JPH0219933Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a control device for attaching and demagnetizing a permanent magnetic chuck, and in particular, it is used as an adsorption holder when machining ferromagnetic metals such as iron plates. It is a control device for

Conventionally, in order to demagnetize a permanent magnetic chuck with a device for attaching and demagnetizing a chuck, DC pulses are repeatedly applied to the chuck coil in the order of negative and positive poles in a rectangular waveform or sawtooth waveform, and the pulse value is also changed for each pulse. A so-called direct current pulse demagnetization method was generally employed in which demagnetization is completed by attenuation. However, in this type of demagnetization method, in reality, the dial is manually rotated one step at a time to close the negative and positive electrical contacts alternately to attenuate the pulse, whereas the automatic method uses a mechanical cam mechanism directly connected to the motor. The pulse is attenuated by sequentially pressing and closing these electrical contacts. Therefore, there are disadvantages in that demagnetization takes time and the mechanical parts are bulky, making the device expensive.

Taking these points into consideration, this invention demagnetizes the chuck by applying a reverse excitation current to the chuck coil, which allows magnetization and demagnetization to be performed in one shot, that is, with a single switch operation. The present invention provides a device that can complete the process, and uses a constant current as the reverse excitation current to ensure smooth release of the magnetized object at all times. That is, this idea provides a switch to change the excitation direction of the demagnetizing coil, and in particular, when demagnetizing, a triax is provided on the AC side of the rectifier circuit, while a current detection resistor and current limiter are connected in series to the excitation coil on the DC side. The AC phase control of the triax is performed using the voltage detected by the resistor, and the ratio of these two resistors is appropriately selected so that a range with good linearity is selected as the operating point during AC phase control. .

An embodiment of this invention will be described with reference to the figures. 1st
The figure shows a general permanent magnet type chuck, in which a permanent magnet 3 is arranged in the center of an iron box 1, and a detachable magnet coil 4 is wound around it. In addition, 2 is a suction plate, 5 is a magnetic pole, and 6 is an object to be magnetically attached to the workpiece to be set. FIG. 2 is a wiring diagram of a control circuit for attaching and demagnetizing a permanent magnetic chuck according to this invention, and FIG. 3 is a wiring diagram of a gate circuit for controlling an identification current. First, in Figure 2, 4 is the first
In the magnetizing/demagnetizing coil shown in the figure, if the polarity changeover switch normally located at the neutral position N is positive from both terminals, the first ON contact of the cam switch CS
The DC output terminals _7a , 7b of the diode bridge 7 are connected to the DC output terminals _7a , 7b of the diode bridge 7 through the CS _1a and the second on contact CS 2a, and in the negative case through the first off contact CS _1b and the second off contact CS 2b.
are connected to each other. In addition, the second switching off contact
An exciting current detection resistor R 2 and a current control resistor R ₁ are connected between CS _2b and the negative terminal 7b of the diode bridge 7 _.
are inserted in series. On the other hand, the AC input side terminal 7c of the diode bridge 7 is connected to one end of the third switching ON contact CS _3a of the cam switch CS and the third switching OFF contact of the cam switch CS which is connected to the triax 8.
The terminal _7d is connected to one end of the contact tm of the time switch TM.
Furthermore, the third switching on contact CS _3a of the cam switch CS
The other end and the other end of CS _3b are the same fourth switching ON contact.
One end of each of CS _4a and ON contact CS _4b is connected to one end of the timer TM, and the other end of the timer TM is connected to one end of the power source E together with the other end of the contact tm. Further, the other ends of the fourth switching ON contact CS _4a and the switching OFF contact CS _4b are both connected to the other end of the power source E. Note that switches S ₁ and S ₂ are power switches. 9 is a gate circuit for constant _current control, the contents of which are shown in FIG. and gate terminals are connected to 9d, 9f and 9c. or,
VR is a variable resistor connected to terminals 9p, 9q, and 9r with a reference voltage or demagnetizing current setting device.

