth arithmetic circuit 17. The excitation signal generator 12 generates an excitation signal of Asinωt synchronized with the signal CLK of the timing generator 11 and sends it to the outer resolver 40 and the inner resolver 50. Each resolver has the voltage Va as described above.
m, Vbm and voltages Va, Vb. The voltage Vam,
The electrical angle θm (0 ≦ θm <360 degrees) representing one-tenth of the mechanical angle of 360 degrees as shown in FIG. 11 and the electrical angle representing the mechanical angle of 360 degrees by the interpolation circuit 20 are used for Vbm and the voltages Va and Vb. θa (0 ≦ θa <360 degrees) is calculated.

Here, the interpolation circuit 20 will be described with reference to FIGS. The interpolation circuit 20 has an amplifier 21 for amplifying the voltage Vam of the outer resolver 40 and an amplifier 22 for amplifying the voltage Vbm of the outer resolver 40. The amplifier 21 is connected to a sample-and-hold circuit 23. An A / D converter 25 for digitally converting the output is connected to the sample-and-hold circuit 23. The amplifier 22 is connected to a sample-and-hold circuit 24, and the sample-and-hold circuit 24 is connected to an A / D converter 26 for digitally converting the output. And A
The / D converters 25 and 26 are connected to a fifth arithmetic circuit 27 that calculates the electrical angle θm from the outputs of the A / D converters 25 and 26. Voltage Vam, Vbm of outer resolver 40
Is amplified by amplifiers 21 and 22 and input to sample-and-hold circuits 23 and 24. The sample-and-hold circuits 23 and 24 generate the excitation signal Asinω
The input signal is held when the hold signal HD synchronized with t is at “H” level, and is sampled when it is at “L” level. The A / D converters 25 and 26 output the sample-and-hold circuits 23 and 2 at the rise of the hold signal.
4 is converted into digital signals A and B. The fifth arithmetic circuit 27 calculates and outputs the electrical angle θm by taking the arc tangent of the result of dividing the digital signals A and B. The electrical angles θa of the voltages Va and Vb of the inner resolver 50 can be detected in the same manner as in the case of the outer resolver 40.

Then, the angle position θm and the angle position θa are determined by the fourth arithmetic circuit 17 based on the following equation to be 1 mechanical angle.
The upper digit v for detecting one-tenth rotation or more in units of 36 degrees is calculated.

V = INT (θa · 10/360 + 0.5
-Θm / 360). When 360 / 10v ≧ 360, v
= V-360 The third arithmetic circuit 15 calculates a high-resolution angular position θm ′ within one-tenth rotation of the mechanical angle based on the following equation.

.Theta.m '=. Theta.m / 10 Then, by adding the high-resolution angular position .theta.m' to the upper digit v, the high-resolution absolute angular position .theta. Representing one rotation as an absolute position can be detected.

[0020]

In the absolute encoder having such a structure, the axial dimension can be shortened, but the inner resolver having the shaft double angle of 1x has a structure in which the inner peripheral surface of the rotor 46 is eccentric. There were the following two problems.

The first problem is that if the rotation center of the rotor 46 is displaced from the center of the inner stator 51, a large position detection error occurs, and the target position detection accuracy cannot be obtained. An error occurs in the absolute angular position θ. The second problem is that the center of rotation of the rotor 46 and the center of rotation are displaced and the structure is not well balanced, so that vibration occurs when the rotor 46 rotates at high speed. In particular, the first problem is that if the number of double axes of the outer resolver is increased for higher resolution, the required position detection accuracy of the inner resolver becomes stricter, making it difficult to realize a high-resolution and small-sized absolute encoder. In addition, when the 1X resolver is disposed outside in order to increase the rotor diameter and reduce the influence of misalignment, the rotor diameter of the resolver with a shaft double angle of 10x for high resolution is reduced, and the highly accurate angular position is increased. It cannot be detected. Further, if the diameters of both resolvers are increased in order to reduce the influence of misalignment, there is a problem in that the resolver goes against miniaturization.

The manner in which an error occurs in the absolute angular position θ will be described with reference to FIG.

