JPS63200904A - Spindle head balancing device - Google Patents

Abstract

PURPOSE:To position an acting point at a neutral point constantly so as to prevent reduction of a resonance number by adjusting balance force relative to change of weight of a spindle head corresponding to the output of an error counter by means of a switching element which is energized only when the head is stopped. CONSTITUTION:If a position command value is zero when a spindle head 1 is stopped, a reversing torque acts on a ball spring 7 because of suspension by a load W, and the spindle head 1 descends until it balances with the output torque of a drive motor 8, where a position deflection quantity DELTAZ is produced, detected by a linear scale 25, and fed back to an error counter 26, so an error output signal is amplified to act on the drive motor 8 as a voltage. The deflection quantity DELTAZ is transmitted to a hold circuit 30 to be an input control voltage to an electropneumatic pressure converter 31, and an air pressure in proportion to the input acts on a diaphragm 24a to adjust pressure from a compressor 22 and act on a piston 18 to produce a balance force F. Therefore the spindle head 1 moves upward, and the deflection quantity DELTAZ is reduced, and when it becomes zero, a switching element 28 gets off.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for controlling the weight balance of a spindle head in a machine tool, electrical discharge machining device, or other similar processing machine.

[Prior Art] Conventionally, in the case of a machine tool having a vertical head for mold making, for example, in order to reduce the load current of its drive unit, for example, a DC motor unit, a machine tool as shown in FIG. 4 is generally used. A balance weight method is used. The balance weight system has two main effects: one is that it can reduce the load current of the drive motor, which suppresses thermal expansion of the ball screw, etc. due to heat generated by the motor, and the other is that it reduces the neutral point of the control range of the drive amplifier. This is an improvement effect on the drive unit side, such as the ability to set the operating point under load nearby and improve the controllability of the spindle head. The other one is that the load on the ball screw and its bearings can be reduced, which can improve the lifespan, and the mechanical design (shape, size, etc.)
This has design advantages such as ease of use.

Next, these points will be explained.

In Fig. 4, 1 is the spindle head, 2 is the spindle, 3a is the processing tool attached to the lower end of the spindle 2, which is the most frequently used average tool, and 3b is the tool with the maximum usable weight. The case is shown below. This spindle head 1 is mounted on the side surface of a column 4 via a slide bearing 5 so as to be able to slide up and down, and is attached to a nut member 6 protruding from the side surface of the spindle head 1.
A ball screw 7 is screwed into the shaft, and the ball screw 7 is rotated by a drive motor 8 such as a DC motor to move the spindle head 1 up and down. In this case, in order to balance the weight of the spindle head 1, a balance weight 9 is attached to the spindle head 1 via a wire rope or chain 10 and a plurality of pulleys 11 on the opposite side of the ball screw 7.
is connected to. The weight of balance weight 9 is usually
It is set to a value that is the sum of the loads of the spindle head 1 and the most frequently used average tool 3a.

Therefore, the position control of the spindle head 1 is achieved by connecting the rotary encoder 12 to the ball screw 7, inputting the rotation angle number of the ball screw 7 detected by the rotary encoder 12 to the preamplifier 13, and calculating the deviation from the command value. This is done by amplifying the amount by the drive amplifying section 14 and applying the output to the drive motor 8 as a control voltage.

By the way, if the load on the tool 3a changes more than the initially set load, for example, since non-rotating machining is generally performed on electrodes of electrical discharge machining equipment, the load may change from several hundred gf to several hundred kgf per electrode. In such cases, even if the position command value is zero, the drive motor 8
The suspended load was initially V (kgf) but became W'
(kgf), the position deviation is detected by the rotary encoder 12 and fed back and amplified, so the operating point of the drive amplifier 14 is set to the load current I
It will move to and stop. This can be expressed by the following equation.

VoK φ K ・ΔZ A D/A However, W': Actual load (suspended load) T: Drive motor output torque P: Ball screw lead O: Drive motor applied voltage R: Armature resistance KT: Torque constant KA: AMP amplification coefficient K: Digital/analog conversion rate D/A ΔZ: Position deviation amount This position deviation amount ΔZ is proportional to the suspended load W' from the above equation, so the load operating point of the drive amplifier 14 is lower than the neutral point. This results in a large deviation and bias in the control range. This results in the disadvantage that stable control cannot be obtained. As a countermeasure against this, a bias current adjustment section 13a is provided in the preamplification section 13.
A bias current is applied to the drive motor 8 so that when the spindle head 1 is stopped, the feedback signal from the rotary encoder 12 becomes zero and the operating force appears to be at a neutral point. However, even in this case, current will always flow through the drive motor 8. For example, if the load current is close to the motor's rated value, an overload will occur during machining, causing problems such as burnout of the motor coil and abnormal heat generation. This will induce

When the tool weight changes greatly in this way, the bias current is set by assuming the midpoint between the minimum tool load and the maximum tool load in the design, so during actual use the operating point moves to + or Ichijo. As described above, a point away from the neutral point of the control range of the drive amplifying section becomes the operating neutral point under load.