Next, the contents of the constant current control gate circuit 9 are shown in FIG. 3, and the main components are 10 a DC amplifier, 11 a UJT, and 12p a B ₂ of the UJT 11.
Primary winding of the transformer connected to the electrode terminals, 12S
is the same secondary winding and is connected to terminals 9c and 9d in FIG. Thus, to explain the circuit operation of FIGS. 2 and 3, a timer TM is connected to the power source E in addition to the power switches S ₁ and S ₂ , and by setting the time of the timer TM in advance, , by turning on power switches S ₁ and S ₂ , the power supply voltage changes to the timer.
According to TM, when the set time comes, contact TM is turned on and the circuit is ready for operation. Therefore cam switch
CS from neutral position N to ON (magnetized) side, that is, CS _1a ,
When switched to CS _2a , CS _3a , and CS _4a , the AC power source E does not pass through the triax 8, but is directly full-wave rectified by the diode bridge 7, and then is given positive excitation as the magnetizing coil 4. The power-on time during this time is determined by a timer.
In one practical example, TM is set to complete the process by applying electricity for about 3 seconds. Next cam switch CS
When switched from the neutral position N to the off (demagnetized) side, that is, reverse excitation, each cam switching contact CS _1b , CS _2b , CS _3b ,
The AC power supply E is switched to CS _4b , passes through triax 8, is converted to DC voltage by diode bridge 7, and is taken out, passing through terminal 7a, contact CS _1b , demagnetizing coil 4, contact CS _2b , and then resistor R _2. , _R1 are sequentially applied to the terminal 7b, and the demagnetizing coil 4 is reversely excited. As shown in Figure 3, a resistor R ₃ , a diode D ₄ ,
A circuit configuration of D ₅ and capacitor C ₁ can be adopted for the power supply. The reverse excitation current at this time is preset to approximately 1/3 to 1/4 of the forward excitation current during magnetization due to the presence of resistors R ₁ and R ₂ , and the voltage drop across resistor R ₂ is the same as that at terminals 9a and 9b. The signal is taken out and applied to one input terminal of the DC (feedback) amplifier 10 shown in FIG.
On the other hand, the reference voltage set by the variable resistor VR (which determines the reverse excitation current) is set at terminals 9p, 9q, and 9r, taken out, and applied to the + input terminal of the DC amplifier circuit 10. It is compared in phase with the voltage across the detection resistor R ₂ applied to the same input terminal, that is, the voltage between terminals 9a and 9b. This differential voltage is amplified by a DC (feedback) amplifier 10, taken out, and passed through resistor R ₃ diode D ₁ to UJT 1.
It is added to 1 emitsuta. The increase or decrease in current generated in this way is taken out to the primary winding 12p of the transformer through the _B2 electrode of the UJT 11, applied to the secondary winding 12s, and applied between the gate cathode of the triax 8 from terminals 9c and 9d. It is possible to control the advance of the phase shift, that is, increase in output, or the delay of phase shift, that is, decrease in output, in synchronization with the alternating current voltage, thereby providing negative feedback so that the output current is always kept constant. Therefore, it is possible to always supply a stable DC current despite fluctuations in input voltage and temperature changes in load coil resistance. In addition, the aforementioned DC stabilization operation is instantaneously performed by electrical non-contact control, and when the permanent magnet is demagnetized, the contact TM opens approximately 3 seconds after the coil is energized based on the time setting of the timer TM. Even if the cam switch is not returned to the intermediate position, the cam switch is held and energized, and the magnetized object 6 can always be smoothly released from the permanent magnet chuck.

Thereafter, by returning the cam switch to the neutral position N, all circuits are turned off and the timer TM is also reset. The test results based on this invention are as follows: -10% input for set current 1.5A/2.0A/2.5A for input voltage 100V coil fluctuation ±10% -0.5% + 10% input -0.5% + 10% input hour +0.67
% was obtained and complete demagnetization was performed.

As described above, this invention uses a triax for AC phase control to make it possible to reduce the size and weight, and also selects the ratio of the current detection resistor R ₂ and current limiting resistor R ₁ to about 1:5 to achieve a straight line during AC phase control. We were able to select a range with good performance as the operating point. In addition, the current detection voltage was selected to be approximately 6 V at maximum so that the DC (feedback) amplifier 10 could be used with one power supply operation, and the feedback circuit could be simplified without deteriorating its performance. In addition, the diode D ₃ and capacitor C ₃ included in the gate circuit for constant current control shown in Fig. 3 are shared by the synchronous current circuit for gate signal generation and the current circuit for the feedback circuit to further simplify the circuit. Further, as a current soft start operation, it is possible to provide a circuit including diodes D ₄ , D ₅ , capacitor C ₁ and resistor R ₃ so as to reduce errors in demagnetizing current due to rush current. In addition, the power supply for the DC (feedback) amplifier 10 requires two systems, +15V and -15V, and also UJT11.
The power supply of the excitation signal circuit is to obtain power synchronization by changing the waveform of the full wave rectifier circuit BR to resistor _R4 and Zena diode.
Because the waveform clipped by ZD ₁ is a trapezoidal wave, the power supply for the DC (feedback) amplifier 10 needed to be provided separately in the past, but a full-wave rectifier circuit is used as in the circuit shown in Figure 3. With BR and diode D ₃ capacitor C ₃ and further Zena diode ZD ₂ approx.
With 6V, the purpose can be achieved with one power supply.

In this way, the desired target value ±
+0.67% and -0.5%, which are much higher than 2%, can be obtained, and a compact, lightweight, and inexpensive device can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a permanent magnetic chuck, FIG. 2 is a connection diagram of a control circuit for magnetization/demagnetization according to this invention, and FIG. 3 is a connection diagram of a gate circuit for constant current control in FIG. In the figure, 1 is the iron box of the permanent magnetic chuck, 2 is the suction plate,
3 is a permanent magnet, 4 is a magnetizing/demagnetizing coil, 5 is an internal magnetic pole, 6 is a magnetized object, 7 is a diode bridge circuit, 8 is a triac, 9 is a gate circuit for constant current control, VR is a standard voltage setting device, 10 is a DC (feedback) amplifier, 11 is a UJT, 12p, 12s are the primary and secondary windings of the control transformer, R ₁ is a limiting resistor,
R ₂ is a detection resistor.

Claims (1)

[Scope of utility model registration request] A chuck with a built-in coil for both magnetization and demagnetization is provided with a switch to change the excitation direction of the coil, and especially for demagnetization, a triax is provided on the AC side of the rectifier circuit, while a series current is connected to the excitation coil on the DC side. The AC phase control of the triax is performed using the detection voltage from the detection resistor and the current limiting resistor, and the ratio of these two resistances is appropriately selected so that a range with good linearity is selected as the operating point during AC phase control. A control device for attaching and demagnetizing a permanent magnetic chuck, characterized by: