JPH0330885B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a backcrush amount measuring device, and more particularly to a backcrush amount measuring device that improves the positioning accuracy of a precision machine tool using backcrush or dead zone.

With recent remarkable advances in electronics technology and electronic control technology for machines, numerical control (hereinafter abbreviated as NC) for machine tools has become commonplace, realizing unmanned operation and labor savings, as well as improving machining accuracy. This has improved by nearly an order of magnitude compared to before machines were numerically controlled. Therefore, the machining accuracy currently required is micron level, and even the slightest play or deviation of the machine cannot be tolerated.

Figure 1 shows an overview of a typical NC machine tool. In FIG. 1, the table designated by reference numeral 10 is a known X, Y cross table, and the two upper and lower tables 10a and 10b are X, Y cross tables in the illustrated example.
Although they are relatively movable in the axial direction, they are configured to move together in the Y-axis direction. These upper and lower tables 10a and 10b have nuts 14 that screw together ball screws 12a and 12b.
a, 14b, bearings 18a, 1 that support guide rods 16a, 16b parallel to the ball screws;
8b are provided separately and independently. Each of the ball screws 12a and 12b is directed to the nuts 14a and 14b so as to move the upper table 10a in the X-axis direction and to move the lower table 10b (including the upper table as one) in the Y-axis direction. are screwed together. Gears 20a, 20b provided on each ball screw 12a, 12b are driven by a drive motor 22a,
The output shafts 22b mesh with gears 26a, 26b provided on the output shafts 24a, 24b, respectively, and the output shafts have rotation angle detectors (rotary encoders) 28a,
28b is attached. A main shaft 32 is provided above the cross table 10 and is supported by a support arm 30 so as to be movable back and forth, and a tool 36 for cutting a workpiece 34 is attached to the main shaft 32.

The NC device 40 outputs a command pulse signal for machining, and the output signal from its output terminal 40a is supplied to a positioning control circuit 42, and the output signal of this positioning control circuit 42 is transmitted via the amplifier circuit 44 to the above-mentioned The signal is supplied to the drive motor 22a, and the output signal of the rotation angle detector 28a is supplied to the positioning control circuit 42. The output signal from the output terminal 40b of the NC device 40 is transmitted to the unit 4 including the positioning control circuit and amplifier circuit.
6 to the drive motor 22b, and the output signal of the rotation angle detector 28b is supplied to the unit 46 through a circuit (not shown).

The NC machine tool has the above configuration, and its operation will be explained below. When the drive motor 22a is driven based on a command pulse signal (programmed in advance on the memory tape 48) issued from the NC device 40, the speed is reduced by the ratio of the number of teeth between the gear 26a and the gear 20a. The driving force of the drive motor is transmitted to the ball screw 12a. When the ball screw 12a rotates, the upper table 10a moves in the X-axis direction because the nut 14a is fixed. This movement is caused by a guide rod 16a supported by a bearing 18a.
is arranged in parallel with the ball screw 12a, so this is done smoothly.

The amount of rotation of the output shaft 24a of the drive motor 22a, that is, the amount of movement of the upper table 10a, is detected by the rotation angle detector 28a, and this detection signal is fed back to the positioning control circuit 42 to control the position of the upper table 10a. It will be done.

The lower table 10b is also similar to the above, and the drive motor 22b - output shaft 24b - gear 2 is operated based on the command pulse issued from the NC device 40.
The lower table (also integrated with the upper table) 10b is controlled to a predetermined position in the Y-axis direction via 6b-gear 20b-ball screw 12a.

While moving the cross table 10 in the X-axis direction and the Y-axis direction as described above, the main shaft 32 is moved up and down by the command pulse signal issued from the NC device 40 to move the workpiece 36 on the table to a desired position. It is cut into a shape.

In the above NC machine tools, gear 20
There is play between a and 26a and play between the ball screw 12a and the nut 14a, and it is extremely difficult to eliminate this play. The above-mentioned backlash (referred to as backlash) is expressed as ΔX ₁ in the relationship between the displacement X _n of the drive motor 22a and the actual position X of the upper table 10a, as shown in FIG.

Further, in the relationship between the input voltage Ex of the drive motor 22a and _{the rotational speed Vx ,} as shown in FIG. 3, there exists an amount ΔE at which the drive motor 22a does not start moving even if a voltage is applied. In automatic control engineering, the above amount is called the dead zone. The magnitude of this amount varies depending on the table load and the frictional force between the guide rod 16a and the bearing 18a, but in general, in a position servo system, when it is processed as a voltage corresponding to the position, it is divided by the gain K of the amplifier circuit 44. This value corresponds to the position error ΔX ₂ =ΔE/K, and therefore this value is affected by the load of the drive motor 22a and the gain K of the amplifier circuit 44.

Figure 4 shows the relationship between the feed command value Xc and the actual movement X when the machine is actually moved under the above-mentioned mechanical backlash and electrical dead zone. , mechanical play ΔX ₁
The sum value ΔX _B is the value ΔX ₂ obtained by converting the dead zone ΔE into a position error. That is, it can be expressed by the following equations: ΔX _B =ΔX ₁ +ΔX ₂ (1) ΔX ₂ =ΔE/K (2). Generally, when measuring the accuracy of a machine, it is difficult to measure ΔX ₁ and ΔX ₂ separately, so ΔX _B is often measured and used as the backlash amount of the machine.

NC machine tools are usually equipped with a backlash correction device, which stores the pre-measured value of ΔX _B as correction data, and during actual positioning, the command value plus ΔX _B is added every time the direction of movement is changed. I output it to avoid errors.

However, the above value of ΔX _B changes due to the aging of mechanical play (change in ΔX ₁ ), changes in frictional force, and fluctuations in the gain of the amplifier circuit (change in ΔX ₂ ). This is not a value that can be treated as a constant correction amount over time. Furthermore, measurement of the value requires a highly accurate measuring instrument, and re-correction is extremely difficult.

The present invention has been made in view of the above-mentioned conventional problem, and its purpose is to easily and automatically measure the backlash amount using the machine tool itself, without using a special backlash amount measuring device. An object of the present invention is to provide a backlash amount measuring device that measures a backlash amount ΔX _B.

In order to achieve the above object, the present invention provides a moving body configured to hold a workpiece and move it in a desired direction, a drive motor that drives the moving body in at least one axial direction, and a drive motor for driving the moving body in at least one axis direction. A fixed body disposed above the moving body to face the moving body, an electrode attached to the fixed body via an insulator, and a predetermined voltage applied between the electrode and the workpiece, A comparator circuit that sets a voltage level to detect contact and separation between the workpiece and the electrode caused by movement compares the drive command value with a preset reference voltage level. The apparatus comprises an electrical detection means for outputting an output, and a backlash amount detection circuit that uses a drive command value given to the drive motor from the contact between the workpiece and the electrode detected by the electrical detection means as the backlash amount. Features.

Hereinafter, preferred embodiments of the present invention will be described based on the drawings. FIG. 5 is a circuit diagram of the backlash amount measuring device of the present invention. The electrode 50 is an insulator 5
It is attached to the main shaft 32 via 2. A charging/discharging capacitor C ₁ is connected in parallel to this electrode 50 and the workpiece 34 as a measurement object fixed on the upper table 10 a, and a voltage Eo of 40 V or less is connected to this charging/discharging capacitor via a resistor ₁ . A low-voltage power supply 54 is connected. The comparator 54 is an electrical detection means for detecting contact between the electrode 50 and the workpiece 34 and determining separation between the electrode 50 and the workpiece 34. The positive terminal of the charging/discharging capacitor is connected to the inverting input terminal of the comparator 56, and the non-inverting input terminal of the comparator 56 is connected to a power source 58 that supplies a reference voltage V _r via a resistor R ₃ . Also, the non-inverting input terminal and output terminal of the above comparator are resistors.
A lamp 62 having one end connected to a voltage +V supply terminal 60, a series circuit of a resistor _R2 and a capacitor _C2 , and an AND gate 64 are connected to the output terminal through _R4 . A connection point P between the resistor R ₂ and the capacitor C ₂ is connected to the other input terminal of the AND gate 64 via an inverter 80 .

In the present invention, the backlash amount measuring circuit has the above circuit configuration, and its operation will be explained below. As described above, the drive motor 22a is driven to move the upper table 10a in the X-axis direction (in the direction of the arrow in FIGS. 1 and 5), and the workpiece 34 and the electrode 50 are brought into contact with each other or approached to a very narrow distance. Then, the voltage V _p between the workpiece 34 and the electrode 50 (hereinafter referred to as the electrode gap) decreases, and the charging/discharging capacitor
The electrical energy stored in C ₀ is released,
A single discharge occurs, and the contact point between the workpiece 34 and the electrode 50 is maintained in contact. Therefore, the comparator 56 turns on the lamp 62 when the electrode voltage V _p becomes lower than the reference voltage V _r . At this point in time, the current position display of the single NO device 40 is preset to zero, and the upper table 10a is moved in the opposite direction to the above-mentioned moving direction. In this case, the contact between the workpiece 34 and the electrode 50 is not released during the backlash section, so the interelectrode voltage V _p remains zero.
As soon as the contact is released, the voltage between electrodes V _p exceeds the reference voltage V _r . At this time, comparator 5
The output of No. 6 rises, and the rising differential circuit composed of the resistor R ₂ , the capacitor C ₂ , the inverter 66, and the AND gate 64 generates a stop interrupt to the NC device 40, and the feed of the upper table 10a is immediately started. to stop. The position of this stop is the amount of backlash, which is a combined value of backlash and dead zone.

In the above embodiment circuit, in order to improve the detection accuracy, the comparator 56 is equipped with hysteresis resistors R ₃ and R ₄ , and when the voltage between electrodes V _p decreases, as shown in FIG. 6, which will be described later, It reaches a relatively high value V ₁ and rises again to a lower voltage V ₂
is based on.

FIG. 6 is a time chart of the circuit shown in FIG. 5, in which _S1 is the comparator 56.
output, S ₂ is the rising differential output, +X _p is the workpiece 3
-X _p is the stepping pulse when the table is sent in the direction of contacting the electrode 50 with the workpiece 3.
This is a step pulse when the table is moved in the direction of opening from 4.

Note that in the above embodiment, a voltage is applied between the electrode and the workpiece to detect contact between the two, but it is not possible to detect contact between the electrode and the workpiece, but it is possible to detect the contact between the electrode and the workpiece. In the case of a machine tool such as the one shown in FIG. Furthermore, the tool electrode itself can be used in place of the electrode, which is very convenient in practice.

The above description describes the measurement of the amount of backlash in the X-axis direction by moving the upper table 10a.
The amount of backlash in the Y-axis direction for moving the lower table 10b can also be measured in the same manner as described above.

As described above, since the present invention detects and measures the backlash amount ΔX _1B easily and automatically using the machine itself, there is no need to prepare a special high-precision backlash amount measuring device. Also,
Even if the amount of backlash changes due to aging of the machine, changes in frictional force, etc., the effect is that the amount of backlash after the change can be detected accurately. Therefore, by applying the device of the present invention to an NC device, it is possible to accurately correct the amount of backlash set in the positioning control system of the machine, and it is possible to improve machining accuracy through high-precision positioning. can.

[Brief explanation of drawings]

Figure 1 is a perspective view showing an overview of the NC machine tool, Figure 2 is a relationship between the amount of backlash generated on the table and the momentum of the table feed motor, Figure 3 is a diagram showing the dead zone of the motor, and Figure 4 is A diagram showing the situation when the backlash amount and the dead zone are combined, FIG. 5 is a circuit configuration diagram showing one embodiment of the backlash amount measuring device of the present invention, and FIG.
FIG. 3 is a time chart showing the electrical operation of the measurement circuit shown in the figure in response to the passage of time. In each figure, the same members are given the same symbols, 10 is an X, Y cross table, 12a, 12b are ball screws, 14a, 14b are nuts, 16a, 16b
is a guide rod, 18a, 18b are bearings, 20
a, 20b are gears, 22a, 22b are drive motors, 24a, 24b are output shafts, 26a, 26b are gears, 28a, 28b are rotation angle detectors, 30 is a support arm, 32 is a main shaft, 34 is a workpiece, 36 is a tool, 40 is an NC device, 50 is an electrode, 52 is an insulator, 54 is a low voltage power supply, 56 is a comparator, 58
is a power supply, 62 is a lamp, 64 is an and gate, 6
6 is an inverter, R ₁ to R ₄ are resistors, and C ₁ and C ₂ are capacitors.

Claims (1)

[Claims] 1. A movable body configured to hold a workpiece and move in a desired direction, a drive motor that drives this movable body in at least one axial direction, and a fixing member disposed above the movable body and facing the movable body. A predetermined voltage is applied between the body, an electrode attached to the fixed body via an insulator, and the electrode and the workpiece, and the workpiece and the workpiece generated by the movement of the movable body are an electrical detection means that outputs a drive command value by comparing it with a preset reference voltage level using a comparison circuit that sets a voltage level to detect contact and separation with the electrode; A backlash amount measuring device comprising: a backlash amount detection circuit that uses a drive command value given to the drive motor from the contact between the workpiece and the electrode detected by the means as the backlash amount.