Next, if a balance weight 9 equivalent to a suspended load W' which is sent up and down by a drive motor 8 is connected to the spindle head 1 with a wire rope 10 and suspended, a ball screw 7 and a bearing part (see Fig. (not shown) is extremely light, and the only resistance that acts during vertical movement is the sliding resistance of the bearing section and the slide bearing 5. Therefore, the size of the ball screw 7 and the load capacity of the bearings can be reduced, or the lifespan can be extended. However, in this case as well, a relative load difference occurs between the spindle head 1 and the balance weight 9 between the minimum tool load and the maximum tool load, and the ball screw 7
A downward or upward thrust load will act on this, and therefore, the maximum unbalanced load will be the design reference value.

By the way, in the main spindle head of a general machine tool, constant feed is the main operating mode during machining, and even in setup work such as positioning, constant speed feed is basic, although there are high and low speeds. However, in addition to constant-speed feed during positioning and setup work, the spindle head of electrical discharge machining equipment has a function called a "pole gap servo" that maintains a constant discharge gap between the workpiece and the tool during machining. The response of the inter-servo servo greatly affects machining performance. This means that when the tool and workpiece are short-circuited, they must be quickly separated to return to a normal gap, and when the gap is in the so-called open state, it is necessary to rapidly approach them. The machining performance (speed) can be improved by improving the responsiveness of the drive system of the spindle head and increasing the machining efficiency in response to these ever-changing changes in the gap. When the spindle head repeatedly moves up and down due to relative approach and separation within a very short gap like this, it is affected by the mechanical resonance of the first mode set by the wire rope 10 and the balance weight 9, and the response is improvement will be limited. As a practical matter, this response needs to be in the range of several Hz to several tens of Hz in the case of electric discharge machining, but the primary resonance frequency of the run weight also often falls within this range. In many cases, it is difficult to increase the size of the pulley 11 and increase the primary resonance frequency due to the size of the pulley 11, the radius of curvature, etc. This is because although the load is close to zero, in the vibration system, the mechanical resonance frequency decreases to about 1/, /=7 due to the increase in mass, as shown in the following equation.

However, K: mechanical rigidity g: gravitational acceleration W': suspension load WB: weight of balance weight [Problem to be solved by the invention 1 As described above, the conventional balance weight system for spindle heads has the following problems. There will be problems.

■ If the weight of the tool or electrode changes, the control neutral point of the drive amplification section will fluctuate significantly, making it impossible to obtain stable control characteristics.

■ When viewed as a drive system, the mass increases by the mass of the balance weight, which affects the mechanical resonance frequency, and there is a limit to the improvement of response.

The present invention was made to solve these conventional problems, and uses a balance method using mechanical force instead of the conventional balance method using weights, and the weight of the machining tool (including electrodes; the same applies hereinafter). It is an object of the present invention to provide a balance device for a spindle head that can automatically adjust balance force according to changes.

[Means for Solving the Problems] The spindle head balance device according to the present invention uses a fluid pressure cylinder device instead of a conventional balance weight, and a wire rope that connects the piston of the cylinder device and the spindle head to form a closed loop. The cylinder device is equipped with a control valve that controls the supply pressure, and the position of the spindle head is determined based on the output of an error counter that subtracts the detected value from the position detector and the command value. A switching element is configured to control the motor and is conductive only when the spindle head is stopped, and the pressure is controlled to the control valve via the switching element in accordance with the output of the error counter. It is equipped with a hold circuit that operates as follows.

[Function] In the spindle head balance device according to the present invention, the hold circuit is configured to control the pressure of the cylinder device according to the output of the error counter using a switching element that becomes conductive only when the spindle head is stopped. Since the supply pressure of the cylinder device is adjusted through the control valve in response to changes in the weight of the spindle head, the operating point of the spindle head is always the neutral point of the drive control section.

[Example] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram of an embodiment of the present invention.

