JPH1080127A - Stepping motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stepping motor which can reduce the torque loss by lessening the density of rotor material thereby lessening the inertial moment, and can prevent the occurrence of burrs at processing. SOLUTION: In a stepping motor, a cylindrical permanent magnet is used for a rotor 6, and N/S poles are magnetized in multipole alternately at the periphery, and the stator 7 is composed of two sets of electromagnets consisting of a yoke where pole teeth of the number corresponding to the number of the magnetized poles at the periphery of the rotor 6 and coils where coils wound into solenoids. The electromagnets are arranged so that the pole teeth may be slid by one-half pitch, thus a two-phase PM type of stepping motor is constituted. The outside diameter of the stepping motor is ϕ12 or under, and the diameter of the rotor is in the range of ϕ3.8-4.2, and the length of the rotor opposed to the pole tooth in the direction of the rotary shaft of the rotor is 2.6mm or over/phase, and the density (specific gravity) of the rotor material is 4.0 (g/cm<3> ) or under; this is such an anisotropic ferrite plastic magnet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a stepping motor used for driving a lens of a video camera or the like.

[0002]

2. Description of the Related Art An outline of the structure of a stepping motor used for driving a lens of a conventional video camera or the like will be described.

FIG. 7 is a general sectional view of a two-phase PM type stepping motor having an outer diameter of φ10. FIG. 2 is a diagram showing an example of use in a case where it is used as a drive source of a rear focus type zoom lens generally used in recent years for a lens of a video camera or the like. The motor shaft 1 is rotatably positioned by a tip bearing 3 lightly pressed into a motor holder 2 and a rear bearing 4 provided inside the case, or a motor holder and a motor case 8 (not shown).
Are positioned rotatably by a bearing lightly press-fitted into the motor holder and a tip bearing in the vicinity of the joint. The thrust spring 5 provides play in the thrust direction of the motor shaft and proper preload.

The cylindrical or stepped rotor 6 has an outer diameter of φ4.8 to φ5.0, is adhered and fixed to the motor shaft 1, and its outer peripheral surface is magnetized with 10 poles. Sm-Co or Nd-Fe as the rotor magnet material
-Maximum energy product is 7 with plastic magnet of B series.
The density (specific gravity) of the material is 5.5 to 6 MGOe.
In the range of 5, the surface magnetic flux is about ≒ 1 KG, and many are manufactured by compression molding.

The stator (stator) 7 has a number corresponding to the number of magnetized poles of the rotor, that is, has ten pole teeth, and forms a magnetic path with a motor holder and a motor case connected with screws (not shown). (In many cases, the opposing length of the pole teeth and the rotor in the direction of the rotation axis of the motor shaft is set to about 1.8 to 2.4 mm / phase), and two sets of coils 10 each having a bobbin 9 wound by a solenoid. It is composed of electromagnets. This electromagnet is arranged such that its pole teeth are shifted by a half pitch. That is, the rotor is rotated by energizing a rectangular wave or a sine wave having a phase shift of 90 ° in the coil.

A lens frame 12 is guided by a guide bar 11 fixed to a lens barrel (not shown) on the screw portion 1a of the motor shaft so as to be able to advance and retreat along the optical axis, and is mounted to the lens frame without play in the optical axis direction. The rack 13 and the like that can be equalized in the direction perpendicular to the optical axis can be engaged with each other and used for moving the lens forward and backward.

[0007]

The above-described conventional stepping motor has the following disadvantages. (1) φ1 used for driving lens for video camera
With a small-diameter stepping motor near zero, vibration and noise during operation of the stepping motor enter the microphone and cause a problem, so it is necessary to reduce the detent torque. Therefore, the rotor magnet material (Sm-Co-based or Ne-B-based plastic magnet) accounts for 50% to 70% of full magnetization.
%. It is possible to use a pole tooth and a rotor whose opposing length in the direction of the rotation axis of the motor shaft is about 3 mm / 1 phase, but actually, 1.8 to 2.
Many are set to about 4 mm / phase. Also,
The rotor system is set relatively large with respect to the motor outer diameter,
Since the density (specific gravity) is large, the moment of inertia is large, the torque loss is large, and the performance of the magnet is not sufficiently utilized. Therefore, the cost is high. (2) Since compression molded products are generally used for magnets, if a step is provided at the center of the rotor, secondary processing is required, which increases the cost. Also, burrs (magnetic powder) due to secondary processing (lathe) are required. As a result, the gap between the rotor and the pole teeth is clogged, and malfunction occurs.

