JPH0136342B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to surface treatment of the magnetic core of a coil block or stator, which is a component of a step motor. FIG. 1 is a diagram showing an example of a conventional integrated stator type step motor, in which a coil block 3 has a coil wire 2 wound around a magnetic core 1 made of a high magnetic permeability material.
The two ends of the stator 4 are placed on top of the stator 4, which is also made of a high magnetic permeability material, and are screwed together to create a magnetic coupling.This allows the magnetic resistance distribution around the rotor 5 to be set correctly, and the coil block to The magnetic flux thus generated is guided around the rotor. However, if a material with poor corrosion resistance, such as pure iron or 45 permalloy, is used for the magnetic core 1 and stator 4, which are high magnetic permeability materials, rust will form on the surface and the overlapping portion of the magnetic core 1 and stator 4 will deteriorate. The magnetic resistance of the step motor increases, causing the magnetic resistance distribution around the rotor 5 to deviate from its original target value, and the magnetic flux generated by the coil block 3 also decreases, causing many problems such as a decrease in efficiency and magnetic resistance of the step motor. In addition, during long-term use, rust may fall off and enter the meshing parts, contacts, and bearings of gears, leading to serious functional defects. If non-magnetic plating is applied for the purpose of improving this corrosion resistance, the magnetic core 1
This is undesirable because a large amount of magnetic resistance is introduced between the magnet and the stator 4. For this reason, various attempts have been made to provide these with corrosion-resistant and magnetic plating, but conventional methods have had the following drawbacks. First, the use of electric nickel plating, which has magnetism, was considered, but the commonly used plating method has large variations in plating thickness, resulting in variations in corrosion resistance and step motor performance, which is unfavorable in terms of quality. Ta. Next, it was considered that after electroless plating with a non-magnetic nickel-phosphorus material, heat treatment was performed at around 400°C to impart magnetism to the plating film. With this method, there is little variation in thickness within a single plating process, but as the plating thickness increases, the performance of the step motor tends to be at the same level as non-magnetic plating. It was necessary to do it strictly. There is also the drawback that one additional heat treatment step is required. The present invention has been made to eliminate the above-mentioned drawbacks, and the surface of the magnetic core 1 or stator 4 is electrolessly plated with magnetic nickel-cobalt-phosphorus to reduce the magnetic resistance of the contact surface between the two. The purpose of this invention is to provide a highly efficient step motor. The present invention will be explained below with reference to the drawings. Figure 2 shows the current waveform flowing through the drive coil of the integrated stator step motor shown in Figure 1.
(a) is a current waveform when using a coil block with non-magnetic plating, (b) is a current waveform when using a coil block with nickel-cobalt-phosphorus electroless plating according to the present invention. are shown respectively. In the present invention, as shown in FIG. 2b, the rise time is longer (t ₂ >
_t1 ). In the integrated stator, when a current is passed through the coil, the magnetic flux first passes through the stator connecting portion 4a and becomes saturated, then passes through the rotor 5 area and contributes to the rotation of the rotor, and the pulse width is substantially reduced. The same effect occurs as (t ₀ ) becomes shorter. However, according to Ohm's law for magnetic circuits, that is, the relationship (number of coil turns), (current) = (magnetic resistance), (magnetic flux), the smaller the magnetic resistance, the more magnetic flux can be obtained by passing the same current. , magnetic core 2 and stator 4
In the present invention, where the magnetic resistance of the contact surface with the coil 1 is small, the magnetic flux generated by the coil 1 is larger than that of the conventional method, and the force exerted on the rotor 5 becomes stronger, resulting in a larger back electromotive force (i ₂ <i ₁ ). In other words, the pulse width is second to that of non-magnetic plating.
It can be seen that even though the rotor is substantially shorter than the one in Fig. a, the driving force of the rotor is not inferior and sufficient driving can be performed. Here, the rise times t ₁ and t ₂ occur when an integral stator is used, and are the times until the magnetic flux saturates the stator connecting portion 4a. This rise time is determined by the time constant (coil inductance/coil DC resistance), so it is proportional to the inductance, but the inductance is also (number of turns) ² /
(magnetic resistance) and is inversely proportional to magnetic resistance.
Therefore, according to the structure of the present invention having a small magnetic resistance, the rise time becomes longer as shown in FIG. 2b. It is clear from FIG. 2b that t ₀ is a pulse width sufficient to rotate the rotor. This is because the waveform rises sufficiently just before the pulse ends (indicating that the rotor magnetic poles have rotated to a position parallel to the coil magnetic field). The above explanation is about a one-piece stator type step motor, but it goes without saying that a two-piece stator type step motor, in which the left and right stators are separated, that is, the part shown in Fig. 1 4a is cut off, can have the same effect. . In fact, a watch with the same motor specifications (the stator is made of 78 permalloy and has a 45 permalloy magnetic core with glazing applied to it because there is no problem with corrosion resistance) was plated with nickel-cobalt-phosphorus electroless plating and the conventional method. Table 1 shows the performance of the step motor when applied.

[Table] As mentioned above, in the present invention, a magnetic film is applied to the surface of the magnetic core or stator by nickel-cobalt-phosphorus electroless plating, so the contact resistance of the screwed part is reduced, and the drive is equivalently improved. Even though the pulse width is shortened, the rotational force of the rotor is not impaired, a high efficiency step motor with low current consumption can be provided, and corrosion resistance can also be guaranteed. Further, since there is little variation in plating thickness and no heat treatment is required to impart magnetism, it is possible to easily provide a highly efficient step motor with uniform quality. Although this embodiment has been described with respect to a step motor for a watch, it is obvious that similar effects can be obtained with step motors having a similar structure other than those used in watches.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an example of a conventional step motor. FIGS. 2a and 2b are characteristic diagrams showing the waveform of the current flowing through the coil, where (a) is the one in which the magnetic core is plated with non-magnetic material, and (b) is the one according to the present invention. 1... Magnetic core, 2... Coil wire, 3... Coil block, 4... Stator, 5... Rotor.

Claims (1)

[Claims] 1. A step motor whose main components include a rotor made of a permanent magnet, a pair of stators made of a high magnetic permeability material arranged to surround the rotor, and a coil block having a magnetic core made of a high magnetic permeability material. On the magnetic core surface of the coil block, the surface of the stator, or both surfaces,
A step motor characterized by forming a nickel-cobalt-phosphorus magnetic film.