In the figures, the same reference numerals as in FIG. 4 indicate the same or corresponding parts.

This embodiment shows an example in which an air cylinder device 16 is used in place of the balance weight described above. The cylinder 17 of this air cylinder device 16 has one end open to the atmosphere and is firmly fixed to the column 4. Rods 19 and 20 are connected to the piston 18 which is slidably fitted into the cylinder 17.
Each end of the wire rope 10 is connected to each end of the wire rope 10, and the other end of the wire rope 10 is connected to the nut member 6 of the spindle head 1 via a plurality of pulleys 11 to form a closed loop.

A diaphragm control valve 24 for controlling the pressure P (MPa) in the cylinder 17 is connected to a pneumatic system whose supply source is the compressor 22 of the cylinder device 16 .

In other words, the pressure P in the cylinder 17 is controlled as the output pressure of the diaphragm control valve 24, and the output is F-P ratio A. However, F: balance force A: pressure receiving area of the piston, and in design, this balance force F is The total load W of the spindle head 1 and the processing tool 3a is made to match. Therefore, the drive motor 8 of the spindle head 1 is only required to have the total torque of the torque that generates the acceleration necessary for the vertical movement of the spindle head 1, and the torque that overcomes the sliding resistance of the slide bearing 5, pulley 11, etc. becomes.

The movement of the spindle head 1 is controlled by the drive motor 8 by a control circuit mainly composed of a preamplifier 13 and a drive amplifier 14. During this control, the position of the spindle head 1 is measured using a linear scale using a linear position detector 25. The detected position signal is fed back to the error counter 26.

The error counter 26 subtracts the feedback position signal from the initially set command value. error counter 2
6, that is, the droop amount, is applied as a control voltage to the drive motor 8 via the next digital-to-analog converter 27, the pre-stage amplifier 13, and the drive amplifier 14, thereby controlling the position of the spindle head 1. conduct.

Further, a switching element 28 is connected to the error counter 26 and becomes conductive only when the spindle head 1 is stopped. In other words, this switching element 28 converts the output voltage of the digital-to-analog converter 27 into the hold circuit 30.
The switching element 28 is turned on only when the output of the error counter 26 is at the H level and the command value is at the L level. Therefore, while the spindle head 1 is in motion, the switching element 28 is turned off, but the hold circuit 3o is held by the previously sent signal, and its output voltage is constantly supplied to the electropneumatic converter 31. . The electropneumatic converter 31 controls the diaphragm control valve 24 to a predetermined air pressure based on the control voltage of the hold circuit 3o.

Next, the operation of the embodiment configured as described above will be explained in detail.

When the spindle head 1 is stopped and the position command value is zero, the total load W (N) of the spindle head 1 and the tool 3a
Due to the suspension, a reverse torque acts on the ball screw 7, and the spindle head 1 descends to a point where it is balanced with the output torque of the drive motor 8. That is, a positional deviation amount Δ2 is generated, and this deviation amount is detected by the linear scale 25 and fed back to the error counter 26.

Then, the error output signal of this deviation amount is amplified and acts as a voltage application to the drive motor 8, thereby achieving balance. However, if left as is, problems such as the operating point deviating from the neutral point of the drive amplifier 14 as explained in the conventional example, or a current commensurate with the position deviation amount ΔZ constantly flowing through the drive motor 8 will occur. It is.

Therefore, in the embodiment of the present invention, the positional deviation amount ΔZ is transmitted to the hold circuit 30 through the switching element 28. The relationship between the position deviation amount ΔZ and the control voltage is the second
It is convenient to design with a proportional relationship as shown in the figure. Second
In the figure, the horizontal axis shows the position deviation amount Δ2 (μm), and the vertical axis shows the control voltage (
mV).

The hold circuit 30 has a circuit characteristic of maintaining the output at the previous input data unless updated input data is input, and the output of the hold circuit 30 is connected to the electro-pneumatic converter 31.
, and an output (air pressure) proportional to the input is generated by the electro-pneumatic converter 31. Therefore, the air pressure input to the diaphragm control valve 24 acts on the upper diaphragm 24a, and as a result, the input pressure of the high pressure air source from the compressor 22 is adjusted in a pressure balanced manner to control the output pressure. This output air pressure P
(MPa) acts on the piston 18 and balance force F (F-
P-A) is generated.

