JP5454289B2 - Hydraulic levitation trapezoidal screw - Google Patents

Description

  This is a trapezoidal screw structure that efficiently converts the rotational motion of a motor into straight motion and its control method, and can be used as a drive unit for a die casting machine, an injection molding machine, or a machine tool.

  An electric motor has been used for a long time as a drive source for industrial machines and the like. A screw mechanism is adopted as a mechanism for converting the rotary motion of the electric motor into a straight motion, and the speed control and the pressure (propulsion force) control of the linear motion portion are performed by controlling the rotation speed and torque of the electric motor. In particular, trapezoidal screws are often used for the screw mechanism. Trapezoidal screws have the advantage that they are easy to process and can be manufactured at low cost. However, because the sliding frictional resistance due to metal contact between the thread surfaces (flank surfaces) is large, the ratio of the linear energy output to the input rotational energy is high. There was a problem that the conversion efficiency was very poor, around 30%.

In order to solve such a problem, a ball screw of a type in which a steel ball is fitted between a screw shaft and a screw thread of a nut and the ball is circulated by a return tube has been developed and widely used. In the ball screw, since the rolling of the ball is interposed between the screw shaft and the nut, the frictional resistance is very small, and a conversion efficiency exceeding 90% is achieved. Therefore, for example, it is generally used for a feed mechanism of a machine tool or a drive mechanism of an electric injection molding machine.
However, in the case of a ball screw, there is a problem in that if the ball screw operates at a high speed, the ball itself is damaged due to an impact caused by the collision between the balls, causing a failure of the ball screw and the machine. Therefore, there is a limit value in the peripheral speed, which is a numerical value (D × N) obtained by multiplying the outer diameter (Dmm) of the ball screw shaft and the rotational speed (N rpm), and the thickness and rotational speed of the ball screw shaft are limited. . Therefore, it is not suitable for a high-speed and heavy load (screw shaft has a large diameter) device, and there is a drawback that a ball screw cannot be used for a large machine. In addition, even when a plurality of ball screws are used and the load per one is lowered, the mechanism or control of the shafts becomes complicated, and it is difficult to adopt it due to an increase in cost.

In addition, drill holes for supplying fluid between the flank surfaces from the inside of the trapezoidal screw nut are provided, and fluid pressure such as air and hydraulic oil is supplied appropriately to reduce the metal contact force on the flank surface. Static pressure screws are used.
For example, in Patent Document 1, hydraulic pressure is applied to both flank surfaces via a peripheral step (throttle clearance) provided between the inner periphery of the outer cylinder and the outer periphery of the nut and a small hole provided in the nut. There has been disclosed a static pressure screw capable of generating a fluid film having a certain thickness on the flank surface by supplying and generating a hydraulic pressure corresponding to fluctuations in the axial load in a balanced manner.
Next, in Patent Document 2, the pressure air supplied from the nut side to the flank surface is discharged from a longitudinal exhaust hole provided on the axis of the screw shaft, and the necessary air is ensured by sufficiently securing the discharge amount. A hydrostatic air screw that can form a membrane is disclosed.
Furthermore, in Patent Document 3, the axial load is detected by two pressure detectors provided in the bearing portion, and after the detection signal is amplified by a differential amplifier, a signal is directly input to the servo valve to obtain the axial load. A hydrostatic screw device technology for supplying corresponding hydraulic pressure to each flank surface of a nut is disclosed.

JP 57-15144 A JP 58-166161 A JP 59-190561 A

However, in the screw described in Patent Document 1, since the pressure on the flank surface is adjusted by the squeezing clearance, the generated pressure varies due to the manufacturing error of the height of the squeezing clearance and the fluctuation of the hydraulic oil temperature. This pressure could not be generated.
In addition, the screw described in Patent Document 2 is not suitable for a high-load screw device that requires a high pressure because the pressure is released from the exhaust hole.
Furthermore, in the screw described in Patent Document 3, the servo valve is directly operated by an electric signal output from the pressure detector, so that the pressure on the flank surface is appropriately controlled with respect to loads ranging from low loads to high loads. It was difficult.
Therefore, the invention of the present application supplies the hydraulic pressure corresponding to the axial load to the flank surface of the trapezoidal screw and floats it, thereby ensuring that the flank surfaces are not in contact with each other. The present invention also provides a hydraulically levitated trapezoidal screw and a control method thereof.