When the center of rotation of the rotor 46 is deviated from the center of the inner stator 51 due to processing, assembling, or external force, it is assumed that the rotor 46 is rotating at a constant speed. Then, the position detection error θa is given to the inner resolver.
e occurs, and the error becomes a sine wave of one cycle as shown in FIG. Since there is an error in the electrical angle θa of the inner resolver, the electrical angle θa has a substantially swelling linear shape as shown in FIG. On the other hand, the electrical angle θm of the outer resolver is shown in FIG.
1 (c). And these values are the third,
An absolute angle position θ calculated by the four arithmetic circuits and representing one rotation as an absolute position is obtained as shown in FIG. In FIG. 11 (d), although it is originally required to be linear, a stepwise error occurs because the error of the inner resolver is larger than ± 18 degrees. An absolute encoder having such an error cannot be used as an absolute rotational position detector used for a servomotor or the like of a machine tool.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide no error in the absolute angular position θ and no vibration even when the rotor rotates at high speed. Another object of the present invention is to provide a high-resolution and small-sized absolute encoder.

[0025]

SUMMARY OF THE INVENTION The present invention provides an absolute encoder for detecting an angular position within one rotation absolutely, wherein a mechanical structure and a magnetic structure are changed every 1 / p rotation (p is a natural number of 2 or more). The same stator and rotor are provided, and the shaft double angle is nx (n is a natural number of 2 or more)
And a stator and a rotor having the same mechanical structure and magnetic structure every 1 / q rotation (q is a natural number of 2 or more), and share an input shaft with the first resolver. Are arranged on the same plane and concentric circles, and the axis double angle is mx (m is 2
(The above natural numbers) and n and m are provided with a second resolver having a prime relationship with each other, and the one having a larger axis double angle is disposed outside.

[0026]

In the present invention, the mechanical structure and the magnetic structure of the stator and the rotor of the first resolver and the second resolver are the same every 1 / p and 1 / q rotations. Even if the rotation center of the rotor is displaced from the center of the stator, almost no position detection error occurs due to the structural cancellation effect, and no error occurs in the absolute angular position. Also, the mechanical structure of the rotor of the first resolver and the rotor of the second resolver is 1 /
Since it is the same for every p, 1 / q rotation, its center of gravity and the center of rotation are the same, and no vibration is generated even if the rotor rotates at high speed.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 1, 2, and 3 are views showing an embodiment of an absolute encoder according to the present invention. The same elements as those in FIGS. 6, 7, and 8 are denoted by the same reference numerals and description thereof is omitted.

The absolute encoder of the present invention is an improvement of the inner resolver of the prior art absolute encoder, and the configuration and operation of the outer resolver are the same as those of the prior art absolute encoder. In FIG. 1, the rotor 36 is fixed to the input shaft 1 and rotates together with the axis of the servomotor. In FIG. 2, the rotor 3
6, three vertices 60, 61, 62 equidistant from each other
A distorted circular hollow portion 37 having
The inner stator 3 having twelve pole teeth 301 to 312 provided at equal intervals along the circumferential direction in the hollow portion 37.
1 is provided. An input winding 34 and an output winding 35 are wound around the pole teeth 301 to 312 as shown. In FIG. 3, reference numeral 13 denotes a first arithmetic circuit that calculates an integer x based on the outputs θn and θm of the interpolation circuit 20, and 14 denotes an integer y based on the output θm of the interpolation circuit 20.
Is a second arithmetic circuit that calculates The first arithmetic circuit 13 and the second arithmetic circuit 14 assign integers x and y to the mechanical angle of 1
A ROM 16 for converting a higher-order digit z that detects one-tenth rotation or more in units of 36 degrees is connected.
An adder 19 for calculating the angular position θ ′ by adding the upper digit z and the output θm ′ of the third arithmetic circuit 15 is connected. The ROM 16 stores data as shown in FIG.

In the absolute encoder configured as described above, the angular position is detected as follows.

An inner side comprising a distorted circular hollow portion 37 having three vertices 60, 61, and 62 equidistant from the inner stator 31, pole teeth 301 to 312, an input winding 34, and an output winding 35. The resolver has an axial double angle of 3x. The detection principle utilizes a change in magnetic resistance, and three vertices 60, 61, and 6 that are equidistant from the inner peripheral surface of the rotor 36.
The magnetic resistance is changed by forming a distorted circle having two.

Here, an example of the shape of the hollow portion 37 will be introduced. The mechanical angle is θ, the reference radius is r, and the change in radius is d.
Assuming that r, the radius R of the hollow portion 37 is represented by the following function.

