JPH068090A - Magnet chuck device and control method thereof - Google Patents

Abstract

PURPOSE:To hold the density of magnetic flux, generated in a magnet chuck coil, always constant so as to maintain chucking force in the steady state by providing an error correcting circuit for comparing the actual current value with the reference current value so as to correct electricity flowing in the mag net chuck coil on the basis of the error. CONSTITUTION:A workpiece is chucked to a main spindle by electromagnetic force generated in a magnet chuck coil 6. The change of a current flowing in the magnet chuck coil 6 is detected by a current detecting circuit 15. The actual current value detected by the current detecting circuit 15 and fed back is compared with the reference current value selected by an external command setting circuit 19. On the basis of this error, the current flowing in the magnet chuck coil 6 is corrected by an error correcting circuit 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnet chuck device and a control method therefor, and more particularly, to a magnet chuck device for chucking a workpiece on a spindle by an electromagnetic force generated in a magnet chuck coil, and the magnet chuck. The present invention relates to a control method for controlling a chucking force in an apparatus according to a work piece.

[0002]

2. Description of the Related Art For example, in the case of grinding a groove of an annular work such as a bearing inner ring, a magnet chuck device is used as a means for positioning and supporting a work being the annular work with respect to a grinding wheel. It is common to do.

A magnet chuck device used in this type of grinding machine has a structure in which a workpiece is chucked on a spindle by an electromagnetic force generated in a magnet chuck coil. The electromagnetic force of the magnet chuck coil is set so as to be an appropriate chuck force depending on the size of the workpiece and the grinding processing conditions.

The control of the chucking force by the magnet chuck coil has been performed by varying the current supplied to the magnet chuck coil based on a voltage supply circuit using a transformer or a slider.

That is, when a transformer is used, the supply voltage is changed by switching the taps on the secondary side of the transformer, and the current flowing through the magnet chuck coil is adjusted. In this case, by varying the sliding position of the built-in winding, the supply voltage is set to the desired value, and the chucking force of the magnet chuck coil is controlled to the optimum value. ing.

[0006]

By the way, the conventional magnet chuck device has the following problems in using the transformer and the slider as described above.

First, in the case of using a transformer, when changing the current supplied to the magnet chuck coil, it is necessary to select and switch the tap on the secondary side of the transformer. Usually, the tap of the transformer is a bolt. Since it is fixed with nuts or soldering, it is impossible to switch while keeping the energized state, and there is a problem that the non-energized state intervenes in tap switching. Further, in the actual situation, this tap switching can obtain only a stepwise voltage change.

In this respect, when the slidac is used,
This is effective because it is possible to continuously change the voltage supplied to the magnet chuck coil. However, commercially available slideracs generally have a structure in which the dial is manually rotated when the current supplied to the magnet chuck coil is changed, so that the chucking force on the workpiece is reduced to that grinding state. It is very difficult to continuously change it in accordance with the above. Especially, during finish grinding or spark-out grinding, the chucking force is weakened, and the distortion of the work piece generated during rough grinding is restored to the original state. However, it was difficult to set the chucking force at this time to the optimum value. Further, in this case, if it is attempted to change the current to the magnet chuck coil by following the change, it is necessary to provide a driving mechanism such as a motor for automatically rotating the dial from the outside, which is a large scale. There was a problem that equipment was needed.

In addition to the above problem, the temperature of the winding of the magnet chuck coil rises due to the heat generation of the magnet chuck coil and the heat generation of the work piece due to the friction with the grinding stone. The resistance value increases.
As a result, the value of the current flowing through the magnet chuck coil decreases, and the magnetic flux density generated due to the decrease in the current decreases. As described above, when the magnetic flux density in the magnet chuck coil is reduced, the chucking force is reduced accordingly, and it becomes difficult to properly hold the workpiece.

In order to prevent this from happening, it is possible to assume in advance that the magnetic flux density will be small, and there can be considered a means for setting the current supplied to the magnet chuck coil to a large extent, but during machining of the workpiece. , The chuck force changes due to the change in the magnetic flux density due to the decrease in the current value, and the balance between the chuck force and the force that assists the workpiece is lost, and the spindle rotates, There is a problem that it is still difficult to stop the rotation of the work piece or keep the work piece properly by rotating around the grinding wheel.

Therefore, the present invention has been proposed in view of the above problems, and an object of the present invention is to change the chucking force for a workpiece continuously and continuously with a simple structure. At the same time, it is an object of the present invention to provide a magnet chuck device and a control method thereof that can always keep the magnetic flux density generated therein constant even if the temperature of the magnet chuck coil changes.