In the first invention of the present application, a trapezoidal screw composed of a screw shaft and a nut, an outer diameter sealing material that seals between an outer diameter portion of the screw shaft and a screw bottom portion of the nut, a root diameter portion of the screw shaft, Sealed by an inner diameter sealing material that seals the inner diameter portion of the nut, and a flank surface sealing material that seals between the flank surface of the screw shaft and the flank surface of the nut at both ends of the nut. Hydraulic control device for supplying hydraulic oil individually controlled in pressure to spiral a group oil chamber and b group oil chamber, a group oil chamber and b group oil chamber formed between the flank surfaces A passage hole provided in the nut for communicating with the a-group oil chamber and the b-group oil chamber and supplying hydraulic pressure from the hydraulic control device, and a screw for measuring the axial position of the screw shaft and the nut. position It is composed of a Nsa, and feeding back the measured values of the screw position sensor during operation of the trapezoidal thread, is formed on both sides of the threads of the screw shaft, so that the spacing between the flanks is substantially the same, the hydraulic control and trapezoidal screw that controls individually the pressure of the hydraulic fluid supplied to a group oil chamber and b group oil chamber by the device.
In the second invention, the hydraulic control device has two independent hydraulic oil discharge lines, and each hydraulic oil discharge line is a trapezoidal screw provided with hydraulic oil discharge means and pressure control means.
Furthermore , in the third invention, the screw shaft is connected to the rotating shaft of the electric motor, and the nut is slidable in a state where the rotation is restricted.
And in 4th invention, it uses for the die-casting machine or injection molding machine which converts the rotational motion of a motor into a rectilinear motion, and drives.

(1) Since there is no restriction on the peripheral speed or the like, it is possible to realize a screw feed mechanism that can move at high speed and can exert a large propulsive force.
(2) Since the frictional resistance due to metal sliding on the flank surface of the screw is eliminated, the rotational torque of the motor can be efficiently converted into a linear motion force (propulsion force).

It is an Example of this invention, and is a figure which shows a trapezoid screw and its peripheral components. It is a figure which shows the detail of the cross section of a screw shaft and a nut, and a hydraulic circuit. It is a figure which shows the detail of the part which seals between flank surfaces. In FIG. 3, it is the figure seen from the arrow P.

  Embodiments relating to a hydraulically levitated trapezoidal screw according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an embodiment of a structure when a trapezoidal screw according to the present invention is incorporated in a mechanical device.
A bearing fixing member 23 is fixed on the frame 18 of the mechanical device. An electric motor 20 is fixed to the bearing fixing member 23 via a motor mounting bracket 22, and the rotating shaft of the electric motor 20 is connected to the screw shaft 10 by a coupling 21. A thrust bearing 24, an angular bearing 25, a spacer therebetween, and a bearing nut 26 are assembled to the left end of the screw shaft 10 in FIG. 1, and the screw shaft 10 is attached to the bearing fixing member 23 in a state of being freely rotatable and restrained in the axial direction. It is supported. When a leftward thrust load is applied to the screw shaft 10, the load is received by the thrust bearing 24, and when a rightward force is applied, the load is received by the angular bearing 25. The angular bearing 25 is pressed against the bearing fixing member 23 by a bearing press 27.
On the other hand, a bearing 31 is attached to the right end portion of the screw shaft 10 by a presser nut 32 and is rotatably supported by a bearing support member 30 fixed on the frame 18.

  A moving member 13 of the mechanical device is attached to the nut 11 that is screwed with the screw shaft 10, and the rotational drive of the electric motor 20 is transmitted as a linear motion of the mechanical device. Since the slide block 34 is attached to the moving member 13 and becomes slidable in combination with the slide rail 33 attached to the frame 18, the nut 11 and the moving member 13 are in a state in which the rotation is restricted. And it is possible to go straight ahead.

FIG. 2 is a cross-sectional view of the threaded portion of the screw shaft 10 and the nut 11 and a hydraulic circuit that supplies hydraulic pressure between the flank surfaces of the screw.
A trapezoidal screw that is screwed together is formed on the outer periphery of the screw shaft 10 and the inner periphery of the nut 11. The trapezoidal screw is an open screw with a gap between the flank surfaces, and can guide the hydraulic oil to a space of δ mm in the axial direction. The gap is preferably about 2 mm with 2δ on both sides. The inner diameter portion 11 b of the nut 11 is processed with a groove for accommodating the inner diameter sealing material 51, so that the gap between the inner diameter portion 11 b of the nut 11 and the valley diameter portion 10 b of the screw shaft 10 can be sealed. Further, a groove for accommodating the outer diameter sealing material 52 is processed in the screw bottom portion 11a of the nut 11, so that the space between the screw bottom portion 11a of the nut 11 and the outer diameter portion 10a of the screw shaft 10 can be sealed. Yes. Further, two sets of flank surface sealing materials 70 for sealing between the flank surfaces are mounted at both ends of the nut 11. Therefore, from the a1 group oil chambers which are gaps between the flank surfaces a1, a2, a3, a4, a5 and whose periphery is sealed (sealed), and similarly from b1, b2, b3, b4, b5 The b group oil chamber is formed. In the a group oil chamber, the oil chamber becomes small when the nut 11 receives a load from the arrow A direction in the figure, and in the b group oil chamber, the oil chamber becomes small when the load from the arrow B direction in the figure receives. The inner diameter sealing material 51 and the outer diameter sealing material 52 are spiral. The a group oil chamber and the b group oil chamber are formed on both sides of one screw thread.

