JP4517058B2 - Micro servo motor unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a micromotor used for medical devices such as endoscopes and micromachines, and more specifically, the rotational position, rotational direction, and rotational speed can be controlled with a unit outer diameter of 3 mm or less. The present invention relates to a micro servo motor unit.
[0002]
[Prior art]
Conventionally, in a servo motor with an encoder, an attached encoder is attached to the non-output shaft side of the motor, and the rotation speed, rotation direction, rotation position, etc. of the motor are generally controlled according to information obtained from the encoder. . There are two types of encoders: an absolute type that detects an absolute rotation amount based on its output signal format, and an incremental type that outputs a relative rotation amount.
[0003]
Of these two methods, an incremental type is often used to control a small DC motor, and as will be described later, there are a reluctance type, an optical type, and a magnetic recording type as an incremental type encoder.
[0004]
FIG. 6 is a block diagram showing a system configuration of a conventional software servo. Here, an H-type driver 1 composed of four transistors is connected to a DC power source, and an output of the H-type driver 1 is connected to a DC motor 2. An encoder 3 is directly connected to the shaft of the DC motor 2, and the two-phase output of the encoder 3 is input to the pulse generator 4.
[0005]
Furthermore, the speed detector 5 is constituted by a counter with zero clear, which is zero-cleared every fixed time, and a value immediately before the next zero clear, that is, a count value during the sampling time, is used as a speed feedback value. It is the structure which feeds back to.
[0006]
The position detector 6 is constituted by an up / down counter, and detects the rotational position of the DC motor 2 by up / down according to the up / down pulse signal of the pulse generator 4 to obtain a position feedback value. It is the structure which feeds back to.
Reference numeral 8 described later is a user command unit, reference numeral 9 is a PWM circuit, and reference numeral 10 is a pre-drive circuit.
[0007]
FIG. 7 is a timing chart showing input / output signals of the pulse generator 4. As shown in the figure, the encoder normally has two phases and outputs rectangular waves having a phase difference of 90 degrees from each other. In synchronization with the rise and fall, an up pulse is generated when the A phase of the encoder advances from the B phase, and a down pulse is generated when it is opposite. The up / down pulse is input to the speed detector 5 or the position detector 6, and the speed feedback value and the position feedback value are supplied to the microcomputer system 7. In order to know the absolute position, a Z phase is further provided, and the number of pulses from there is counted.
[0008]
On the other hand, commands such as return to origin, speed control, position control, etc. are input from the user command section 8 to the microcomputer system 7, and calculation processing is performed using the speed feedback value and position feedback value described above. Is transmitted to the circuit 9. In the PWM circuit 9, the duty value is subjected to pulse width modulation, the signal is amplified by the pre-drive circuit 10 as a transistor ON / OFF signal, and the final stage transistor is driven.
[0009]
As described above, the encoder is used for software servo because it can detect three types of information: speed, rotation direction, and rotation position.
[0010]
FIG. 8 shows examples of various encoders in the incremental type. In the figure, (a) is a reluctance encoder in which the magnetic gear 11 rotates, and the resistance value of the magnetoresistive element 12 changes due to the unevenness, and this is detected by the comparator 13.
[0011]
(B) is an optical encoder, in which a rotating disk 16 and a fixed disk 17 are arranged between the light-emitting diode 14 and the phototransistor 15, and the slits provided on the rotating disk 16 and the fixed disk 17 directly connected to the motor shaft are opened and closed. The output voltage of the phototransistor 15 changes, and this is output by the comparator 13.
[0012]
(C) is a magnetic recording encoder, and the resistance value of the magnetic sensor 19 changes with the rotation of the shaft by the rotating drum 18 coated with the magnetic recording medium attached to the motor shaft and the magnetic sensor 19 on the fixed side. This is output by the comparator 13 and a pulse is generated at every fixed angle.
Of these methods, optical encoders are generally used in many cases.
