JP2948010B2 - Linear driving apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a linear drive that combines hydrostatic gas bearings and voice coil type motor.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional linear drive device used for a precision measuring instrument or the like. A voice coil motor composed of a coil assembly 103a and a magnetic circuit assembly 103 is disposed at one end of a shaft 102 having a rectangular cross section supported by a hydrostatic gas bearing 101, and a linear encoder 104 is mounted at the other end. And a measuring machine or the like is attached to the shaft end 102a. The voice coil motor 103 sends the shaft 102 to a target position based on the position signal of the linear encoder 104.

As disclosed in Japanese Utility Model Laid-Open Publication No. 59-72317, in a shaft and a bearing having a circular cross section, in order to restrict the rotational freedom of the shaft, an anti-rotation member is provided between the shaft and the bearing. In some cases, a joint portion and an engagement portion thereof are provided with a fluid outlet.

[0004]

However, in the above conventional example, in the case of the configuration shown in FIG. 7 , since the voice coil motor and the static pressure gas bearing are arranged in series, the apparatus becomes large, and the shaft cross section has a rectangular shape. In order to form the hydrostatic gas bearing, the number of parts is increased, and adjustment work such as gap adjustment is required at the time of assembling, and the cost is high. In addition, 5
In the configuration described in Japanese Patent Application Laid-Open No. 9-72317, an engagement portion for preventing rotation is provided between the shaft and the bearing, and a mating member that engages with the engagement portion is an air outflow passage provided on the inner wall of the elongated hole or the inner wall of the bearing. Therefore, it is difficult to process them with high precision, and it is difficult to adjust the gap, and the productivity is low.

In the above conventional example, when the supply of the pressurized gas is stopped due to a malfunction of the apparatus or a human error, the shaft comes into contact with the bearing, and when an external force or the like acts on the apparatus, the shaft is Moved in a contact state, and sometimes damaged the shaft and the bearing.

Further, in the closed space surrounded by the coil of the voice coil motor, the only part that communicates with the outside (atmosphere) is only the gap between the coil and the yoke, and the exhaust efficiency is poor. Due to the pressure change accompanying the change, the coil and the shaft are about to be displaced in the axial direction (positioning direction) (displacement on the order of 0.1 μm), which excites vibration in the axial direction and causes deterioration of positioning accuracy and positioning time. There was a disadvantage that it becomes.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, and a first object of the present invention is to provide a highly productive straight line having a small size and a simple structure, which facilitates assembling work and gap adjustment. A drive device is provided. A second object is to provide a linear drive device in which the shaft and the bearing of the hydrostatic gas bearing are prevented from being moved by an external force in a state where the shaft and the bearing are in contact with each other when the supply of the pressurized gas is stopped. A third object is to improve the efficiency of exhausting from a closed space surrounded by the coil of the voice coil motor in the linear drive device.

[0008]

To achieve [Means for solving and acting object, wherein the first object, according to the present invention, integrally arranged voice <br/> scan coil motor and the bearing is the main mechanism, the main mechanism Other than the mechanism between the shaft and the bearing (outside the bearing housing)
By disposing the and so excluding the disadvantages in terms of cost and productivity of the prior art. As a mechanism other than the main mechanism
Is a detent mechanism that restricts the degree of freedom of rotation of the shaft.
A lock mechanism and the like can be exemplified. The detent
The mechanism consists of a flat hydrostatic gas bearing and a flat guide.
Can be made into a simple shape, miniaturizing the entire device
Help.

In order to achieve the second object, according to the present invention, a mechanism for locking a movable body (shaft) is provided to eliminate the disadvantage of the conventional example that the shaft and the bearing are damaged. I am . That is, in the present invention, a linear drive device that positions a shaft in a predetermined direction by a static pressure gas bearing and a voice coil motor, wherein the static pressure gas bearing and the shaft supported by the static pressure gas bearing In a linear drive device disposed inside the magnetic circuit assembly, a lock mechanism for restricting the degree of freedom in the movement direction of the shaft is provided.

In order to achieve the third object, according to the present invention, in a linear drive device for positioning an axis at a predetermined position by a static pressure gas bearing and a voice coil motor, the linear drive device is surrounded by a coil of the voice coil motor. An exhaust hole communicating from the closed space to the outside is provided to improve the efficiency of exhaust from the closed space.