[0012]

As a technical means for achieving the above object, a magnet chuck device of the present invention is a magnet chuck for chucking a workpiece on a spindle by an electromagnetic force generated in a magnet chuck coil. In the device, an external command according to the processing conditions, an external command setting circuit that selects and sets a desired current value from a plurality of reference current values, a current detection circuit that detects a change in the current flowing through the magnet chuck coil, An error correction circuit that compares the actual current value detected and fed back by the current detection circuit with the reference current value selected by the external command setting circuit and corrects the current flowing through the magnet chuck coil based on the error. It is characterized by having.

In the magnet chuck device, in addition to the external command setting circuit, the current detection circuit, and the error correction circuit, when the workpiece is unchucked, the reverse excitation current and the current are applied depending on the size of the workpiece. A degaussing control circuit that degausses the workpiece and the supporting portion of the workpiece by changing the time,
It is desirable to provide an abnormality detection circuit that detects an abnormal state of the magnet chuck coil.

Further, the method of controlling the magnet chuck device of the present invention, depending on the processing conditions of the workpiece when the workpiece is machined in a state of being chucked to the main shaft by the electromagnetic force generated in the magnet chuck coil. An external command selects a desired current value from a plurality of reference current values, while detecting a change in the current flowing through the magnet chuck coil, comparing the selected reference current value with the detected actual current value, It is characterized in that the current flowing through the magnet chuck coil is corrected based on the error obtained from the comparison result.

[0015]

In the present invention, the current supplied to the magnet chuck coil is constantly monitored and feedback-controlled so that the current value is kept constant and the magnetic flux density generated in the magnet chuck coil is kept constant. Further, the chucking force for the work piece can be continuously changed in a stepless manner according to the situation based on the external command, and the chucking force is always set to the optimum state.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a magnet chuck device and its control method according to the present invention will be described with reference to FIGS.
1 shows an example of a circuit configuration of the magnet chuck device, and FIG. 2 shows an example of a concrete structure of the magnet chuck device of the grinder.

First, the magnet chuck device shown in FIG. 2 grinds a magnetic workpiece (1), which is an annular work, such as a bearing inner ring, by grinding a groove of the workpiece (1). Position and support the grinding wheel (2).

This magnet chuck device has a main shaft (4) consisting of a rear rotary shaft (3b) and a front rotary shaft (3a) mechanically attached to the tip of the rear rotary shaft (3b),
A backing plate (5) is mechanically and coaxially connected to the tip of the front rotary shaft (3a). At the tip of the backing plate (5), the end surface of the workpiece (1) to be positioned with respect to the grinding wheel (2) is chucked by an electromagnetic force by a magnet chuck coil described later. A magnet chuck coil (6) is arranged around the front rotary shaft (3a) of the main shaft (4) so as to surround the front rotary shaft (3a). This magnet chuck coil (6) is attached to a base (8) via a flux guide (7), and a plurality of shoes (10) are attached to the base (8) via shoe brackets (9). These shoes (10)
Of the workpiece chucked to the grinding wheel (2) by the backing plate (5) by bringing the backing plate (5) into contact with the groove or outer diameter of the workpiece (1) chucked on the backing plate (5) Support (1) as a supplement.

Among the components of the magnet chuck device, the front rotary shaft (3a), the flux guide (7),
The base (8), the shoe bracket (9), the shoe (10) and the backing plate (5) are made of a magnetic material, and the electromagnetic force of the magnet chuck coil (6) is made by these constituent members and the work piece (1). This forms a closed magnetic path through which the magnetic flux passes, and the workpiece (1) is chucked to the backing plate (5) by magnetic attraction. On the other hand, the rear rotary shaft (3b) is made of a non-magnetic material so that the magnetic flux does not escape to the rear.

During the grinding of the work piece (1), the work piece (1) chucked by the backing plate (5) is actuated by the spindle (4) while being supported by the shoe (10). The grinding wheel (2), which is rotated by this, rotates the workpiece (1) based on a predetermined grinding power [tangential direction grinding force affected by the sharpness of the wheel].

Next, the constituent circuits of the magnet chuck device, which is a feature of the present invention, will be described.