In Figure 3, the control voltage (mV) is plotted on the horizontal axis, and the balance force F (
The relationship is shown when N) is plotted on the vertical axis, and as shown in the figure, it is possible to have a nearly linear characteristic with respect to the input control voltage. This balance force F is wire rope 10
As a result, the total load W of the spindle head 1 and the tool 3a is lifted, so the spindle head 1 is lifted and moved upward. Therefore, the positional deviation amount ΔZ becomes smaller, and the load current flowing through the drive motor 8 also decreases. In addition, since the balance force F is also controlled by feeding back the amount of positional deviation, the switching element 28 is turned off when Δz-0 is reached, and the input to the hold circuit 30 is eliminated, so that the pressure P at that time is It will be maintained within the cylinder 17.

The reason why the balance force F is controlled by detecting the positional deviation amount only when the spindle head 1 is stopped is that an accurate balance force is required, and the movement of the spindle head 1 during movement or machining This is due to the fact that the true value of the balance force is unknown when measuring the position at the time.

In addition, the spindle head 1 and the piston 1 in the cylinder 17
The reason why the wire rope 10 connecting between the two parts is formed into a closed loop is that when the piston 18 does not move due to a sudden rise of the spindle head l, for example, the wire rope 10 connects the pulley 1.
There is a risk that the wire rope 10 may come off the track 1, and that the wire rope 10 may be pulled tightly during intense vertical movement.
Since the phenomenon of loosening is repeated, there is a possibility that resonance of the wire rope 10 itself may be induced, which may adversely affect the movement of the spindle head 1. Therefore, it is necessary to eliminate these inconveniences. It is from. As a result, the drive motor 8 is not subjected to any disturbance, and the output torque required for machining can be smoothly controlled. Even if the tool is exchanged with another tool during the process using an electrode exchanger or the like and the amount of the tool changes greatly and the balance goes out of order, the position of the spindle head 1 is detected by the linear scale 25 and the balance force F is controlled. Therefore, balance can be quickly achieved and the current flowing to the drive motor 8 can always be minimized. Furthermore, the tool is light and the cylinder device 1
As described above, even if the balance force F of the spindle head 1 is large and the spindle head 1 is lifted in the child direction, the movement is fed back, so the balance force F is controlled to be small.

[Effect of the invention] According to the present invention, the following effects can be obtained.

■ The load on the spindle head drive motor can be significantly reduced.

■ Since the control operating point can always be located at the neutral point of the drive amplifier, the dynamic range of the drive amplifier (
(Control range) can be used to the maximum extent, and stable control is possible. ■ The mechanical load on the spindle head drive system, such as the ball screw and its support bearings, can be reduced and the service life can be greatly extended. Furthermore, it can be made smaller due to the lower load capacity.

■ Even if the weight of the tool changes, it is controlled using a balance force that corresponds to the suspended weight, so zero point adjustment of the servo system is unnecessary or extremely simple depending on the load.

■ Since the balance force is provided by mechanical force rather than weight, there is no reduction in the mechanical resonance number, and there is no slack in the wire rope, so it can smoothly handle high-speed movement and switching.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an embodiment of the present invention, Fig. 2 is an input/output characteristic diagram of a hold circuit, Fig. 3 is a characteristic diagram of balance force of the device of the present invention, and Fig. 4 is a schematic diagram of a conventional example. It is. 1... Spindle head 3a... Processing tool 4...
・Column 8... Drive motor 10...
Wire rope 13... Full stage amplification section 14... Drive amplification section 16... Cylinder device 24... Diaphragm control valve 25... Position detector 26... Error counter 28... Switching element 30 . . . Hold circuit 31 . . . Electro-pneumatic converter In the drawings, the same reference numerals indicate the same or equivalent parts. Agent Patent Attorney Muneharu Sasaki Figure 1 13: J'1WRY%9 2B: Sui-y'
r>ri'tJFigure 2 Figure 3

Claims (1)

[Claims] A spindle head on which a processing tool is attached, a column on which the spindle head is attached and guides its movement, a drive motor for the spindle head, a cylinder device connected to the spindle head by a wire rope forming a closed loop, and the cylinder. a control valve that controls pressure supplied to the device; a position detector for the spindle head; an error counter that subtracts a detection value detected by the position detector from a preset command value; and the error counter. a control circuit that controls the drive motor of the spindle head based on the output of the counter; a switching element that becomes conductive only when the spindle head is stopped; and a control circuit that controls the drive motor of the spindle head based on the output of the error counter via the switching element. A spindle head balance device characterized by comprising a hold circuit that operates to control pressure with respect to a valve.