JPS6226251B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voice coil type linear motor.

Generally, voice coil type linear motors are used in various devices and equipment, but among them, voice coil type linear motors are used as servo motors, and servo tracks are set on a specific disk surface within a magnetic disk, that is, on a servo disk surface. Then, a magnetic head, ie, a servo head, reads position information recorded in advance on the servo track, and performs positioning as a position servo signal. So-called track following type magnetic head positioning devices are mainstream.

In order to obtain high positioning accuracy in such a track-following type magnetic head positioning device, it is necessary to configure the positioning system so that the servo head sufficiently follows the vibrations of the servo track, thereby minimizing the following error. This is absolutely necessary and results in increasing the loop gain of the positioning servo system.

On the other hand, increasing the loop gain reduces the attenuation characteristics of the system, and in some cases may result in oscillation of the system. Therefore, in the magnetic head positioning device, by feeding back the speed signal as a damping signal in addition to the position signal, it is possible to achieve sufficient followability while ensuring appropriate damping characteristics, that is, stability of the positioning system. It is normal that

Conventionally, the method for obtaining the speed signal is to add a linear tachogenerator to generate the speed signal, or to differentiate the position signal to form a speed signal, and to feed back the voice as a damping signal. Currently, damping force is generated in a coil type linear motor.

However, in the former case, it is obvious that a linear tachogenerator must be provided, and furthermore, an electronic circuit for amplifying the output of the tachogenerator is also necessarily required. Furthermore, the latter method also requires a differentiating circuit for differentiating the position signal, which has the drawback of increasing the complexity and number of electronic circuits, which in turn increases the cost.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks, and to generate damping force with a relatively simple configuration and inexpensive means without requiring a linear tachogenerator or a differentiating circuit. At the same time, it is an object of the present invention to provide an improved voice coil type linear motor equipped with a novel means that allows the damping force to be set and controlled arbitrarily to a desired value even during positioning operation.

According to the present invention, a permanent magnet, a front yoke,
It is composed of a back yoke, a center pole, a voice coil, a movable rod, a movable rod slider, a carriage, etc., and one end surface of the voice coil, which is made by winding a single conductor into a cylindrical shape, is fixed to the carriage, and the center pole and The center of the voice coil is aligned with the center pole, and an appropriate minute gap is maintained between the inner surface of the voice coil and the outer peripheral surface of the center pole, and the effective magnetic flux formed by the permanent magnet, front yoke, back yoke, and center pole is The gap and the conductive wire of the voice coil are constructed so as to be perpendicular to each other, and the voice coil is caused to move linearly by an electric current supplied from the outside, and the direction of the linear movement is determined by the polarity of the electric current. In a conventional voice coil type linear motor, the movable rod having a circular cross section is arranged perpendicular to the voice coil mounting surface of the carriage, and the voice coil is aligned with the center of both cross sections of the movable rod. fixed to the coil mounting surface, and further provided with a center hole in the center of the center pole parallel to the direction of motion of the voice coil, and an inner surface of the center hole and an end opposite to the end fixed to the carriage of the movable rod. The gap formed by the outer circumferential surface of the movable rod slider added to the rod slider is configured to be arbitrarily variable, and at the same time, the center hole is configured to be filled with air or a viscous fluid such as oil.

Therefore, when a driving current is applied to the voice coil from the outside, the movable rod and the movable rod slider are integrated through the voice coil and the carriage, so that they perform linear motion within the center hole. At this time, the viscous fluid sealed in the center hole passes through the gap formed between the inner surface of the center hole and the outer peripheral surface of the movable rod slider, and flows in a direction opposite to the direction of movement of the movable rod slider. Due to the flow of the viscous fluid, the movable rod slider is subjected to a viscous force in a direction opposite to the direction of the linear motion and proportional to the velocity.

Further, since the viscous force changes depending on the length of the gap, an optimum damping force can be easily generated by changing the length of the gap even during positioning operation. That is, the cross-sectional area, radius, and length of the movable rod slider are A (cm ² ), r (cm), and l (cm), respectively, and the gap formed by the inner surface of the center hole and the outer peripheral surface of the movable rod slider. The length is ε (cm), the viscosity coefficient of the viscous fluid sealed in the center hole is μ (Kg cm ^-2 sec), the viscous force is (Kg), and the displacement of the linear motion of the movable rod slider. ^{If x} (cm) ^and 2] Also, x=dx/dt.