[0008]

According to the present invention, first, a cylindrical permanent magnet is used for a rotor (rotor), and N / S poles are alternately multipole-magnetized on an outer peripheral surface of a stator (rotor). The stator is composed of two sets of electromagnets including a yoke having a number of pole teeth corresponding to the number of magnetized poles on the outer peripheral surface of the rotor and a coil wound by a solenoid. This electromagnet has two pole teeth
In two sets of PM stepping motors which are arranged so as to be shifted by one-one pitch, the outer diameter of the stepping motor is not more than φ12, the rotor diameter is in the range of φ3.8 to 4.2, and the rotation axis of the rotor is The length of the rotor facing the pole teeth in the direction is 2.6 mm or more / phase, and the density (specific gravity) of the rotor material is 4.0 g / cm ³ or less. Therefore, an inexpensive stepping motor can be provided.

According to the present invention, secondly, the density (specific gravity) of the rotor material in the stepping motor having the above-described configuration is 4.0.
Since an anisotropic ferrite plastic of [g / cm ³ ] or less is used as a material suitable for injection molding, the degree of freedom of the shape is high and secondary processing or the like is not required, thereby preventing generation of burrs and the like.

[0010]

【Example】

(Embodiment 1) FIG. 1 is a sectional view of a φ10 stepping motor according to Embodiment 1 of the present invention. The motor shaft 1 is rotatably positioned by a front bearing 3 lightly pressed into a motor holder 2 and a rear bearing 4 provided inside the case. The thrust spring 5 provides play in the thrust direction of the motor shaft and proper preload.

The rotor 6 is bonded and fixed to the motor shaft 1, and its outer peripheral surface is magnetized with 10 poles. In this embodiment, the motor shaft of a stepping motor used for driving a lens of a video camera or the like is generally a rolled screw, and φ2 is used from the viewpoint of accuracy assurance.
The outer diameter of the rotor was set to φ4 because the coil winding space was increased by about 50% as compared with the conventional example, and the air gap between the pole teeth and the rotor was brought close to the range in which production was possible.

The rotor magnet is made of an anisotropic ferrite plastic magnet and has a maximum energy product of 2.2M.
GOe, density (specific gravity) of the material is 3.8 [g / cm ³ ]
Thus, a surface magnetic flux of 500 to 600 G can be easily obtained, and it can be used in a state close to almost full magnetization.

The stator (stator) 7 has a number corresponding to the number of magnetized poles of the rotor, ie, ten pole teeth, and forms a magnetic path with a motor holder and a motor case connected with screws (not shown). (The opposing length of the pole teeth and the rotor in the direction of the rotation axis of the motor shaft is set to 2.8 mm / phase. The opposing length of the rotor can be used as a cylinder as long as the opposing length is not problematic.) Wound coil 1
It is composed of two sets of electromagnets consisting of zero. The electromagnet is arranged such that its pole teeth are shifted by a half pitch. That is, the rotor is configured to rotate by energizing a rectangular wave or a sine wave having a phase shift of 90 ° in the coil.

A lens frame 12 is guided by a guide cover 11 fixed to a lens barrel (not shown) on the screw portion 1a of the motor shaft shown in FIG. 2 so as to be able to advance and retreat along the optical axis. A rack 13 or the like, which is mounted without being mounted and can be equalized in a direction perpendicular to the optical axis, can be used for moving the lens forward and backward.

FIG. 3 shows the calculation of the inertia including the motor shaft and the rotor of the stepping motor of the conventional example and the first embodiment, which is necessary for accelerating the stepping motor alone under no load corresponding to the pulse rate (two-phase drive display) PPS. FIG. 6 shows characteristics obtained by comparing various torques, and FIG. 6 shows abbreviations of dimensional relationships. The characteristic table of FIG. 3 is a value calculated based on the dimensions described in Table 1 of the attached sheet.

As can be seen from the characteristic graph of FIG. 3, it can be seen that the rotor of the first embodiment has a clearly reduced inertia as the drive pulse rate increases. This is the effect that the moment of inertia of the rotating body is proportional to the fourth power of the diameter and the effect that the density (specific gravity) of the rotor is obtained by a 40% reduction effect. As a result, the required acceleration torque is the square of the driving pulse rate. The effect increases as the pulse rate becomes higher in proportion to. That is, the characteristics can be improved by making the diameter of the rotor as small as possible and selecting a material having a small density (specific gravity).

FIG. 4 shows calculated values of the motor shaft (output shaft) torque and pulse rate of the stepping motor of the conventional example and the first embodiment. The parameters related to the torque generated by the stepping motors of the conventional example and the first embodiment are shown in Table 2 on the separate sheet except for the motor shaft and rotor dimensions described above.