[0013]
[Problems to be solved by the invention]
However, in a small motor using a conventional encoder as shown above, no matter which encoder method is adopted, a disk-shaped rotating disk or rotating drum is always attached to one end of the rotating shaft of the motor. As described above, since the component (attached rotating body) protruding from the output shaft is attached to the shaft end, there are the following problems in adopting this structure in the micro motor.
[0014]
That is, in order to detect the three types of information of the rotation speed, the rotation direction, and the rotation position, three pairs of pattern sensors for obtaining information for the three phases A, B, and Z are required. However, in the case of an ultra-compact motor with an encoder having a motor outer diameter of, for example, φ3 mm or less, it is extremely difficult in terms of space with an arrangement configuration that detects all of the A, B, and Z phases.
[0015]
Further, in such a small motor, the output torque and mechanical rigidity decrease as the diameter decreases, and an additional rotating body such as a rotating disk or a rotating drum as described above can be connected to a pole having an outer diameter of φ0.3 mm, for example. When it is mounted on a small-diameter motor shaft, the drive responsiveness decreases significantly as the rotor inertia increases, and the dynamic unbalance of the rotor due to the mounting accuracy of the attached rotating body or the processing accuracy of the rotating body itself is reduced. Therefore, the amount of vibration of the motor output shaft and the bearing loss are increased.
[0016]
The present invention has been made in view of the above, and even if the motor is an ultra-compact with an outer diameter of 3 mm or less, it prevents deterioration of response performance and increases the amount of runout of the motor output shaft and bearing loss. In addition to blocking, the object of the present invention is to make it possible to obtain all information on the rotational speed, the rotational direction, and the rotational position.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, in the micro servo motor unit according to claim 1, an ultra-compact micro motor comprising an electromagnetic motor, a speed reduction means and an optical encoder both having an outer diameter of 3 mm or less, and a driver thereof In the micro servo motor unit consisting of
Provided on the part of the shaft is a reflecting surface that reflects light in a state of not projecting from the outer diameter of the shaft on the side opposite to the output shaft of the electromagnetic motor , the speed reduction means that decelerates at a predetermined reduction ratio. When the output shaft rotates, the optical encoder that projects light on the reflecting surface, receives the reflected light, and outputs the Z phase in response to the light ON / OFF signal, and forward / reverse driving the electromagnetic motor. And a driver having a function of outputting a pulse signal synchronized with a change in counter electromotive voltage or coil current generated when the electromagnetic motor rotates.
[0018]
According to the present invention, even for an ultra-small electromagnetic motor having an outer diameter of about 3 mm or less, for example, a through hole or a shaft end that does not have a convex shape projecting from the outer diameter of the output shaft to the opposite output shaft side. A reflection surface is provided on the part, and when the output shaft rotates, the part is irradiated with light, and the transmitted light or reflected light is received to obtain a Z-phase signal. The Z-phase signal (absolute origin) can be acquired from the movement, and the rotation direction can be grasped by actively rotating the axis forward / reversely with the driver rotation direction switching function. By using the pulse signal output synchronized with the back electromotive voltage or the change of the coil current and the Z-phase signal, the rotational speed and the rotational position can be detected. In addition, by providing the rotating part that performs the encoder function so that it does not protrude from the outer diameter of the output shaft, the moment of inertia can be reduced compared to the conventional mounting method using a rotating disk or rotating drum. It is possible to eliminate the increase without any increase.
[0020]
Further, for example, an outer diameter of about .phi.3 mm, or less even tiny electromagnetic motor, its motor output shaft side, by providing an optical encoder for Z-phase output, Z for controlling the rotational position A phase signal can be obtained.
[0021]
According to the present invention, the output shaft of the electromagnetic motor is provided with a speed reduction means for reducing the speed with a predetermined reduction ratio by, for example, a planetary gear group, so that the movement of the servo motor output shaft (the output shaft of the speed reduction means) is prevented. The number of FG pulse outputs increases, enabling more accurate control.