From equations [1] and [2], by appropriately selecting the cross-sectional area A, radius R, length l, and gap length ε of the movable rod slider, as well as the viscosity coefficient μ, the desired viscous force, that is, the desired damping can be obtained. The viscous damping constant C can generate a force, and at the same time, as is clear from equation [2], by changing the gap length ε, an optimum damping force is generated for the positioning servo system.
can be set even during positioning operation.

Therefore, there is no need for a linear tachogenerator or a speed detection differentiation circuit that differentiates the position signal, and even during positioning operation, it is possible to arbitrarily generate damping force that is optimal for the positioning servo system. This can also be achieved by relatively simple and inexpensive means.

Therefore, the object of the present invention can be fully achieved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Details of embodiments of the present invention will be described below with reference to the drawings.

Figures 1 and 2 are diagrams showing an embodiment of the present invention. Figure 1 shows only the magnet part of a voice coil type linear motor, omitting the movable parts, such as the voice coil, carriage, movable rod, and movable rod slider. The perspective view and FIG. 2 are side views including a partial cross section.

Referring to Figures 1 and 2, 1A, 1B
is a permanent magnet, 2 is a front yoke, 3 is a back yoke, 4A is a center pole, 4B is a center hole, 4
C is the center hole, viscous fluid sealed in 4B, G is an effective magnetic flux gap, 5 is a movable rod, 6
is a movable rod slider equipped with a gap adjustment mechanism,
7 is a gap formed by the inner surface of the center hole 4B and the outer peripheral surface of the movable rod slider 5B;
8 is a voice coil, 9A is a carriage, 9B is a voice coil mounting surface of the carriage 9A, 10 is an O-ring, 11 is an O-ring support plate, 12 is an O-ring stop plate, 13 is a packing, 14 is a backing plate, 15A,
15B is a screw, D1 and D2 are arrows indicating the direction of motion of the voice coil 6 and movable rod 5, representing the front and rear, respectively, and the permanent magnets 1A and 1B are facing each other with respect to the center pole 4A, and each is facing the front. A center pole 4A, which is sandwiched and fixed between both sides of the yoke 2 and the back yoke 3 and has a circular cross section, is press-fitted into the center of the back yoke 3 perpendicularly. Therefore, the permanent magnet 1
A, 1B, the front yoke 2, the back yoke 3, and the center pole 4A form a magnetic circuit, and this magnetic circuit has an effective magnetic flux gap G with a minute gap between the front yoke 2 and the center pole 4A. form. On the other hand, the voice coil 8 and the movable rod 5 each have their cross-sectional centers coincident with each other on one end surface thereof, and are fixed perpendicularly to the voice coil mounting surface 9B of the carriage 9A. The inner surface, the outer circumferential surface of the center pole 4A, the outer circumferential surface of the voice coil 8, and the inner surface of the front yoke 2 maintain appropriate gaps, respectively, and at the same time, the magnetic flux in the effective magnetic flux gap G and the conductive wire of the voice coil 8 are maintained. The movable rod 5 is fixed to the voice coil mounting surface 9B and the inner surface of a center hole 4B that is arranged orthogonally to each other and that extends through the center of the center pole 4A in parallel to the motion directions D1 and D2 of the voice coil 8. A gap 7 is formed between the end and the outer peripheral surface of the movable rod slider 5 installed at the opposite end, and the back yoke 3 side of the center hole 4B is connected to a backing plate 14 via a packing 13. It is screwed to the back yoke 3 by a screw 15B and two screws not shown.
Further, the O-ring 10 is supported by an O-ring support plate 11 and an O-ring stopper plate 12, and is further screwed to the center pole 4A with a screw 15A and three screws not shown. The outer peripheral surface can freely move linearly in the directions of the arrows D1 and D2 while contacting the O-ring 10, and both sides of the front yoke 2 and the back yoke 3 of the center hole 4B are in contact with the O-ring 10. The hole is sealed by the packing 13 so that the viscous fluid 4C sealed in the center hole 4B does not leak to the outside.