As shown in FIG. 1, the main part of this magnet chuck device is composed of a chuck coil exciting circuit (11) connected to a magnet chuck coil (6).
The chuck coil excitation circuit (11) includes an excitation control circuit (12), a forward / reverse switching circuit (13), a power circuit (14), a current detection circuit (15), an error correction circuit (16) and a demagnetization control circuit (17). ) Consists of. This chuck coil excitation circuit (1
In addition to 1), rectifying and smoothing circuit (18), external command setting circuit (1
9), a regeneration control circuit (20) and an abnormality detection circuit (21) are provided.

Specifically, the rectifying / smoothing circuit (18) is composed of a circuit element including a capacitor, and rectifies and smoothes an AC input current and sends a DC output current.

The excitation control circuit (12) of the chuck coil excitation circuit (11) controls the direct current output from the rectifying / smoothing circuit (18) as the excitation current of the magnet chuck coil (6). The forward / reverse switching circuit (13) switches the direction of the exciting current output from the excitation control circuit (12). That is, when the workpiece (1) is chucked, the magnet chuck coil (6) is positively excited, and when the workpiece (1) is unchucked, the magnet chuck coil (6) is reversely excited. The power circuit (14) supplies an exciting current output from the excitation control circuit (12) to the magnet chuck coil (6) via the forward / reverse switching circuit (13). The current detection circuit (15) is connected between the power circuit (14) and the magnet chuck coil (6) and detects an exciting current flowing through the magnet chuck coil (6).

On the other hand, the external command setting circuit (19) uses, for example, an external input from a sequencer or digital switch to
The desired current value corresponding to the grinding power is set so as to follow the change in the grinding power, and the set value that serves as the reference for the strength of the positive excitation and the reverse excitation is stored and retained, and the reference current value is used for the chuck coil excitation. It is sent to the circuit (11).

The magnet chuck exciting circuit (11)
The error correction circuit (16) is a current value fed back from the current detection circuit (15), that is, the current value actually flowing in the magnet chuck coil (6) and the reference current value from the external command setting circuit (19). Is compared, the error between the actual current value and the reference current value is corrected, and the corrected current value is sent to the excitation control circuit (12).

The demagnetization control circuit (17) further includes a backing plate (5) and a work piece according to the size of the work piece (1) and the like, based on a control signal and a reverse excitation magnetic force setting signal described later. Execute the optimum demagnetization in (1). Excitation ON-OFF input from an external sequencer etc. for the control signal
There are signals, forward / reverse switching signals, and strong / weak switching signals.
Further, the reverse excitation magnetic force setting signal is applied to the magnet chuck coil (6) when the magnet chuck coil (6) is reversely excited.
It is a signal that sets the reverse excitation current and the time that flow to the desired value.

Next, the regeneration control circuit (20) is connected between the power circuit (14) and the rectifying / smoothing circuit (18) and operates based on the gate control signal from the excitation control circuit (12). By the way, when the exciting current supplied to the magnet chuck coil (6) is cut off by the excitation OFF signal, it is possible to prevent the energy accumulated in the magnet chuck coil (6) from changing due to self-induction when the exciting current is supplied. A back electromotive force is generated. Therefore, in this regenerative control circuit (20), a gate control signal is sent from the excitation control circuit (12) when the exciting current is cut off, and the counter electromotive force generated in the magnet chuck coil (6) by the gate control signal. Is made zero by the series circuit of the capacitor of the rectifying and smoothing circuit (18) and the inductance of the magnet chuck coil (6).

Finally, the abnormality detection circuit (21) detects an abnormal state such as a breakage of the magnet chuck coil (6), the occurrence of a rare short circuit and the occurrence of an overcurrent. Stop the grinding machine and perform maintenance of the magnet chuck coil (6).

The circuit operation of the magnet chuck device having the above circuit configuration will be described below.

First, when the workpiece (1) is mounted on the backing plate (5) of the magnet chuck device, the forward / reverse switching circuit (13) is set to a positive excitation state by a control signal, and an alternating input current is applied. The rectifying / smoothing circuit (18) converts it into a direct current, and the direct current is controlled by the excitation control circuit (12) as an exciting current. The exciting current is passed through the forward / reverse switching circuit (13) and the power circuit (14). Supply to the magnet chuck coil (6). At this time, the positive excitation current flowing through the magnet chuck coil (6) is detected by the current detection circuit (15) as indicated by the solid arrow in the figure.