[0022]
In the micro servo motor unit of the present invention, the electromagnetic motor, the encoder, and the speed reducing means have an outer diameter of 3 mm or less, and are used for medical devices such as endoscopes, micro machines, and the like. The most suitable motor dimension is inevitably an outer diameter of 3 mm or less.
[0023]
In the micro servo motor unit according to claim 2 , the encoder includes a partial reflecting surface formed on the opposite output shaft side of the electromagnetic motor so as not to protrude from the outer diameter of the shaft, and the output shaft. And an optical fiber that guides light from a light source to the reflecting surface, and a light receiving means that receives the light projected by the optical fiber and reflected by the reflecting surface. .
[0024]
According to this invention, for example, the end of the motor rotation shaft on the side opposite to the output shaft of the electromagnetic motor is cut into an inclined surface to form a reflecting surface, and the reflecting surface is irradiated with light from the axial direction via the optical fiber, The reflection direction rotates with the rotation of the motor shaft and the micro-encoder is configured to detect the light by the light receiving means arranged in the circumferential direction of the reflected light. Therefore, an ultra-small encoder that eliminates the increase in moment of inertia is realized.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of a micro servo motor unit according to the present invention will be described below in detail with reference to the drawings.
In addition, this invention is not limited to this embodiment, A structure is taken as an example.
[0030]
FIG. 1 is a block diagram showing a configuration of a micro servo motor unit according to an embodiment of the present invention. In the figure, reference numeral 100 denotes an electromagnetic motor such as a three-phase sensorless brushless motor, reference numeral 110 denotes an optical encoder provided to perform a Z-phase output as described later, and reference numeral 120 denotes a driver for driving the electromagnetic motor 100. Reference numeral 121 denotes a forward / reverse switching unit that performs forward / reverse switching, and reference numeral 122 denotes a motor reverse that generates and outputs a FG (Frequency Generator) pulse synchronized with a change in the back electromotive voltage generated when the electromagnetic motor rotates. An electromotive voltage FG pulse output unit, and reference numeral 130 is a DC power source.
[0031]
Reference numeral 101 is a U-phase output line, reference numeral 102 is a V-phase output line, reference numeral 103 is a W-phase output line, reference numeral 104 is a stator coil middle line, reference numeral 105 is an encoder power line, reference numeral 106 is an encoder 110 Z-phase signal line. Reference numeral 107 denotes a forward / reverse switching terminal for instructing the rotation direction, and the forward / reverse switching is normally performed depending on the H level or L level (or open). Reference numeral 108 denotes an FG pulse output terminal for outputting a pulse signal synchronized with a change in the back electromotive voltage, and reference numeral 109 denotes a Z-phase pulse output terminal for outputting a Z-phase signal which is an absolute origin. Used for.
[0032]
This three-phase sensorless brushless motor has a configuration in which a normal three-phase brushless motor detects a magnetic pole, that is, a rotor position by a magnetic pole sensor such as a hall element, and detects the position of the rotor by detecting a counter electromotive voltage generated in a stator coil. It is the composition which grasps. The back electromotive voltage FG pulse output unit 122 of the motor generates a rectangular FG pulse synchronized with the change of the back electromotive voltage of the electromagnetic motor 100 and outputs it from the FG pulse output terminal 108.
[0033]
In other words, when the rotor magnetic pole crosses the coil, a counter electromotive voltage is generated in the coil. Therefore, the rotation speed is detected by generating a FG pulse synchronized with the change using the change in the counter electromotive voltage. Is possible.
[0034]
For example, when the rotor magnet is configured to monitor one stator coil with two poles, one short FG pulse is output per rotation, or the rotor magnet is configured to monitor three stator coils with four poles. In this case, 6 FG pulses are output per rotation. Therefore, the number of rotations can be grasped by counting the number of pulses during the sampling time.
