JPH0820206B2 - Drive system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement in a technique for detecting a relative positional relationship between a fixed part and a movable part of an actuator in a drive system including the actuator.

(Prior Art and Its Problems) In order to perform drive control of a drive system including an actuator such as a motor, it is necessary to accurately know the relative positional relationship between the fixed portion and the movable portion of the actuator. A typical position detecting device used for such a purpose is an encoder. Among them, an optical encoder is used when it is necessary to obtain high resolution.

As is well known, the conventional optical encoder is provided with an array of slits on the disk surface and detects light transmitted through the slits. Therefore, the resolution of the conventional optical encoder is limited by the width of the slits and the distance between the slits, and the practical limit is about 8 μm as the slit width.

On the other hand, actuators used to drive industrial robots often require extremely high resolution. Therefore, when trying to further increase the resolution using a conventional optical encoder, a photodetection signal that changes in a trigonometric function according to the positional relationship between the slit and the photodetector is generated and this level is set. The position detection signal is obtained by division. However, since the divider used for such division is expensive, if the resolution is increased by the division as described above, the cost of the entire system increases. Further, in order to accurately obtain a trigonometric function light detection signal, the assembling accuracy and the mounting accuracy of the optical encoder must be increased, which complicates the manufacturing process of the system.

Further, in the conventional optical encoder, since the influence of the high-order diffracted light becomes relatively large when the slit width is narrowed, a mask having a window must be provided close to the disc. The gap between the disc and the mask is set to a small distance of about 10 μm in order to sufficiently exert the effect of shielding the high-order diffracted light by the mask. However, since the disc is attached to the movable portion side of the actuator, while the mask is fixed to the fixed portion side, the disc and the mask relatively rotate with the movement of the actuator. For this reason, when the disk or mask is deflected due to an external force or temperature change, and when the disk shakes due to the rotation, the disk and the mask collide with each other due to the rotation of the movable part, and they are destroyed. Therefore, such an optical encoder is difficult to use in a severe adverse environment such as vibration or temperature change. Further, because of problems such as rigidity, it is not possible to increase the disc diameter to improve the resolution. Even when the optical encoder and the actuator are connected by using a transmission mechanism such as a gear, the resolution is substantially reduced due to the influence of backlash and reduction in rigidity.

As described above, the conventional drive system including the optical encoder has a problem that the position detection resolution cannot be improved inexpensively and easily and the versatility is low.

(Object of the Invention) The present invention is intended to overcome the above-mentioned problems in the prior art, and an object of the present invention is to provide a drive system that can easily and inexpensively increase the resolution of position detection and has high versatility. To do.

(Means for Achieving the Object) In order to achieve the above object, the present invention provides an actuator for driving a driven body by a relative movement between a predetermined fixed portion and a movable portion, and the fixed member attached to the actuator. In a drive system including a position detection device that generates a position detection signal according to a relative positional relationship between a movable portion and the movable portion, the position detection device includes (a) a group of light reflection pits arranged according to a predetermined rule. And (b) a light reflector directly attached to the movable portion side, and (b) attached to a place having a fixed positional relationship with the fixed portion, and focusing on the light reflector by an automatic focus control device. Of the reflection type optical pickup that emits a detection light that connects the two and detects the reflected light obtained by the detection light being reflected by the light reflection pits and generates a light detection signal according to the detection result. And a position detection signal generated based on the light detection signal from the optical pickup.

The actuator is a direct drive motor, and the fixed part and the movable part are respectively
A stator and a rotor of the direct drive motor, the rotor being supported from the stator side by a single bearing.

Further, the light reflector and the optical pickup are mounted at positions near the bearing so as to face each other.

In the present invention, "directly attach the light reflector to the movable portion side" means to attach it without a transmission mechanism such as a gear. Therefore, mounting via a simple mounting member is not excluded from the present invention.

(Embodiment) A. Configuration of Actuator FIG. 1 is a schematic cross-sectional view of a main part of a drive system according to a first embodiment of the present invention. In this embodiment, a direct drive motor is used as an actuator. . In this figure, in this direct drive motor 1, a stator 3 is fixed to the inner peripheral portion of a cylindrical stator housing 2. The stator 3 includes a stator winding 5 wound through a slot (not shown) in the stator core 4.

On the other hand, a bearing 6 such as a cross roller bearing or a four-point contact type ball bearing is arranged on the inner peripheral surface of the upper end of the stator housing 2. This bearing 6
It is held between the inner circumferential stepped portion of the stator housing 2 and the fixed ring 7. The rotor shaft 9 is inserted inside the bearing 6.

The rotor shaft 9 is formed by a combination of the upper rotor shaft 9a and the lower rotor shaft 9b,
The rotor 8 is supported by them. Rotor 8
Has a rotor yoke 11 and a magnet 12 attached to the periphery thereof. In addition, the outer peripheral step portion of the upper rotor shaft 9a and the output flange 13 allow the bearing 6
The inner periphery of the is held.

Therefore, by applying an alternating current to the stator winding 5, the combined body of the rotor 8 and the output flange 13 is
The driven body (not shown) that rotates in the direction and is connected to the output flange 13 is rotationally driven.

Further, a bottom plate 14 having a circular plate shape with holes is attached to a lower portion of the stator housing 2, and a magnetic fluid seal, a rubber seal, or the like is provided between the inner peripheral surface 14a of the central hole of the bottom plate 14 and the lower rotor shaft 9b. The sealing material 15 is provided.
For this reason, the inside of the stator housing 2 is substantially hermetically sealed, and has a dustproof structure in which dust, water, chemicals, etc. existing outside the direct drive motor 1 do not enter the inside of the stator housing 2. .

The sealing material 15 is for sealing only, and the rotor 8 is supported by the single bearing 6.

B. Schematic configuration of position detection device In this direct drive motor 1, a stator 3
A detection unit of a position detection device that detects a relative positional relationship (rotational angle relationship) between the rotor 8 and the rotor 8 is provided. This detection unit has the light reflection disk 20, the optical pickup 30, and the optical sensors 40a and 40b as its main constituent elements.

Of these, the light reflection disk 20 has a disk shape with a hole and is directly attached to the outer peripheral stepped portion of the upper rotor shaft 9a, and its light reflection surface (described later) faces in the opposite direction to the bearing 6 ( In the illustrated example, it is arranged so as to face downward).

In addition, the optical pickup 30 and the optical sensor 40
The a and 40b are arranged at predetermined angular intervals around the circumference, and each is supported by the stator housing 2 by the support member 16. In other words, the optical pickup 30 and the optical sensors 40a and 40b are provided in a fixed positional relationship with the stator 4. The light detection heads of the optical pickup 30 and the optical sensors 40a and 40b face the light reflection surface of the light reflection disk 20, and the gap between these and the light reflection disk 20 is about 2 mm. .

This optical pickup 30 and the optical sensor 40a,
40b generates a light detection signal according to the relative angular positional relationship between the stator 3 and the rotor 8 according to the principle described later, and the light detection signal is sent to a signal processing circuit (not shown in FIG. 1). Forward.

C. Light Reflecting Disc Among these, the light reflecting disc 20 has a configuration similar to that used in acoustic engineering as an optical DAD (digital audio disc). That is, as shown as a partially enlarged sectional schematic view in FIG. 2A,
Linear pits 22 are formed on a surface of a transparent substrate 21 made of polycarbonate or the like according to a predetermined rule, and a light reflection film 23 such as an aluminum thin film and a protective layer 24 made of a hard resin are laminated on the surface. Therefore, the surface of the transparent substrate 21 is a light reflecting surface Q, and the pit 22 also has a property as a light reflecting pit.

The depth of the light reflection pit 22 is about n / 4 times the wavelength λ of the detection light L emitted from the optical pickup 30 (n is the wavelength λ
Of the transparent substrate 1). Therefore, the light reflected by the light reflection pit 22 and the light reflection film 23
The phase difference from the light reflected by the flat surface 25 of is π. As a result, in what area ratio the light reflection pit 22 and the flat surface 25 exist in the irradiation spot of the detection light L, in other words, according to the rotation position of the light reflection disk 20 in the x direction,
The intensity of the reflected light R including the interference components of these lights changes. Therefore, by detecting the intensity of the reflected light R, the relative angular positional relationship between the light reflection disk 20 and the optical pickup 30 is detected. For more information on such optical interference principles, see, eg, "Compact Disc Reader".
(Heitaro Nakajima et al., Ohmsha, 1982), page 90 et al.

FIG. 3 shows a light reflection pit 22 on the light reflection disk 20.
FIG. 6 is a diagram showing an arrangement state of the light reflection pits and the like. In this embodiment, the following light reflection pits and the like are provided on the light reflection disk 20.

Incremental type light reflection pit group 26 for giving an incremental type encode signal (A and B phases). The light reflecting pit group 26 is formed by arranging linear light reflecting pits 22 extending in the radial direction of the light reflecting disk 20 at equal angular intervals in the circumferential direction (in FIG. 3, FIG. 3). Only some of them are shown). The light reflection pits 22 have a width d of about 0.8 μm as shown in FIG. 4A, and the distance Δx between the adjacent light reflection pits is about 1.5 μm. For this reason,
By reading the light reflection pit 22 with the optical pickup 30, extremely highly accurate position detection is performed.

Such a linear (groove-shaped) light reflection pit 22 has a diameter of 0.8 μm in the photoetching of the transparent substrate 21, for example.
It can be manufactured by scanning and exposing a photoresist with a laser beam having a spot SP of m. Further, as shown in FIG. 4B, it is possible to form the light reflection pits 22 by arranging circular small pits PT. In this specification, all of the linearly extending light reflecting pits are collectively referred to as "streak-like light reflecting pits" in this specification.

By arranging the streak-like light reflection pits 22 at equal intervals in this way, the light reflection disc 20 in the radial direction y is formed.
Although the detection error due to the mounting error and the rotational vibration can be prevented, for example, the arrangement of rectangular light reflection pits may be used in the application in which the rotational vibration does not cause a problem.

A group of light reflection pits 27 for giving the Z phase (origin detection signal) of the incremental type encode signal. This is formed by the light reflection pits 22a to 22d provided at one place to several places (four places in the illustrated example) on the circumference. When detecting the origin, the light reflection pits 26a of A and B phases are formed. Used in combination. Particularly in the case of a large-diameter motor such as a direct drive motor, it takes a long time to detect the origin by slowly moving a relatively large load (driven object) for safety. The advantage of providing the light reflection pits 22a to 22d for detecting the origin is great.

On the other hand, this light reflection disk 20 has the above-mentioned light reflection pits.
In addition to 22,22a to 22d, dark color pattern groups 28 and 29 are provided. The dark color pattern groups 28 and 29 are used for the light reflection disk 2
The lower surface of the transparent substrate 21 of 0, or the transparent substrate 21 and the light reflection film 23.
It is formed by applying a dark color material (for example, a black material) to the boundary surface between and by printing or the like. The details of these dark color pattern groups 28 and 29 are as follows.

A group of dark color patterns 28 for giving an absolute type encoded signal. In the illustrated example, arc-shaped dark color patterns 28a to 2 which give 3-bit absolute type encode signals.
A group of dark color patterns 28 is formed by 8c. The dark color patterns 28a to 28c are read by the optical sensor 40a in terms of the contrast difference with the surroundings, and the absolute signal obtained thereby is used for mutual identification of the four light reflection pits 27a to 27d for origin detection. To be done.

A group of dark color patterns for commutation of stator windings 29. This is for obtaining the commutation information of the AC power to be applied to the stator winding 5 (FIG. 1) from the motor power supply circuit. In the illustrated example, an arc-shaped light-shielding pattern 29U, 29V, for performing three-phase two-pole commutation,
29W is included in this and these are read by the optical sensor 40b.

D. Optical Pickup and Optical Sensor The optical pickup 30 has three sets of unit pickups, of which one set of unit pickups 30a is schematically shown in FIG. 2A (other unit pickups are also included. Has a similar configuration). In FIG. 2A, the unit pickup 30a has a monochromatic light source 32 such as a laser diode, and the laser light (detection light) L from this light source 32.
However, the light is focused and irradiated on the light reflection surface Q in the light reflection disk 20 via the polarization beam splitter 33, the 1/4 wavelength plate 34 and the lens systems 35 and 36. The reflected light R obtained by reflecting this on the light reflecting surface Q produces lens systems 36, 35 and 1/4.
It passes through the wave plate 34 and reaches the polarization beam splitter 33 again.

Since the light passes through the quarter-wave plate 34 twice, the reflected light R
The polarization plane of is orthogonal to the polarization plane of the laser light before irradiation. Therefore, the reflected light R is reflected by the polarization beam splitter 33 and enters the photodetector 37, and the intensity thereof is detected by the photodetector 37.

As shown in FIG. 2B, the photodetector 37 has four light receiving surfaces P _{1 to} P ₄ . The photoelectric conversion signals obtained from each of the light receiving surfaces P _{1 to} P ₄ are added to each other to form a photodetection signal, and the difference in the sum of two diagonal components is obtained to obtain the focus error signal. Becomes This focus error signal is given to the automatic focus control device (focus servo) 31. The automatic focus control device 31 changes the value of the current passed through the focus coil 38 based on this focus error signal. As a result, the magnitude of the magnetic interaction between the focus coil 38 and the magnetic circuit including the magnet 39a and the yoke 39b changes, and the focus coil 38 moves in the H direction. Since the lens system 36 is connected to the focus coil 38, the lens system 36 also moves in the H direction (direction perpendicular to the light reflection surface Q) along with the above movement.
This movement is stopped when the level of the focus error signal becomes zero (that is, the focused state). As a result, even if the distance between the light reflection disk 20 and the optical pickup 30 changes, the laser light L is always focused on the light reflection surface Q.

Of the three unit pickups, the first and second unit pickups are used to detect the A-phase and B-phase components of the incremental type encode signal, respectively. Therefore, as shown in FIG. 5, the light spots SPA and SPB from these are irradiated toward the arrangement position of the light reflection pit group 26. However, as is well known, since the B phase of the encode signal for identifying the rotation direction needs to have a predetermined phase difference from the A phase, the light spot SP
The irradiation positions of A and SPB have a deviation of (2N + δ) π ... ing.

The light spots SPZ from the remaining one set of unit pickups are irradiated toward the array position of the light reflection pit group 27 for Z phase detection.

Of these, as the optical spots SPA and SPB, a main spot and a tracking spot used in an optical pickup for a CD (compact disc) can be used. That is, in the optical pickup for CD, a main spot SPM for data reading / focusing as shown in FIG. 6 and two tracking spots SP1 and SP2 sandwiching the main spot SPM are provided. However, of these, the main spot SPM and one tracking spot SP1 are used as light spots for the A phase and the B phase, respectively. The phase adjustment in this case is as follows in which the line segment l ₁ connecting the main spot SPM and the tracking spot SP ₁ is as follows with respect to the arrangement direction x of the light reflection pits 22 (circumferential direction of the light reflection disk 20). Make sure that the angle is such that the relationship is satisfied.

L ₁ cos θ = (N + δ / 2) Δx (2) where L ₁ is the distance between the main spot SPM and the tracking spot SP ₁ (for example, 30 μm).

In this way, the mutual distance L ₂ between the main spot SPM and the tracking spot SP1 in the x direction is (N + δ /
2) Δx, and a phase difference of (2N + δ) π can be obtained based on the arrangement interval Δx of the light reflection pits 22. In this case, the other tracking spot SP2
Is not used.

On the other hand, the first optical sensor 40a for obtaining the absolute type encoding signal and the second optical sensor 40b for obtaining the commutation signal are arranged so that the irradiation light L'is reflected by the light reflecting disk 20 as shown in FIG. Is irradiated onto the surface of the optical disk, the reflected light R'is separated by the half mirror 41, and the intensity thereof is detected by the photodetector 42. In other words, since the absolute type encode signal and commutation signal are sufficient with relatively coarse accuracy, the reflected light due to the contrast difference (difference in light reflectance) between the dark color patterns 22a to 22c, 29U to 29W and the surrounding density. By capturing the intensity change of R ′, the dark color patterns 22a-2
It suffices to detect the presence of 2c, 29U-29W. Of course, it can be used in combination with the light reflection pit, the optical pickup, and the automatic focus control device, but the cost can be further reduced by using this embodiment.

E. Signal Processing Circuit With the above configuration, the optical detection signals output from the optical pickup 30 and the optical sensors 40a and 40b are transferred to the signal processing circuit 50 shown in FIG. The signal conversion circuit 51 provided in the signal processing circuit 50 performs the following signal conversion.

An incremental type encode signal (position detection signal) D _inc is obtained based on the light detection signals S _A and S _B from the A-phase and B-phase unit pickups. This is performed by signal processing similar to that of the conventional incremental encoder. Further, the origin detection signal D _Z is output when a predetermined A-phase (or B-phase) pulse is detected within the period in which the light detection signal S _Z from the Z-phase unit pickup is observed.

A coarse absolute type encode signal D _abs is obtained from the absolute light detection signals S _{0 to} S ₂ . As described above, this absolute type encode signal D _abs is
It is used for mutual identification of the plurality of Z-phase light reflection pits 22a to 22d.

In this embodiment, the signal conversion circuit 51 is provided with an error detection circuit that detects a defective generation state of a light detection signal from the optical pickup 30 and generates an error signal ER.
A configuration example of this error detection circuit is shown in FIG. In FIG. 9, digital photodetection signals D _A and D _B obtained by binarizing the A-phase and B-phase photodetection signals S _A and S _B are supplied to frequency / voltage converters 61 and 62. Therefore, when the incremental type photodetection signals S _A and S _B are normally applied and the digital photodetection signals D _A and D _B are repetitive pulses,
The output voltages V ₁ and V ₂ of the frequency / voltage converters 61 and 62 are voltages having a logical value “1”. These voltages V ₁ and V ₂ are applied to one-input inverting AND circuits 63 and 64, and the other input of these AND circuits 63 and 64 drives the motor from the position controller 52 (Fig. 8). The control signal V _C is input. And an
The output voltages V ₃ and V ₄ of the D circuits 63 and 64 are given to the OR circuit 65.

Therefore, (a) the motor drive control signal V _C is “0” and the rotor 8 is stopped, or (b) the motor drive control signal V _C is “1” and the rotor 8 is rotating, And the digital light detection signals D _A and D _B are normally generated (V ₁ = V ₂
= “1”), the error signal ER is “0”, and “normal” is detected.

On the other hand, consider a case where at least one of the digital light detection signals D _A and D _B is “0” although the motor drive control signal V _C is “1”. Then, one or both of the voltages V ₁ and V ₂ become “0”, so that the error signal ER becomes “1” and the defective occurrence of the photodetection signals S _A and S _B is detected.

Such an error detection circuit can also be realized by the following configuration. That is, first, it is noted that the light detection signals S _A and S _B during the rotation of the rotor 8 become the analog repetitive pulse signal V _A1 or the sinusoidal repetitive signal V _A2 as shown in FIG. 10 (a). . These light detection signals S _A and S _B reflect the intensity of the reflected light R, but it is possible to set the minimum value S _{min of the} repetitive waveform to a finite value that is not “0”. It is possible. This means, for example, that the depth of the light reflection pit 22 is n / 4 of the wavelength of the laser light L.
This can be achieved by making the depth slightly different from the double and imperfectly canceling the interference. Therefore, the photodetection signals S _A and S _B are set to the threshold value S _TH1 (Fig. 10 (a)).
Compared with digital light detection signals D _A , D _B (Fig. 10 (b))
In addition to obtaining the above, when compared with the second threshold value S _TH2 set between the minimum value S _min and the zero level, these light detection signals S _A and S _B cannot be detected due to the generation failure. Signal S _A ,
It is possible to detect when S _B has fallen to the zero level.

FIG. 11 shows an example of a circuit that realizes such a principle.
The comparators 66 and 67 detect that the light detection signals S _A and S _B are the threshold S.
_When it becomes _TH2 or less, signals V ₅ and V ₆ which become “1” are generated, and based on this, the error signal ER from the OR circuit 68 becomes “1”.

The respective signals D _inc , D _Z , of FIG. 8 obtained as described above,
D _abs , ER is output to the position controller 52 that controls the motor rotation position.

Remaining signals output from the signal conversion circuit 51 in FIG.
D _com is a commutation signal of three-phase power to the stator winding 5. That is, dark patterns 29U, 29V, light detection signal S _U by the reading of 29W, S _V, although S _W is obtained, these light detection signals S _U, S _V, commutation signals in response to a level change of the S _W D _com is generated, and based on that, commutation of electric power to the stator winding 5 in the motor power supply circuit 53 is performed.

F. Operation of First Embodiment In the first embodiment having the above configuration, the rotor 8 rotates based on the motor drive control signal V _C, and various encode signals D _inc , D _Z according to the rotation angle thereof. , D _abs and commutation signal D _com are generated. In this operation, since the light reflection pits 22 are arranged in a very high density, the incremental type encode signal D _inc becomes an extremely high precision signal (for example, 60,000 to 1,000,000 pulses / revolution). Also,
Since the automatic focus control device 31 is used, even if a mounting error or rotational deformation occurs in the light reflecting disk 20 or the optical pickup 30, highly accurate detection is always performed. Since such an automatic focus control device 31 is provided, the problem of defocusing does not occur and the light reflection disk
The distance between 20 and the optical pickup 30 can be made relatively large. As a result, even if the light reflecting disk 20 bends to some extent due to an external force applied to the rotor, it will not collide with the optical pickup 30 and be damaged. Since the light reflecting disk 20 is directly attached to the rotor 8 side, there is no detection error due to backlash or the like as in the case of using a gear or the like. Since the light-reflecting pit 22 has a linear shape extending in the radial direction of the light-reflecting disk 20, it is possible to prevent the missed reading due to the shake in the radial direction.

Further, in this first embodiment, since the light reflection disk 20 is provided in the dustproof space inside the stator housing 2, dust from the outside of the motor adheres to the surface of the light reflection disk 20 and reduces the detection accuracy. Nothing. Since the reflection surface of the light reflection disk 20 is provided in the direction opposite to the direction toward the bearing 6 in FIG. 1, the splash of grease from the bearing 6 is unlikely to adhere to the reflection surface.

Since the rotor shaft 9 is supported by the stator housing 2 by the single bearing 6 and the light reflection disk 20 is mounted in the vicinity thereof, an error due to tilting or swinging of the rotor 8 is unlikely to occur. Further, before the rotor yoke 11 and the stator 3 are mounted, the mounting position of the light reflecting disk 20, the optical pickup 30, etc. can be adjusted.

G. Second and Third Embodiments FIG. 12 is a diagram showing a second embodiment of the present invention. In this embodiment, a light reflecting disk 20 is mounted on the opposite side of the bearing 6 with the rotor 8 in between. Correspondingly, the optical pickup 30 and the optical sensors 40a and 40b are also fixed to the opposite side of the bearing 6 with the rotor 8 in between.

By doing so, the optical pickup 30 and the like are installed in a place where the heat dissipation condition for the heat generation of the stator 3 is good. Further, even if the bearing 6 generates heat due to the rotation of the rotor 8, the heat is rarely propagated to the light reflecting disk 20, the optical pickup 30, etc., so that errors and deterioration due to temperature rise can be effectively prevented. Furthermore, the influence of grease splash from the bearing 6 is further reduced.

FIG. 13 shows a third embodiment of the present invention. In this embodiment, the light reflecting disk 20 is attached to the output flange 13,
The optical pickup 30 and the optical sensors 40a and 40b are also fixed to the inner wall of an annular member 18 having a substantially L-shaped cross section attached to the upper portion of the stator housing 2. This has the advantage that the optical pickup 30 and the light reflecting disk 20 can be adjusted after the motor is assembled. Further, since the position detection is performed in the vicinity of the bearing 6, there is almost no influence such as a fall. The influence of heat generation of the motor is further prevented.

H. Modifications Although the respective embodiments have been described above, the present invention is not limited to the above embodiments, and the following modifications can be made.

The light reflector does not have to be disc-shaped, but may be drum-shaped or the like. In the case of the drum shape, the effect that the motor can be downsized is added. Further, in a drive system including a linear actuator, it may be plate-shaped or band-shaped. Furthermore, as shown in Figure 14, the light reflection pit
A tape-shaped cord band 72 in which 71 are arranged is a ring-shaped support.
It may be attached to the outer periphery of 73. In this case, the break (joint) 74 of the cord band 72 is present. However, in a direct drive motor or the like used in an industrial robot, it is not necessary for the rotor to rotate 360 °, and in many cases it is sufficient to rotate the rotor within an angle range of 360 ° or less. Therefore, if the cut 74 is made to correspond to the non-rotational angle range portion of the rotor, the position detection will not be affected by the cut 74.

The size of the light reflection pit 22 can be made significantly smaller than that of a conventional slit, but on the other hand,
The probability that the light reflection pit 22 is missed will also increase to some extent. In the application where the detection accuracy is required to be particularly strict, it is necessary to prevent such a missed reading, and for that purpose, for example, the following may be performed. That is, first, as shown in FIG. 15, three or more light spots SP _{a to} SP _c are prepared as light spots for obtaining one signal (for example, A-phase signal). Then, the majority of three or more photodetection signals obtained based on the reflection of these light spots SP _{a to} SP _c is taken, and thereby, it is determined whether or not the light reflection pit 22 is detected. Such a majority circuit itself can be formed by a simple logic circuit. In this way, not only the light reflection pits 22 can be missed but also erroneous detection due to dust or the like can be prevented.

In each of the above embodiments, a light reflector, an optical pickup, etc. are incorporated in the direct drive motor, thereby effectively utilizing the space inside the direct drive motor. It may be provided as an independent encoder. Also in this case, the light reflector is directly attached to the rotor (movable part) side in order to prevent the influence of backlash.

In the direct drive motor of FIG. 1, if the output flange 13 and the fixed ring 7 are also sealed, the grease splashing on the bearing 6 will not come out of the motor. Therefore, in this way, the dustproof property of the clean room is improved when the motor is used in a clean room or the like. In addition, if the inside of the motor is air-purged by using the dry air supplied to the factory and the line filter, the light reflection disk, etc. can be protected from dust damage and temperature rise.
It can also protect against condensation.

(Effects of the Invention) As described above, according to the present invention, the light reflector in which the light reflection pits are arrayed is directly attached to the movable portion side of the actuator, and the reflection type having the automatic focus control device is provided. Since this light reflection pit is read by the optical pickup, the resolution of position detection in the drive system can be easily increased significantly. In addition, since it does not require a complicated signal processing circuit, it is inexpensive, and since the distance between the light reflector and the optical pickup can be relatively large, it is resistant to deformation and vibration due to external force, and its versatility is extremely high. There is.

Further, since the light reflector and the optical pickup are mounted in the vicinity of the bearing supporting the rotor, errors due to tilting or wobbling of the rotor are less likely to occur, and further, before mounting the rotor yoke or the stator, the light reflecting disk or The mounting position of an optical pickup or the like can be adjusted.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a main part of a direct drive motor used in an embodiment of the present invention, FIG. 2A is a view showing a schematic configuration of a light reflection disk, an optical pickup and an automatic focus control device, and FIG. 2B. Is a diagram showing a light receiving surface of a photodetector used for an optical pickup, FIG. 3 is a schematic plan view of a light reflecting disk, FIGS. 4A and 4B are explanatory diagrams of a light reflecting pit, FIG. FIG. 6 is a diagram showing the relationship between the light reflection pits and the light spot of the detection light, FIG. 7 is an explanatory diagram of a dark color pattern and an optical sensor, FIG. 8 is a block diagram of a signal processing circuit, and FIG. 11 and 12 are circuit diagrams of an error signal generating circuit, FIG. 10 is a waveform diagram showing the principle of error signal generation, and FIGS. 12 and 13 are second and third embodiments of the present invention, respectively. Of the direct drive motor used in the example Part schematic cross-sectional view, FIG. 14 and FIG. 15 is an explanatory view of a modification of the present invention. 1 ... Direct drive motor, 2 ... Stator housing, 3 ... Stator, 8 ... Rotor, 9 ... Rotor shaft, 20 ... Light reflecting disk, 22, 22a-22d ... Light reflecting pit, 30 ... Optical pickup, 31 …… Automatic focus control device, 40a, 40b …… Optical sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H02K 11/00

Claims (4)

[Claims] 1. An actuator for driving a driven body by a relative movement between a fixed portion and a movable portion, and position detection according to a relative positional relationship between the fixed portion and the movable portion, which is attached to the actuator. A drive system including a position detection device that generates a signal, wherein the position detection device has a group of light reflection pits arranged according to a predetermined rule, and a light reflector directly attached to the movable portion side, , Is attached to a position having a fixed positional relationship with the fixed portion, and irradiates detection light for focusing on the light reflector by an automatic focus control device, and the detection light is reflected by the light reflection pit A reflection-type optical pickup that detects reflected light obtained by generating a light detection signal according to the detection result, and the position detection signal is a light detection signal from the optical pickup. The actuator is a direct drive motor, the fixed part and the movable part are a stator and a rotor of the direct drive motor, respectively, and the rotor is a single bearing from the stator side. A driving system, which is supported, wherein the light reflector and the optical pickup are mounted at positions near the bearing so as to face each other. 2. The drive system according to claim 1, wherein the light reflection pit group is an incremental type light reflection pit group formed by arranging linear light reflection pits at equal intervals. 3. The drive system according to claim 1 or 2, further comprising means for detecting an error generation state of the light detection signal and generating an error signal. 4. The light reflector and the optical pickup,
The drive system according to any one of claims 1 to 3, wherein the drive system is mounted opposite to each other at a position opposite to the bearing with the rotor interposed therebetween.