R = r−dr · cos 3θ The input winding 34 and the output winding 35 of the inner stator 31 are connected in the same manner as in the prior art absolute encoder.
That is, the excitation windings connected in series so that the directions of the magnetic fluxes generating the input windings of the pole teeth 301 to 312 are alternately opposite to each other, and the pole teeth 301, 303, 305, 307, 30
An A-phase output winding connected in series so that the directions of magnetic fluxes receiving the output windings 9 and 311 are alternately opposite to each other;
B-phase output windings are connected in series such that the directions of magnetic fluxes receiving the output windings of 02, 304, 306, 308, 310, and 312 are alternately opposite. Thus, when an excitation voltage of Asinωt is applied to both ends of the excitation winding, the pole teeth 32 of the inner stator 31 are shifted by 30 degrees, and the same shape as before rotation when the rotor 36 rotates 120 degrees. As a result, the following voltages Van and Vbn are generated in each set of output windings.

Van = J · Asinωt · cos3θ Vbn = J · Asinωt · sin3θ where J is a constant.

In the case of the inner resolver 30, since the mechanical structure and the magnetic structure of the rotor 36 and the inner stator 31 are the same every １ ／ rotation, the rotation center of the rotor is shifted from the center of the stator. However, the position detection error hardly occurs due to the structural cancellation effect. Further, since the mechanical structure of the rotor 36 is the same every ３ rotation, there is no vibration associated with the high-speed rotation of the rotor such as the conventional inner resolver.

The voltages Vam, V obtained as described above
bm, Van, and Vbn are converted into a highly accurate absolute angular position θ ′ that represents one rotation by an absolute position by the electric circuit shown in FIG.

The operation of the electric circuit shown in FIG. 3 will be described.
Inner resolver 30 to which the excitation signal of Asinωt is input
And the outer resolver 40 has the voltage V
am, Vbm and voltages Van, Vbn. Voltage V
am and Vbm and the voltages Van and Vbn are each reduced to 1/10 of the mechanical angle of 360 degrees as shown in FIG.
And an electrical angle θn (0 ≦ θn <360 degrees) representing one third of the mechanical angle of 360 degrees are calculated.

The first arithmetic circuit 13 calculates an integer x based on the following equation.

X = INT (θn · 10/360 + 0.5
− (Θm · 3 / 360-INT (θm · 3/36
0))) When x ≧ 10, x = x−10 and the second arithmetic circuit 14 calculates an integer y based on the following equation.
Is calculated.

Y = INT (θm · 3/360) The ROM 16 stores the integers x and y in the upper digit z for detecting at least one-tenth rotation of the mechanical angle in units of 36 degrees using the data table shown in FIG. Convert.

Further, the third arithmetic circuit 15 calculates a highly accurate angular position θm ′ within one-tenth rotation of the mechanical angle based on the following equation.

Θm ′ = θm / 10 Then, by adding the high-precision angular position θm ′ to the upper digit z, a high-precision absolute angular position θ ′ representing one rotation as an absolute position can be detected.

In the above, n = 3 and p = 3, where the angle doubling angles of the two resolvers are n and m and the symmetry numbers are p and q.
And m = 10, q = 2, where n ≧ 2 and m ≧ 3
In addition, it can be realized if n and m are mutually prime natural numbers, p is a divisor of n other than 1, and q is a divisor of m other than 1.

The absolute angular position under such general conditions can be detected by the electric circuit shown in FIG. 3, but the constant part of the equations of the first, second and third arithmetic circuits 13, 14, and 15 and the ROM 16 Data table contents are different. The contents of these equations are shown below.

The radius R of the hollow portion is represented by the following function.

R = r−dr · cosnθ The following voltages Van, Vbn, Vam and Vbm are generated in the set of output windings of the nx and mx resolvers.

Vbn = J · Asinωt · sinθ Vbm = K · Asinωt · sinθ Vbm = K · Asinωt · sinθ, where J and K are constants.

The first arithmetic circuit 13 calculates an integer x based on the following equation.

X = INT (θn · m / 360 + 0.5−
(Θm · n / 360−INT (θm · n / 360))) When x ≧ m, x = x−m, and the second arithmetic circuit 14 calculates the integer y based on the following equation.
Is calculated.