[0035]
Further, the rotational position can be grasped by using the Z-phase signal output from the Z-phase pulse output terminal and counting the number of FG pulses from the Z-phase signal. The frequency signal (pulse) can be converted into a voltage signal by an external F / V converter (not shown) and used as an analog speed signal.
[0036]
As described above, according to the present invention, the control is the same as when all three-phase (A / B / Z-phase) output encoders are mounted, that is, the speed and the rotation, even though the servo motor has an outer diameter of 3 mm or less. It is possible to control all directions and rotational positions.
[0037]
Next, a specific example of the encoder 110 will be described. FIG. 2 is an explanatory diagram illustrating a first configuration example of the encoder 110 according to the embodiment of the present invention. In the figure, reference numeral 111 denotes a motor shaft, reference numeral 111a denotes a small-diameter through hole provided orthogonal to the motor shaft 111, reference numeral 113 denotes a light source using an LED (light emitting diode), LD (laser diode), etc. Reference numeral 114 denotes a light receiving sensor using a light receiving element such as a phototransistor, and reference numeral 115 denotes a circuit board connecting them.
[0038]
The combination of the light source 113 and the light receiving sensor 114 may be any of a light emitting diode and a phototransistor, a light emitting diode and a photo IC, a laser diode and a photo IC, and the like. Further, the light emitting source 113 and the light receiving sensor 114 are integrally formed in a U-shaped configuration, and the motor shaft 111 is disposed so that the through hole 111a is on the optical axis between them.
[0039]
FIG. 3 shows a state of one end of a motor shaft 111 used as an encoder. In FIG. 3, (a) shows a through-hole type, and (b) shows a slit-type shape. In this embodiment, the outer diameter of the electromagnetic motor 100 is about φ2 mm, the outer diameter of the motor shaft 111 is φ0.3 mm, the diameter of the through hole 111a and the width of the slit 111b are φ0.15 mm and 0.15 mm. In this embodiment, the through hole 111a and the slit 111b are formed by fine processing of a laser processing machine capable of processing a beam diameter of about 10 μm, and the diameter of the through hole 111a and the width of the slit 111b are approximately the same as the motor. One half of the outer diameter of the shaft 111 was used. This setting is arbitrary, and some dimensional changes are not limited unless there is a functional problem.
[0040]
By providing these through holes 111a and slits 111b so as not to protrude with respect to the outer diameter of the motor shaft 111, it was possible to eliminate the increase in the moment of inertia accompanying the increase in the mass in the radial direction.
[0041]
In this way, the motor shaft 111 is provided with the through-hole 111a or the slit 111b, the light source 113 is provided at a corresponding position on the circumference, and the light from the light source 113 that has passed through the through-hole 111a or the slit 111b is received. The light receiving sensor 114 is provided at a position, that is, a position on the circumference facing the light source 113.
[0042]
With such an encoder configuration, the light output from the light source 113 is transmitted / blocked through the through hole 111a or the slit 111b by the rotation of the motor shaft 111, and the light receiving sensor 114 is used as a light ON / OFF signal. Is input. The output of the light receiving sensor 114 is input to the Z-phase input terminal, and a Z-phase pulse is output from the Z-phase pulse output terminal 109.
[0043]
FIG. 4 is an explanatory diagram illustrating a second configuration example of the encoder according to the embodiment of the present invention. In the encoder shown in FIG. 4, a reflection surface 111c inclined at 45 degrees is formed at the tip of the motor shaft 111 on the opposite output side, and the optical fiber 116 connected to the light source so that the optical axis is coaxial with the motor shaft 111. And a light receiving sensor 114 disposed to face the reflecting surface 111c in the radial direction. Further, depending on the form of use, the optical fiber 116 and the light receiving sensor 114 may be replaced with each other. The reflecting surface 111c is formed by performing a mirror finish on the cut surface after cutting at a predetermined angle.