On the other hand, in the external command setting circuit (19), the reference current value set by an external input such as a sequencer or a digital switch is fed to the magnet chuck coil (6) and fed back from the current detection circuit (15). It is input to the error correction circuit (16) together with the actual current value. The error correction circuit (16) compares the reference current value with the actual current value, corrects the error between them, and sends the corrected current value to the excitation control circuit (12). By feeding back this current value, even if there is a temperature change in the magnet chuck coil (6), the current flowing through it can be kept constant, and the magnetic flux density generated in the magnet chuck coil (6) can be kept constant. it can. If the external input from the external command setting circuit (19) sets a desired current value corresponding to the grinding power so as to follow the change of the grinding power, for example, the magnet chuck coil (6 ), The value of the current flowing through the) always matches the desired current value corresponding to the grinding power described above, and as a result, the chucking force of the backing plate (5) on the workpiece (1) is
It is possible to always maintain a good condition by following changes in the grinding power.

When the predetermined grinding is completed on the work piece (1) as described above, the work piece (1) is separated from the backing plate (5). It is necessary to demagnetize 1) and the backing plate (5).

When removing the workpiece (1) from the backing plate (5), the demagnetization control circuit (17) is activated by the control signal and the forward / reverse switching circuit (1) is operated.
Set 3) to the reverse excitation state. At this time, a counter electromotive force is generated in the magnet chuck coil (6) by cutting off the positive excitation current. This counter electromotive force is regenerated by the gate control signal via the power circuit (14). By the circuit (20), it becomes zero in a short time due to the time constant in the series circuit of the capacitor of the rectifying and smoothing circuit (18) and the inductance of the magnet chuck coil (6).

Further, the reverse excitation magnetic force setting signal is used to set the reverse excitation current flowing through the magnet chuck coil (6) and time to desired values, and the reverse excitation current is supplied from the excitation control circuit (12) via the demagnetization control circuit (17). A current is supplied to the magnet chuck coil (6) via the forward / reverse switching circuit (13) and the power circuit (14). This magnet chuck coil (6)
Backing plate (5) due to reverse excitation current flowing in
And the residual magnetism existing in the work piece (1) is reduced as much as possible, and both are demagnetized.

The magnet chuck coil (6)
When a wire breakage, a rare short circuit occurs, or an overcurrent occurs, the abnormality detection circuit (21) detects these abnormal states and informs the operator of the abnormal state based on the detection output. As a result, the operator can quickly replace the defective magnet chuck coil (6) with a new one and prevent the occurrence of a defect.

[0037]

According to the present invention, by constantly monitoring the current supplied to the magnet chuck coil and performing feedback control, the current value is kept constant even if the temperature of the magnet chuck coil changes. The magnetic flux density generated in the chuck coil can be kept constant, and the chucking force on the workpiece can be maintained in a steady state. Also, based on the external command,
The chucking force can be continuously changed continuously according to the situation, and the chucking force can be always set to the optimum state.

[Brief description of drawings]

FIG. 1 is a configuration circuit diagram showing an embodiment of a magnet chuck device according to the present invention.

FIG. 2A is a cross-sectional view showing a magnet chuck device of the present invention used for a grinding machine, and FIG. 2B is a side view showing a workpiece supported by a shoe and a grinding wheel provided for the workpiece.

[Explanation of symbols]

 1 Workpiece 4 Spindle 6 Magnet chuck coil 15 Current detection circuit 16 Error correction circuit 19 External command setting circuit

Claims (4)

[Claims] 1. A magnet chuck device for chucking a work piece on a spindle by an electromagnetic force generated by a magnet chuck coil, wherein a desired current value is selected from a plurality of reference current values by an external command according to processing conditions. The external command setting circuit set by the above, the current detection circuit that detects changes in the current flowing in the magnet chuck coil, the actual current value detected and fed back by the current detection circuit, and the reference selected by the external command setting circuit. A magnet chuck device comprising: an error correction circuit that compares a current value and corrects a current flowing through the magnet chuck coil based on the error. 2. When the workpiece is unchucked, the reverse excitation current and the energization time are varied according to the size of the workpiece,
2. The magnet chuck device according to claim 1, further comprising a degaussing control circuit for degaussing the workpiece and a supporting portion of the workpiece. 3. The magnet chuck device according to claim 1, further comprising an abnormality detection circuit for detecting an abnormal state of the magnet chuck coil. 4. When machining a workpiece in a state in which it is chucked on a spindle by an electromagnetic force generated by a magnet chuck coil, a plurality of reference current values are desired by an external command according to the machining conditions of the workpiece. While selecting the current value of, the change in the current flowing through the magnet chuck coil is detected, and the selected reference current value and the detected actual current value are compared,
A method of controlling a magnet chuck device, wherein a current flowing through a magnet chuck coil is corrected based on an error obtained from the comparison result.