Y = INT (θm · n / 360) Then, the ROM 16 converts the integers x and y into higher-order digits z for detecting at least 1 / m rotation of the mechanical angle in units of 360 / m degrees using a data table. Is done. An example of this data table is shown below.

In a table with three columns and mn rows, x
The integers from 0 to m-1 are repeatedly arranged n times. In the second column, integers from 0 to n-1 that y can take are arranged m times repeatedly. The third column is a number that is z, where n numbers increasing in increments of 360 / m continue. This table becomes the data table of the ROM 16. For example, when m = 5 and n = 2, xyz 0 0 0 1 1 1 0 2 0 2 7 3 1 7 2 4 0 0 4 0 1 1 1 4 10 10 16 2 1 216 3 0 288 4 1 288 is obtained.

Further, the third arithmetic circuit 15 calculates a highly accurate angular position θm ′ within one-mth rotation of the mechanical angle based on the following equation.

Θm ′ = θm / m Then, by adding a high-precision angular position θm ′ to the upper digit z, a high-precision absolute angular position θ ′ representing one rotation as an absolute position can be detected.

[0054]

As described above, according to the absolute encoder of the present invention, the mechanical structure and the magnetic structure of the rotor and the stator are the same every 1 / p and 1 / q rotation.
Due to the canceling effect, there is little influence on the position detection accuracy due to the misalignment between the rotor and the stator, and a high-precision absolute encoder in which no error occurs in the absolute angular position can be realized.

Further, since the mechanical structure of the rotor is the same every 1 / p and 1 / q rotations, vibration can be prevented even at high speed rotation.

Further, even if the number of double axes of the outer resolver is increased in order to increase the resolution, the influence of the misalignment between the rotor and the stator on the position detection accuracy is reduced by the canceling effect. , And a higher resolution absolute encoder can be realized.

Since the resolvers sharing the input shaft can be arranged on the same plane and concentrically without increasing the diameter, a small absolute encoder can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an absolute encoder according to the present invention.

FIG. 2 is a sectional view taken along line D-D 'of FIG.

FIG. 3 is a block diagram showing an example of an electric circuit of the absolute encoder according to the present invention.

FIG. 4 is a diagram for explaining the operation of the absolute encoder of the present invention.

FIG. 5 is a diagram showing data of a ROM according to the embodiment.

FIG. 6 is a cross-sectional view showing an example of a conventional absolute encoder.

FIG. 7 is a sectional view taken along line C-C 'of FIG.

FIG. 8 is a block diagram showing an electric circuit of a conventional absolute encoder.

FIG. 9 is a block diagram showing details of an interpolation circuit.

FIG. 10 is a timing chart of FIG.

FIG. 11 is a diagram illustrating the operation of a conventional absolute encoder.

[Explanation of symbols]

 Reference Signs List 1 input shaft 2 bearing 3 stator 11 timing generator 12 excitation signal generator 13 first operation circuit 14 second operation circuit 15 third operation circuit 16 ROM 17 fourth operation circuit 20 interpolation circuit 21, 22 amplifier 23, 24 sample・ And-hold circuit 25, 26 A / D converter 27 Fifth arithmetic circuit 30, 50 Inner resolver 31, 51 Inner stator 34, 44, 54 Input winding 35, 45, 55 Output winding 36, 46 Rotor 37, 57 hollow portion 40 outer resolver 41 outer stator 42, 52 pole teeth 47 teeth 301 to 312 pole teeth

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01D 5/00-5/252 G01D 5/39-5/62

Claims (3)

(57) [Claims] An absolute encoder for detecting an angular position within one rotation with an absolute value, wherein the first resolver whose axis double angle is nx (n is a natural number of 2 or more) shares the same input shaft with the first resolver. An absolute encoder, comprising: a second resolver disposed on a plane and on a concentric circle, having a shaft angle multiplier of mx (m is a natural number of 2 or more) and n and m having a prime relationship. 2. The first resolver according to claim 1, wherein said first resolver is rotated 1 / p (p
Comprises a stator and a rotor having the same mechanical structure and magnetic structure at every other natural number of 2 or more, and the second resolver is provided at every 1 / q rotation (q is a natural number of 2 or more). 2. The absolute encoder according to claim 1, further comprising a stator and a rotor having the same mechanical structure and magnetic structure. 3. The absolute encoder according to claim 1, wherein, in the positional relationship between the first resolver and the second resolver, the one with a larger axis double angle is arranged outside the other resolver.