[0011]

FIG. 1 is a partial sectional view of an embodiment of the present invention.
FIG. 2 is a view taken in the direction of the arrow X in FIG. 1 is a cylindrical bearing housing. Reference numerals 2a and 2b denote annular porous bearing members fitted to the bearing housing 1 by shrink fitting or the like, and have exhaust grooves 3 provided in the circumferential direction. Reference numeral 4 denotes a plurality of air supply grooves provided in the circumferential direction of the bearing housing as shown in the figure. 5 is a shaft, and 6 is a minute gap. Reference numeral 7 denotes an air supply hole provided in the bearing housing 1 and communicates with the air supply groove 4 as shown in the figure. Reference numeral 8 denotes an exhaust groove provided on the outer peripheral surface of the bearing housing 1, and an exhaust hole 9 communicates therewith. A is a magnetic circuit assembly of the voice coil motor, which is composed of a yoke member 10 and a magnet 11. 10a
Denotes an outer yoke member, and 10b denotes an inner yoke member. The magnetic circuit assembly A is provided with, for example, a mounting member 12, and the mounting member 12 is fixed to the base 14 with bolts 13 or the like. The bearing housing 1 is fitted to the inner diameter portion of the magnetic circuit assembly A, and is fixed by bolts 15. B is a coil assembly of the voice coil motor, which is composed of a coil head 16, a sleeve and a coil 17. The voice coil motor C includes a magnetic circuit assembly A and a coil assembly B. Reference numeral 18 denotes an exhaust hole provided in the coil head 16. The coil head 16 is fixed to one end of the shaft 5. A head member 19 is attached to the other end of the shaft 5. Reference numeral 19a is a mounting surface for a measuring instrument (not shown). D is a linear encoder, which includes a detection head 20 and a scale 21. The detection head 20 is attached to the base 1 by the mounting member 22.
Fixed to 4. The scale 21 is fixed to the scale mounting portion 19b of the head member 19 by a leaf spring member (not shown) or the like. 23 is a light shielding member.

E is a rotation preventing unit, and FIG. 3 is a partial sectional view thereof. Detent unit E is a holding member 27 for holding the plate-shaped porous bearing members 26a and 26b in which the both sides thereof guide Plate 24 fixed arranged with a predetermined small gap 25 in the head member 19 Be composed. 28 is a pocket provided on the holding member 27,
29 is an air supply hole.

FIG. 4 is a view taken in the direction of the arrow Y in FIG.
3 shows the mounting part of. Reference numeral 30 denotes an air cylinder (for example, a single-acting extrusion type), which is fixed to the bearing housing 1 by a bracket 31. 32 is a clamp head provided on the rod of the air cylinder 30, and 33 is a clamp table. 34 is a leaf spring fixed to the head member 19,
As shown in the figure, a predetermined gap is provided between the clamp head 32 and the clamp table 33.

In the above structure, when pressurized gas is supplied from the air supply hole 7 of the bearing housing 1, the gas passes through the annular porous bearing members 2a and 2b, is ejected to the minute gap 6, and the shaft 5 can be moved in the axial direction. To support static pressure. The pressurized gas ejected into the minute gap 6 is directly discharged to the outside from the bearing end on the head member 19 side, and passes from the bearing housing 1 through the other bearing end, the exhaust hole 9 and the exhaust groove 8 to the coil. The yoke member 10a and the gap h between the magnet 11 and the sleeve 17 are discharged to a closed space V surrounded by the assembly B.
₁ and h ₂ and the exhaust hole 18 are discharged to the outside of the apparatus.

On the other hand, in the detent unit E, when pressurized gas is supplied from the air supply hole 29 of the holding member 27, it passes through the flat porous bearing members 26a and 26b and passes through the minute gap 25.
The nozzle guide plate 24 is statically supported to restrict the rotational freedom of the shaft 5. The pressurized gas ejected into the minute gap 25 is discharged from the bearing end to the outside. Voice coil motor C
Moves the shaft 5 to a predetermined position based on the position signal from the linear encoder D. The air cylinder 30 normally (when the pressurized gas is supplied and the apparatus is in an operating state) protrudes the clamp head 32 to a position as shown in the figure, but the pressurized gas is caused by a malfunction of the apparatus or a human error. Is no longer supplied, the clamp head 32 is retracted to clamp the plate 34 and restrain the shaft 5 from moving in the axial direction.