[0044]
The optical fiber 116 is made of two types of materials having different refractive indexes. For example, the outer diameter of the coated wire is about φ1 mm, and the diameter of the core portion (core portion through which the optical signal passes) is 5 to 7 μm. A clad portion having a diameter of φ125 μm around the core is used, but is not limited thereto.
[0045]
In the encoder configured as described above, the inclined reflecting surface 111c is rotated by the rotation of the motor, and the light from the optical fiber 116 is guided to the light receiving sensor 114. When the reflecting surface 111c comes to the position shown in the figure, the light from the optical fiber 116 is received by the light receiving sensor 114. However, in other positions, no input to the light receiving sensor 114 is performed. Shading is repeated, and a light ON / OFF signal is obtained.
[0046]
Therefore, even in a very small space with a motor outer diameter of 3 mm or less, a micro-encoder that detects the Z phase is realized by adopting the encoder configuration as shown in FIG. 2 or FIG. In addition, since there is no need to attach an attached rotating body such as a rotating disk or a rotating drum to the motor shaft 111 as in the conventional case, the responsiveness decreases as the rotor inertia moment increases, the mounting accuracy or rotation of the attached rotating body Since the saw-like movement of the output shaft (motor shaft) accompanying the increase in the dynamic unbalance of the rotor due to the machining accuracy of the body itself is suppressed, the increase in run-out and bearing loss can be eliminated.
[0047]
Next, FIG. 5 is explanatory drawing of the structural example with a 3rd reduction mechanism which shows the example of a combination of the motor with an encoder concerning embodiment of this invention. This shows a case where a speed reduction mechanism is attached to the electromagnetic motor 100 described above, (a) is a side external view, and (b) is an AA sectional view of the gear box 140 portion. That is, a geared motor in which a speed reduction mechanism such as a gear box 140 is attached on the motor output shaft side is designed to reduce speed and increase torque.
[0048]
Here, a planetary gear type reduction gear is used as a reduction mechanism, in which three planetary gears 141 mesh with a pinion gear 142 attached to the motor output shaft to reduce the speed. If allowed, a normal spur gear speed reduction mechanism or a worm and worm wheel speed reduction mechanism may be used.
[0049]
For example, as the electromagnetic motor 100, the gear box 140 of the reduction mechanism having a gear ratio of 79: 1 is attached to the three-phase sensorless brushless motor described in FIG. In this case, assuming that a three-phase sensorless brushless motor shaft outputs one FG pulse per revolution, the relationship between the servo motor output shaft (gear output shaft) and the FG pulse is as follows.
[0050]
That is, when there is no gearbox (no speed reduction mechanism), one pulse is output when the brushless motor makes one revolution, whereas when a speed reduction mechanism with a gear ratio 79: 1 is provided, the servo is 79 pulses are output per rotation of the motor output shaft (output shaft of the speed reduction means). Whether it is a single electromagnetic motor or a geared motor equipped with a speed reduction mechanism, it can be said to be one servo motor that transmits rotational force to a load. Therefore, the number of FG pulses output per rotation of the servo motor output shaft increases, and the resolution can be improved.
[0051]
In this embodiment, the three-phase sensorless brushless motor 100 having an outer diameter of φ2 mm and the gear box 140 and the encoder 110 having an outer diameter of φ2.4 mm have been described as an example. It goes without saying that it can be applied to any type of micro-motor.
[0052]
【The invention's effect】
As described above, according to the micro servo motor unit according to the present invention, for example, the outer diameter of the output shaft instead of the encoder rotating body conventionally attached to the non-output shaft side of the ultra-small electromagnetic motor having an outer diameter of φ3 mm or less. A reflection surface that does not protrude from the dimensions is provided, and when the shaft rotates, the reflection surface is irradiated with light, and the transmitted light or reflected light is received to obtain a Z-phase signal. From the absolute origin can be grasped.