The a-group oil chamber is connected to the hydraulic device via the a-line which is an external pipe through the a-line passage hole 47 provided in the nut 11. The b group oil chamber is also connected to the hydraulic device via the b line passage hole 48. The a line is connected to the a line pump 43 that is rotationally driven by the pump motor 45, and is branched in the middle to be connected to the a line electromagnetic pressure control valve 41 and the tank 46. Therefore, the hydraulic oil discharged from the a-line pump 43 is pressure-controlled by the a-line electromagnetic pressure control valve 41, and the hydraulic oil having a desired pressure can be supplied to the a-group oil chamber. The a-line electromagnetic pressure control valve 41 is electrically connected to a control device (not shown), and the set pressure can be freely changed by a command from the control device.
Similarly, the b group oil chamber is also connected to the b line pump 44, the b line electromagnetic pressure control valve 42, and the tank 46 through the b line passage hole 48 and the b line, so that the hydraulic pressure can be controlled. .

  The a-line pump 43 and the b-line pump 44 are rotated by a pump motor 45 to suck up hydraulic oil from the tank 46 and discharge it to the a-line and b-line. The a group oil chamber and the b group oil chamber are sealed (sealed and sealed) by the respective sealing materials, so that the pressure is reliably increased, and there is almost no leakage of high pressure oil. And the capacity | capacitance of the motor 45 for pumps can be made small. Accordingly, the power consumption of the pump motor 45 is reduced.

  A screw position sensor 60 is attached to the end surface of the nut 11, and a distance between the screw shaft 10 and the screw thread can be measured. Thereby, the relative position of the screw shaft 10 and the nut 11 in the axial direction can be measured, and each gap between the a group oil chamber and the b group oil chamber can be detected. The screw position sensor 60 is also electrically connected to the control device so that the measured value can be transmitted instantaneously and continuously.

  FIG. 3 shows details of the flank face seal portion. A substantially cylindrical seal adapter 71 having a slit groove 73 is embedded and fixed in the nut 11. A plate-like flank sealing material 70 is fitted in the slit groove 73 of the seal adapter 71 so as to be slidable and almost free of gaps, and is pressed against the flank surface of the screw shaft 10 by a spring 72. Since steel is suitable for the material of the screw shaft 10, the flank face seal 70 is preferably made of copper. Since copper is slightly softer than steel, when the screw shaft 10 rotates, the flank surface seal 70 material and the flank surface of the screw shaft 10 rub against each other, but can be effectively sealed without causing damage to the flank surface. it can.

  FIG. 4 shows a cross section of the center line of the seal adapter 71 in FIG. A slit groove 73 is machined in the lower part of the seal adapter 71, and a flank surface sealing material 70 is inserted and supported therein, and is pressed downward by a spring 72 from above. The seal adapter 71 can form a trapezoidal screw continuous with the nut 11 by subjecting the inner diameter portion to threading in a state of being incorporated in the nut 11. Thereafter, the seal adapter 71 is taken out and the slit groove 73 is preferably processed. Here, the spring 72 is used to press the flank surface sealing material 70 against the flank surface of the screw shaft 10. For example, hydraulic oil supplied to the flank surface oil chamber is guided to the upper side of the flank surface seal 70 to It is also possible to make a structure that presses against the flank surface by force.

Next, the operation control method of the hydraulic levitation trapezoidal screw described above will be described.
When the operation start signal is input to the control device, the pump motor 45 is first driven to rotate, and hydraulic oil is discharged from the a-line pump 43 and the b-line pump 44. At this time, the a-line electromagnetic pressure control valve 41 and the b-line electromagnetic pressure control valve 42 are set to low pressures. As a result, a low pressure is supplied to the a group oil chamber and the b group oil chamber. In this state, the screw position sensor 60 measures the gap between the flank surfaces. Then, the pressure of the line with the smaller gap is adjusted slightly higher so that each gap has an intermediate value of δ mm. Then, the electric motor 20 is rotated to move the nut 11 and the moving member 13 straightly. At this time, since the gap changes due to fluctuation of the force acting on the moving member 13, the relative position is constantly monitored by the screw position sensor 60, and the command values of the a-line electromagnetic pressure control valve 41 and the b-line electromagnetic pressure control valve 42 are appropriately set. Change and increase or decrease the pressure in each line. For example, when the measured value of the screw position sensor 60 becomes small, the gap in the a group oil chamber is reduced due to the load in the direction of arrow A, and the hydraulic oil falls into the tank 46 via the a line electromagnetic pressure control valve 41. Therefore, the set pressure of the a-line electromagnetic pressure control valve 41 is increased.
Such a process is repeated at a short sampling interval, and control is performed so that the gap on both sides can always be maintained around δ mm.