Next, the diameter d of the exhaust hole 18 will be described. Assuming that the number of the exhaust holes 18 is n, the conductance C ₂ of the exhaust holes 18 is expressed by the following equation (1).

[0017]

(Equation 1) If the conductance of the gaps h ₁ and h ₂ between the yoke member 10 a and the magnet 11 and the sleeve 17 is C ₁ , the total conductance C ₀ is C ₀ = C ₁
+ C ₂ .

Gas is discharged from the bearing housing 1 to the closed space V, but when the coil assembly B and the shaft 5 are stopped (when positioning is completed, etc.), the pressure in the closed space V and the external (atmospheric) pressure are reduced. The pressures are balanced and there is no disturbance to axial positioning. A flow rate Q corresponding to a volume change ΔV per unit time of the closed space V when the shaft 5 is moved to some extent by the voice coil motor C.
But coil set for the three-dimensional B is discharged from the gap h _1, h ₂ and an exhaust hole 18 at the moment when moved, the pressure in the closed space V is, atmospheric pressure P if _{a ΔP} = P _a · Q / C ₀
Needs to be changed by the amount ΔP represented by If the length of the closed space V in the axial direction is L, the coil assembly B is ΔΔ
about to be moved by an amount Δx represented by _{x = ΔP · L / P a} . This causes axial vibration. Therefore, if x ₀ is a design allowable value of the vibration in the axial direction, the gaps h ₁ and h ₂ and the exhaust hole 18 are required to obtain the conductance C ₀ satisfying Δx <x ₀ . And generally, the gap h _1, h ₂ of the voice coil motor C yoke member 10a and the magnet 11 and the sleeve 17, because it is to some extent limited by thrust like, to obtain a conductance C ₀ required, the exhaust hole 18 It is necessary to determine the diameter d according to design conditions. When there is one or a plurality (n) of the exhaust holes 18 having the same shape, the diameter d of the exhaust holes 18 is expressed by Expression 2.

[0019]

(Equation 2) Here, eta is the viscosity coefficient of the gas, l the length (≒ the thickness of the coil head 16) of the exhaust hole 18, p _m is the average pressure and external pressure of the inner coil assembly B, n is an exhaust hole 18 (N = 1, 2, 3,...). That is, depending on ΔP
The axial displacement [Delta] x, the relationship between the allowable value x _0, delta
x <conductance of the exhaust hole 18 such that _{x 0 C 2}
(= C ₀ −C ₁ ) and the diameter of the exhaust hole 18 is determined,
Axial vibration can be suppressed, positioning
Accuracy and positioning time can be improved.

In general, increasing the control system gain of the servo control system in the positioning device is important for improving the servo performance in the positioning accuracy, the positioning speed, the stability of the control system against disturbance, and the like. , in the conventional design method, the natural frequency f of the mechanical system is set to more than 3 times the control frequency f _0. However, depending on the frequency characteristics (attenuation characteristics) of the mechanical system, control is possible even at about twice. Therefore, also in the linear drive device of the present invention, the mechanical system is required to have a frequency characteristic such that the natural frequency has a value equal to or more than two to three times the control frequency. When providing the exhaust hole 18 in the closed space V surrounded by the coil assembly B (VCM coil), the coil assembly B, the bearing housing 1, and the porous bearing members 2a, 2b
Natural frequency (feed system rigidity) in a system composed of a linear motion bearing composed of a shaft and the shaft 5 supported thereby.
Is expressed by a function f (m, c, k) of the mass m, the damping coefficient c, and the rigidity k of the moving body. Therefore, when the control frequency is f ₀ , f (m, c, k) ≧ 2f ₀ Shape within the range,
The dimensions and number must be determined. This m, c, k
Varies depending on the shape, size, and number of the exhaust holes 18. In other words, the characteristic frequency f (m, c, k) is considered to be a function of the shape, size, and number of the exhaust holes 18.
The upper limit value of the shape, the size, and the number of the exhaust holes 18 is limited by the above value.

The voice coil motor is originally an optimal motor for directly driving the driven body, and is designed so as to be arranged in accordance with the position of the center of gravity of the driven body. The coil of the voice coil motor is attached to the driven body and becomes a part of the driven body. Therefore, if the imbalance in the weight of the coil is large, the position of the center of gravity of the driven body as a whole is shifted toward the thrust acting on the coil. For this reason, when the position of the exhaust hole 18 is provided in the coil head 16, for example, as shown in FIGS. 5A and 5B, it is desirable that the position be balanced. In the case of a load, as shown in FIG.
It is desirable to arrange so that the lower side is heavier than the drive axis.

According to the present embodiment, 1) Since the shaft and the gas bearing are disposed inside the voice coil motor C, there is no overhang on the bearing of the drive system and the moment load is minimized, so that high accuracy is achieved. Feeding can be performed, and the size of the apparatus can be reduced.

2) Since the linear encoder D is arranged close to the mounting surface 19a on which the measuring instrument or the like is mounted, the linear encoder D is less susceptible to deformation of the shaft due to a temperature change, and high-precision feeding is possible.

3) Since the non-rotating unit is arranged outside the bearing housing 1 and is composed of a flat hydrostatic gas bearing and a flat guide, the manufacturing and assembling adjustment work is easy, and the feed accuracy of the shaft is improved. It is possible to restrict the degree of freedom of rotation without deteriorating the posture accuracy.

4) By providing the lock mechanism by the air cylinder 30, even if the supply of the pressurized gas is stopped due to a malfunction of the apparatus or a human error and the shaft and the bearing come into contact, the shaft can be fixed. Damage to the bearing surface and the shaft surface can be prevented.

5) Since the shaft and the bearing have circular cross-sections, the number of parts is small, and the gap can be managed by the precision of the parts.

6) By providing the exhaust hole 18, the exhaust efficiency is improved in the closed space V surrounded by the coil.
The displacement in the axial direction of the coil and the shaft due to the pressure change due to the volume change of the closed space V during the positioning drive is reduced, so that the axial vibration can be suppressed to be small, and the positioning accuracy and the positioning time can be improved. Become.

7) When the exhaust hole 18 is provided, the natural frequency f of the mechanical system becomes f ≧ 2f with respect to the control frequency f ₀ .
_Since the shape, size, and number of the exhaust holes 18 are determined so as to be _zero , the mechanical system can sufficiently follow the control command without reducing the feed rigidity of the mechanical system. Accurate and high-speed positioning is possible .

FIG . 6 shows another embodiment. Same members as in FIG.
The description of is omitted. Reference numeral 35 denotes a bearing housing made of a magnetic material, which also serves as the inner yoke 10b in FIG. 1 of the magnetic circuit assembly C of the voice coil motor. According to the above configuration, the bearing housing forms a part of the magnetic circuit assembly, so that the size can be further reduced. In the above description, the gas bearing is a porous bearing member 2a, 2b, 2
Although the porous restrictors 6a and 26b are used, other restricting forms such as self-contained restrictor, surface restrictor, and orifice restrictor may be used. Further, the lock mechanism is not limited to a system using an air cylinder, and may be another system.

[0030]

[0031]

[0032]

[0033] Incidentally, the shape of the exhaust hole 18 was rounded in the above description, as long afford the desired conductance C _2, may be of any shape. In addition, the cross-sectional shape of the shaft is round in the above-described embodiment in order to realize a small size and low cost, but in order to obtain the effect of the present invention by providing the exhaust hole, the cross-sectional shape of the shaft is required. The shape may be polygonal. The applicable linear drive device is not limited to one axis, and may be a two-axis configuration .

[0034]

[0035]

As described above , the static pressure gas bearing as the main mechanism and the shaft having a circular cross section supported by the static pressure gas bearing are arranged inside the magnetic circuit assembly of the voice coil motor . By arranging a mechanism other than the main mechanism outside the shaft and the bearing, 1 ) an inexpensive and high-precision linear drive device can be realized by means of a rotational degree-of-freedom restraining means that facilitates production and assembly adjustment work. Furthermore, it is necessary to make the mechanisms other than the main mechanism compact.
Means to restrict the degree of freedom of rotation of the shaft (around
Stop mechanism), the configuration is the same as a flat hydrostatic gas bearing.
By adopting a simple shape using a plate-like guide, 2) the entire apparatus can be reduced in size.

A linear drive having the above-mentioned main mechanism
Respect, by providing the mechanism for locking the movable body (shaft), in addition to the above effects, 3) due to malfunction of the device and human error and the like, to stop the supply of pressurized gas, the shaft and the bearing is closer In such a state, even if an external force or the like acts on the device, the shaft does not move in the contact state, and there is an effect that damage to the shaft and the bearing can be prevented.

Further, since an exhaust hole is provided to communicate with the outside from the closed space surrounded by the coil of the voice coil motor, or the exhaust hole has a predetermined conductance, the efficiency of exhaust from the closed space is improved. In addition, the axial displacement of the coil and the shaft due to the pressure change due to the volume change of the closed space at the time of the positioning drive is reduced, the axial vibration is suppressed, and the positioning accuracy and the positioning time are improved. Further, the feed rigidity of the mechanical system is reduced by determining the upper limit of the shape, size, and number of the exhaust holes so that the natural frequency f of the mechanical system becomes f ≧ 2f ₀ with respect to the control frequency f ₀ . In addition, there is an effect of improving positioning accuracy and positioning time.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional configuration diagram of a linear drive device according to an embodiment of the present invention.

FIG. 2 is a view in the direction of arrow X in FIG. 1;

FIG. 3 is a cross-sectional view of a detent unit according to the embodiment of the present invention.

FIG. 4 is a view as seen in the direction of the arrow Y in FIG. 2;

FIG. 5 is an explanatory view of an arrangement of exhaust holes of the apparatus of FIG. 1;

FIG. 6 is a partial sectional configuration diagram of a linear drive device according to another embodiment of the present invention.

FIG. 7 is an explanatory diagram of a conventional technique.

DESCRIPTION OF SYMBOLS 1; bearing housing, 2a, 2b; porous bearing member, 5; shaft, 18; exhaust hole, 24; guide plate, 26a, 26b; porous bearing member, 27; holding member, 30; Cylinder, 32; clamp head, 3
3; clamp base, 34; leaf spring, C: voice coil motor, D: linear encoder, E: non-rotating unit, h
Between the gap; _{1, h 2.}

Continuation of the front page (56) References JP-A-2-202348 (JP, A) JP-A-2-22082 (JP, U) JP-A-3-3175 (JP, U) (58) Fields surveyed (Int) .Cl. ⁶ , DB name) H02K 33/18

Claims (10)

(57) [Claims] 1. A linear drive device for positioning a shaft in a predetermined direction by a static pressure gas bearing and a voice coil motor, wherein the static pressure gas bearing and a shaft supported by the static pressure gas bearing are connected to each other by a voice coil motor. A linear drive device disposed inside a magnetic circuit assembly, wherein a lock mechanism for restricting a degree of freedom in a moving direction of a shaft is provided. 2. The linear drive device according to claim 1, wherein said lock mechanism is constituted by an air cylinder. 3. The air cylinder is fixed to a bearing housing side and clamps a member fixed to the shaft side when supply of pressurized gas to the hydrostatic gas bearing is stopped. The linear drive according to claim 2. 4. The linear drive device according to claim 1, wherein the bearing housing of the hydrostatic gas bearing also serves as a yoke of a magnetic circuit assembly of the voice coil motor. 5. The linear drive according to claim 1, characterized in that a vent hole leading to the outside from the closed space surrounded by the voice coil motor coil. 6. The linear drive device according to claim 5, wherein a part of the gas ejected from the hydrostatic gas bearing is discharged into the closed space. 7. A shape and a size of the exhaust hole include a flow rate Q corresponding to a volume change per unit time of the closed space at the time of positioning driving, and a flow rate Q corresponding to a conductance C _2.
And the amount Δx by which the coil and the shaft are moved in the axial direction by a force generated by the pressure change ΔP inside the closed space to be discharged from the exhaust hole.
If, linear drive according to claim 5, characterized in that it is determined from the allowable value x ₀ Metropolitan design of axial oscillations in the linear drive. 8. between each parameter, the atmospheric pressure P _a
If Q = C ₂ · ΔP / P _a , and if the length of the closed space in the axial direction is L, Δx = ΔP · L / P _a
The relationship holds is, [Delta] x <linear drive according to claim 7, wherein the conductance C ₂ of the x ₀ is the shape and size of the exhaust hole as obtained. 9. The shape, size and number of the exhaust holes are determined by a natural frequency f of a system composed of a coil of a voice coil motor, a hydrostatic gas bearing, and a shaft supported by the same, and a control frequency f. ₀ and linear drive according to claim 5, wherein the f ≧ 2f ₀ the relationship is within the range established during. 10. A linear drive according to claim 5, wherein the bearing housing of the externally pressurized gas bearing also serves as a magnetic circuit assembly of the yoke of the voice coil motor.