[0053]
In addition, the rotation direction switching function of the driver can grasp the rotation direction by actively performing forward / reverse rotation, and generate a pulse signal synchronized with the back electromotive voltage or coil current change of the driver's electromagnetic motor. Thus, even in an ultra-small electromagnetic motor, the rotation direction and the rotation speed can be detected.
[0054]
Also, by providing the encoder part rotating body so that it does not have a convex shape from the outer diameter of the output shaft, an additional protrusion such as a rotating body is provided compared to the conventional encoder system using a rotating disk or rotating drum. Therefore, an increase in the moment of inertia is eliminated, a decrease in response performance is avoided, and an increase in runout of the motor output shaft and an increase in bearing loss can be prevented.
[0055]
In addition, according to the micro servo motor unit of the present invention, it is not necessary to rotate a detection body having a large inertia on the output shaft having a very small diameter, and an undesirable phenomenon such as a repetitive motion of the output shaft is eliminated. Since there is no increase in the moment, it is possible to avoid a decrease in response performance and to prevent an increase in the amount of vibration of the motor output shaft and an increase in bearing loss.
[0056]
Further, according to the micro servo motor unit of the present invention, the number of FG pulses with respect to the movement of the servo motor output shaft (the output shaft of the speed reduction means) increases, so that the resolution can be improved and the controllability can be improved. It becomes possible.
[0057]
Further, according to the micro servo motor unit according to the present invention, the electromagnetic motor, the encoder, and the speed reduction means can be mounted on medical equipment such as an endoscope or a micro machine by setting the outer diameter to 3 mm or less.
[0058]
Further, according to the micro servo motor unit according to the present invention, an ultra-small encoder can be realized with a relatively simple component configuration even when the output shaft of the electromagnetic motor has an extremely small diameter such as φ0.3 mm.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a micro servo motor unit according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a first configuration example of an encoder according to an embodiment of the present invention.
3 is an explanatory diagram showing an example of the shape of an encoder output shaft in FIG. 2. FIG.
FIG. 4 is an explanatory diagram showing a second configuration example of the encoder according to the embodiment of the present invention.
FIG. 5 is an explanatory diagram showing a configuration example of a micro servo motor with a speed reduction mechanism according to an embodiment of the present invention.
FIG. 6 is a block diagram showing a system configuration of a conventional software servo.
FIG. 7 is a timing chart showing input / output signals of the pulse generator in FIG.
FIG. 8 is an explanatory diagram showing various examples of an incremental encoder.
[Explanation of symbols]
100 electromagnetic motor
110 Encoder
111 Motor shaft
111a Through hole
111b slit
111c Reflective surface
113 Light source
114 Light receiving sensor
120 drivers
121 Forward / reverse switching part
122 Motor back electromotive force FG pulse output section
140 Gearbox

Claims (2)

In a micro servo motor unit consisting of an ultra-compact micro motor consisting of an electromagnetic motor having an outer diameter of 3 mm or less, a speed reduction means and an optical encoder, and its driver,
Provided on the part of the shaft is a reflecting surface that reflects light in a state of not projecting from the outer diameter of the shaft on the side opposite to the output shaft of the electromagnetic motor , the speed reduction means that decelerates at a predetermined reduction ratio. When the output shaft rotates, the optical encoder that projects light on the reflecting surface, receives the reflected light, and outputs the Z phase in response to the light ON / OFF signal, and forward / reverse driving the electromagnetic motor. And a driver having a function of outputting a pulse signal synchronized with a change in counter electromotive voltage or coil current generated when the electromagnetic motor rotates. The optical encoder is provided on a side opposite to the output shaft of the electromagnetic motor, on a partial reflection surface formed in a state of not projecting from the outer diameter of the shaft, and on the same axis as the output shaft, and transmits light from a light source. an optical fiber for guiding the reflecting surface is projected light by the optical fiber, micro servo motor unit according to claim 1, characterized in that they are composed of a light receiving means for receiving light reflected by the reflecting surface.

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