Now, when a drive current is applied to the voice coil 8 and a linear movement occurs in the direction of the arrow D2, the voice The linear motion is performed together with the coil 8. At this time, the viscous fluid 4C sealed in the center hole 4B flows through the gap 7 in a direction opposite to the direction of movement, that is, in the direction of arrow D1.

Therefore, the movable rod slider 6 is moved as indicated by the arrow D1.
In the direction of , it is subjected to a viscous force proportional to the speed of the linear motion, that is, a damping force expressed by equations [1] and [2].

Furthermore, as is clear from equations [1] and [2], obtaining the desired viscous force comes down to determining the viscous damping constant C. That is, since the viscosity coefficient μ is naturally determined by the viscous fluid 4C used, the viscous damping constant C is determined by the cross-sectional area A, the length l, and the gap length ε of the movable rod slider 6. Therefore, by changing the gap length ε, it is possible to obtain the viscous damping constant C such that a desired viscous force is generated. That is, by means of a gap adjustment mechanism for adjusting the gap length ε of the gap 7 provided in the movable rod slider 6, the viscous damping constant C is set even during the positioning operation so as to provide an optimum damping force to the positioning servo system. be able to.

Figures 3 and 4 show an embodiment of the movable rod slider 6 having a gap adjustment mechanism used in the voice coil type linear motor of the present invention, and show the non-operating state and the operating state of the gap adjustment mechanism, respectively.
is a side view, and b is a front view. Note that the viewpoints in Figures 3 and 4 differ by 90 degrees.

5 and 6 are exploded views of the movable rod slider 6 shown in FIGS. 3 and 4, in which a is a side view and b is a front view.

Referring to FIGS. 3, 4, 5, and 6, 5 is a movable rod, 6A is a first movable rod slider, and 6B is the first movable rod slider 6.
6C is a second movable rod slider, 6D is a dovetail groove formed in the second movable rod slider, 16A and 16B are piezoelectric elements and leaf springs, respectively; 1,
A second drive element, 18 is a joining member, and 6E is a drive element storage part for accommodating the first and second drive elements 16 and 17, which connects the movable rod 5 and the first drive element.
The movable rod slider 6A is not shown in the figure, but each has a male thread and a female thread, and is connected to the first movable rod slider 6A and the two second movable rod sliders 6C. The driving element housing portions 6E face each other and are engaged with the dovetail groove engaging portions 6B and the dovetail grooves 6D to form a single body, and furthermore, from the left and right (up and down in FIG. 4), the dovetail grooves The engaging portion 6B and the dovetail groove 6D are assembled so as to be movable while engaging with each other. On the other hand, the drive element 16A and the leaf spring 16B are glued together with adhesive, and the first,
A second drive element is formed, and a connecting member 18 connects the plate springs 16B of the first and second drive elements.
The center portions of the two are joined together to form a driving section.

In the present invention, stainless steel for springs is used as the leaf spring 16B and the joining member 18, and after spot welding the two leaf springs 16B to the joining member 18 at their centers in advance, the joining member 18 of the leaf spring 16B is A piezoelectric element 16A, ie, PZT, having the same size as the leaf spring 16B is bonded to the non-welded surface with adhesive.

Further, the driving section including the first and second driving elements is fixed to the driving element storage section 6E so that the first and second driving elements are supported at both ends.

Therefore, the two second movable rod sliders 6C, in which the drive element housing portions 6E are assembled to face each other, operate as shown in FIG. 3 until voltage is applied to the first and second drive elements. As shown in FIG.
It is pulled back by the spring force of B.

When a voltage is applied to the piezoelectric element 16A through a conducting wire (not shown), the piezoelectric element 16A is displaced as shown in FIG. The piezoelectric element 16A moves in the direction by a length equal to the displacement, and the force generated in the piezoelectric element 16A and the spring force of the plate spring 16B are balanced and the piezoelectric element 16B comes to rest.

Further, in general, a fixed relationship exists between the displacement δ (cm) of the piezoelectric element 16A in the direction of the arrow 19 and the applied voltage E (Volt), that is, a proportional relationship as shown in the following equation [3].

δ=KE ...... [3] However, K is the electrostriction constant, Young's modulus, mechanical dimensions (width, length, thickness) of the piezoelectric element, the Young's modulus of the leaf spring, mechanical dimensions, and the support of the drive element. It is a constant determined by the method, ie, cantilever, support at both ends, etc.