General conditions when used for driving a lens of a video camera or the like will be described. As for the drive input, the input voltage to the coil is a sine wave input of 4 V ^PEAK / each phase (coil resistance is 50 Ω) due to the demand for low power consumption and low noise.
/ Each phase). The use range of the pulse rate is used up to around $ 480PPS,
Since the driving load is used for forward and backward movement by the rack as shown in FIG. 2, the load torque is about 1 gcm.
The output shaft torque near 0 PPS is generally set to about 2 gcm, which is almost twice as large. For this reason, temporarily 480PP
In S, based on the output shaft torque of 2 gcm as a reference, the output shaft torque when the input current to the coil is assumed to be constant irrespective of the pulse rate is calculated from the acceleration torque value required for the stepping motor alone in FIG. In comparison with the characteristics of the stepping motor of the first embodiment, the pulse rate region in which 2 gcm can be guaranteed is clearly expanded as is clear from the characteristic graph of FIG. This is lower than that of the conventional example at a low pulse rate, but the required torque is 2 gcm, which is enough to suppress deterioration such as vibration due to high torque. Above 360 PPS in the high pulse rate region, the rotor becomes lighter and has a lower inertia, so that the higher the speed is, the more advantageous it becomes.

FIG. 5 is a graph showing the results of actually measuring the relationship between the output shaft torque and the pulse rate of the stepping motor of the conventional example and the first embodiment. In taking the data, the input current to the coil of the stepping motor was set as a sine wave and set at $ ⁶⁰ mA ^PEAK / phase. Other settings are the same as those described above. Although the absolute value of the generated torque is slightly lower, it is easy to improve the absolute value of the generated torque by reducing the gap between the rotor and the pole teeth or increasing the facing length between the rotor and the pole teeth. This is a sufficient result to prove the effectiveness of this proposal.

[0020]

As described above, according to the present invention,
A cylindrical permanent magnet is used for the rotor (rotor), and N / S poles are alternately multipolar magnetized on the outer peripheral surface, and the stator (stator) has a number corresponding to the number of magnetized poles on the outer peripheral surface of the rotor. It consists of two sets of electromagnets consisting of a yoke with pole teeth formed and coils wound by solenoids. This electromagnet is a two-phase PM arranged so that its pole teeth are shifted by a half pitch.
In the stepping motor, the outer diameter of the stepping motor is 12 or less, the rotor diameter is in the range of 3.8 to 4.2, and the length of the rotor facing the pole teeth in the rotation axis direction of the rotor is 2.6 mm or more / phase. Since the rotor material has a density (specific gravity) of 4.0 g / cm ³ or less, it is possible to provide an inexpensive stepping motor.

The density (specific gravity) of the rotor material in the stepping motor having the above-described configuration is 4.0 g / c.
m ³ ] or less is used as a material suitable for injection molding, so that an inexpensive and high-quality stepping motor can be provided.

[Table 1]

[Table 2]

[Brief description of the drawings]

FIG. 1 is a sectional view of a stepping motor according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of use of a stepping motor.

FIG. 3 is a characteristic graph comparing a relationship between a required acceleration torque and a pulse rate under no load including a motor shaft and a rotor of the stepping motor of the conventional example and the stepping motor of the first embodiment.

FIG. 4 is a characteristic graph showing a calculation comparison of the output shaft (motor shaft) torque-pulse rate between the conventional example and the stepping motor according to the first embodiment.

FIG. 5 is a characteristic graph showing actual measured values of the output shaft torque of the conventional example and the stepping motor of the first embodiment.

FIG. 6 is a diagram illustrating a dimensional relationship (abbreviated symbol) between a motor shaft and a rotor.

FIG. 7 is a sectional view of a conventional stepping motor.

[Explanation of symbols]

 Reference Signs List 1 motor shaft 2 motor holder 3 tip bearing 4 rear bearing 5 thrust spring 6 rotor 7 stator 8 rotor case 9 bobbin 10 coil 11 guide bar 12 lens frame 13 rack

Claims (2)

[Claims] 1. A cylindrical permanent magnet is used for a rotor (rotor), and N / S poles are alternately multipolar magnetized on an outer peripheral surface, and a stator (stator) has the number of magnetized poles on the outer peripheral surface of the rotor. And two sets of electromagnets each composed of a yoke having a number of pole teeth corresponding to the number of teeth and a coil wound by a solenoid, and the electromagnets are arranged so that the pole teeth are shifted by a half pitch. In the PM type stepping motor, the outer diameter of the stepping motor is φ12 or less, and the rotor diameter is φ3.8 or more.
4.2, the length of the rotor facing the pole teeth in the rotation axis direction of the rotor is 2.6 mm or more / phase, and the density (specific gravity) of the rotor material is 4.0 [g / cm ³ ]. A stepping motor comprising the following anisotropic ferrite plastic magnet. 2. The stepping motor according to claim 1, wherein the density (specific gravity) of the rotor material is 4.0 g / c.
m ³ ] The following anisotropic ferrite plastic is a material that can be injection-molded.