Here, the relationship between the propulsive force (load) of the mechanical device and the pressure of the oil chamber will be described.
If the axial thrust is Q, the outer diameter of the screw shaft is d, the height of the engaged threads is h, and the number of threads that supply pressure to the flank is Z, the flank (oil chamber) The pressure q of the hydraulic oil to be supplied is as follows.
q = Q ÷ {π · Z · h · (d−h)}
From the above formula, the maximum pressure is calculated from the specification value of the maximum propulsive force of the mechanical device, and a hydraulic circuit that can supply the maximum pressure is designed.

By creating and controlling the trapezoidal screw having the above-described configuration, the hydraulic oil is always interposed between the flank surfaces, and the metal contact between the flank surfaces is eliminated, so that the screw device rotates smoothly. Further, there is no peripheral speed limitation for reducing the collision between balls such as a ball screw, and it becomes possible to drive a large apparatus that operates at high speed and with a high load. Furthermore, since the oil chamber of the screw portion is sealed with the sealing material, there is little leakage of the high-pressure hydraulic oil, and the power consumption of the pump motor can be reduced.
For this reason, it can be used as a driving device for a large-sized machine such as a die casting machine or an injection molding machine (for example, a clamping force of 500 tons or more), and the clamping apparatus and the injection apparatus can be moved.

  The above-described embodiment is an example of the present invention, and the present invention is not limited by the embodiment, but is defined only by matters described in the claims, and other embodiments than the above are also possible. It can be implemented.

  It can be used in die casting machines and injection molding machines that are driven by a combination of servo motors and screws.

DESCRIPTION OF SYMBOLS 10 Screw shaft 10a Outer diameter part 10b Valley diameter part 11 Nut 11a Screw bottom part 11b Inner diameter part 13 Moving member 18 Frame 20 Electric motor 21 Coupling 22 Motor mounting bracket 23 Bearing fixing member 24 Thrust bearing 25 Angular bearing 26 Bearing nut 27 Bearing presser 30 bearing support member 31 bearing 32 retaining nut 33 slide rail 34 slide block 41 a line electromagnetic pressure control valve 42 b line electromagnetic pressure control valve 43 a line pump 44 b line pump 45 pump motor 46 tank 47 a line passage hole 48 b line channel hole 51 outer diameter sealing material 52 inner diameter sealing material 60 screw position sensor 70 flank surface sealing material 71 seal adapter 72 spring 73 slit groove

Claims (4)

A trapezoidal screw consisting of a screw shaft and a nut,
An outer diameter sealing material that seals between an outer diameter portion of the screw shaft and a screw bottom portion of the nut, an inner diameter sealing material that seals a valley diameter portion of the screw shaft and an inner diameter portion of the nut, and both end portions of the nut And a flank sealing material that seals between the flank surface of the screw shaft and the flank surface of the nut, and is formed between the flank surface of the screw shaft and the flank surface of the nut. A group oil chamber and b group oil chamber,
A hydraulic control device for supplying hydraulic oil individually pressure-controlled to the a group oil chamber and the b group oil chamber;
A flow path hole provided in the nut for communicating with the a group oil chamber and the b group oil chamber, and supplying hydraulic pressure from the hydraulic control device;
A screw position sensor for measuring the relative position of the screw shaft and the nut in the axial direction;
Consisting of
The hydraulic control device feeds back the measured value of the screw position sensor during the operation of the trapezoidal screw so that the distance between the flank surfaces formed on both sides of the thread of the screw shaft is substantially the same. wherein a group oil chamber and trapezoidal screw which is characterized that you individually control the pressure of hydraulic fluid supplied to the b group oil chamber. The trapezoidal screw according to claim 1, wherein the hydraulic control device has two independent hydraulic oil discharge lines, and each hydraulic oil discharge line includes hydraulic oil discharge means and pressure control means. . The trapezoid according to any one of claims 1 and 2, wherein the screw shaft is connected to a rotating shaft of an electric motor, and the nut is capable of sliding movement in a state in which rotation is constrained. screw. The trapezoidal screw according to any one of claims 1 to 3, wherein the trapezoidal screw is used in a die casting machine or an injection molding machine that is driven by converting a rotational movement of a motor into a linear movement.

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