Referring to FIG. 4, since the movable rod slider 6 changes from a circular shape to an elliptical shape due to the displacement δ, the length of the gap formed between the outer peripheral surface of the movable rod slider 6 and the inner surface of the center hole 4B is Although it is not possible to change the displacement equally over the entire circumference of the movable rod slider 6, the displacement δ is approximately several hundred microns, which is extremely small compared to the radius of the movable rod slider 6, and in practical terms, the displacement δ cannot be changed equally over the entire circumference. It may be assumed that the change is an equal gap.

Therefore, from equation [3], the displacement δ, that is, the gap length ε, is controlled by the applied voltage to the piezoelectric element 16A, and the viscous damping constant C shown in equation [2], that is, shown in equation [1], is controlled. The viscous force can be set and controlled arbitrarily to a desired value.

Therefore, in the magnetic head positioning device used as a conventional voice coil type linear motor, the speed to generate the damping force that is absolutely necessary to obtain sufficient tracking accuracy while ensuring appropriate stability of the control system is required. It is possible to generate a damping force with a relatively simple and inexpensive means without having a detector, that is, a linear tachogenerator or a differentiation circuit for differentiating a position signal. Among them, it is possible to set and control the desired value arbitrarily.

Therefore, the object of the present invention can be fully achieved.

Although the operating principle of the present embodiment has been described in detail above, modifications can be made without departing from the spirit of the present invention, and the above description does not limit the scope of the present invention.

[Brief explanation of the drawing]

1 and 2 are a perspective view and a partially cutaway side view showing an embodiment of the present invention, FIG. 1 is a perspective view showing a magnet part of a voice coil type linear motor, and FIG. 2 is a partially cutaway side view. 3 and 4 are side views including a cross section, and FIGS. 3 and 4 show an embodiment of a movable rod slider having a gap adjustment mechanism used in the voice coil type linear motor of the present invention; a is a side view; b is a partial view; FIG. 5 and 6 are exploded views of the movable rod slider shown in FIGS. 3, 4, and FIG. 4 is a side view, and b is a front view. 1A and 1B are permanent magnets, 2 and 3 are a front yoke and a back yoke, respectively, 4A and 4B are a center pole and a center hole, respectively, 5 is a movable rod 6 is a movable rod slider, 7 is a gap, 8 is a voice coil, 9A and 9B are 10 is an O-ring, 11 is an O-ring support plate, 12 is an O-ring retaining plate, 13 is a packing,
14 is a patch plate, 15A, 15B are screws, 16, 1
7 is a drive part, 18 is a joining member, 19, D1, D2
is an arrow indicating the direction of motion, G is the effective magnetic flux gap,
δ is displacement.

Claims (1)

[Claims] 1 Permanent magnet, front yoke, back yoke,
The permanent magnet is sandwiched between the front yoke and the back yoke, and one end of the center pole is fixed to the back yoke, and the front An effective magnetic flux gap is formed by the yoke and the outer periphery of the other end of the center pole that is not fixed to the back yoke, and one end surface of the voice coil is fixed to the carriage, and the center pole and the voice coil, the centers of which coincide, the inner surface of the voice coil and the outer peripheral surface of the center pole maintain a minute gap, and the effective magnetic flux gap and the conductor of the voice coil are perpendicular to each other. In the type linear motor, the movable rod is fixed to the voice coil mounting surface perpendicular to the voice coil mounting surface of the carriage so that the centers of both cross sections of the voice coil and the movable rod coincide, and the center pole a first movable rod slider having a center hole provided in the center thereof parallel to the direction of motion of the voice coil and having a dovetail groove engagement portion;
A second movable rod slider having a dovetail groove that engages with the dovetail groove, and a drive element that is fixed to the second movable rod slider so as to be supported at both ends and moves the two second movable rod sliders. A gap is formed between the movable rod slider, the inner surface of the center hole, and the outer peripheral surface of the movable rod slider attached to the end opposite to the end fixed to the carriage of the movable rod, and the The gap is configured to be arbitrarily variable by driving the movable element to drive the two second movable rod sliders in the radial direction, and at the same time, a viscous fluid is sealed in the center hole. Voice coil type linear motor.