A contact protection unit and an induction heating device

Abstract

The invention discloses a contact protection unit and an induction heating device, and relates to the technical field of induction heating power supply. The contact protection unit is used for real-time monitoring of the state between a heating sensor and a heated workpiece, and sending a state signal; the contact protection unit comprises a signal sampling circuit, a first-level signal amplification circuit, a second-level signal amplification circuit, a relay drive and signal output circuit, a signal preprocessing circuit, a signal comparison circuit, a signal isolation drive and signal output circuit.

Description

Technical Field

[0001] The invention relates to the technical field of induction heating power supply, in particular to a contact protection unit and an induction heating device. Background Art

[0002] The induction heating devices currently used in the industry do not have a reliable contact protection device between the sensor and the workpiece. The importance of this part of the device has been ignored during the design and manufacturing process of the entire machine, resulting in the surface of the heated workpiece being burned due to other factors when the sensor applies energy to the heated workpiece (the temperature of the heated workpiece exceeds the limit value, causing melting or electric shock). When the sensor contacts the workpiece, the supporting heating power supply and machine tool control system cannot accurately obtain status information, and thus cannot reliably perform shutdown protection. During the process of participating in machine tool control, the CNC system cannot quickly and accurately obtain the contact information between the sensor and the heated workpiece, and thus cannot perform the corresponding positioning action. Summary of the invention

[0003] In view of the defects existing in the prior art, the object of the present invention is to provide a contact protection unit and an induction heating device. The contact protection unit is reasonably and reliably designed, easy to install, has high detection accuracy and fast response speed.

[0004] In order to achieve the above purpose, the technical solution adopted by the present invention is: a contact protection unit, which is used to monitor the state between the heating sensor and the heated workpiece in real time and send a state signal; it includes a signal sampling circuit, a signal first-level amplification circuit, a signal second-level amplification circuit, a relay drive and signal output circuit, a signal preprocessing circuit, a signal comparison circuit, a signal isolation drive and signal output circuit; the signal sampling circuit is connected to an external sampling sensor, and is used to pre-process the output signal of the sampling sensor and transmit it to the subsequent circuit; the signal first-level amplification circuit is connected to the signal sampling circuit, and is used to amplify the output signal of the signal sampling circuit and transmit it to the subsequent circuit; the signal preprocessing circuit is connected to the signal sampling circuit, and is used to compare the signal sampling circuit with the signal sampling circuit. The output signal is pre-processed; the signal secondary amplifier circuit is connected to the signal primary amplifier circuit, and is used to amplify the output signal of the signal primary amplifier circuit again, and transmit it to the peripheral signal connection device; the signal comparison circuit is connected to the signal secondary amplifier circuit, and is used to compare the signal of the previous stage with the set signal, and output it to the subsequent stage circuit after reaching the set value; the relay drive and signal output circuit is connected to the signal comparison circuit, and is used to drive the relay coil, so as to change the normally open point and normally closed point state of the relay, and then transmit the signal to the peripheral signal connection device; the signal isolation drive and signal output circuit is connected to the signal comparison circuit, and is used to isolate the voltage signal, and is connected to the peripheral signal connection device by the output end of the optocoupler.

[0005] A further improvement is that: the signal sampling circuit includes a resistor R23, a resistor R24 ​​and a resistor R25; the output end of the sampling sensor is connected to the input end of the resistor R24 ​​and the input end of the resistor R25 respectively; the two ends of the resistor R23 are connected to the output end of the resistor R24 ​​and the output end of the resistor R25 respectively.

[0006] Further improvements are as follows: the first-level signal amplification circuit includes a resistor R19, a resistor R17, an operational amplifier U1B and a resistor R9; the connection line between the resistor R25 and the resistor R23 is respectively connected to the input end of the resistor R19 and the input end of the resistor R17; the reverse input terminal 6 pin of the operational amplifier U1B is respectively connected to the output end of the resistor R19 and the output end of the resistor R17; the same-direction input terminal 5 pin of the operational amplifier U1B is connected to the common ground through a resistor R11; a selection circuit is connected between the reverse input terminal 6 pin of the operational amplifier U1B and the output terminal 7 pin of the operational amplifier U1B; the output terminal 7 pin of the operational amplifier U1B is connected to the resistor R9.

[0007] A further improvement is that the selection circuit is composed of a dip switch and resistors R1, R2, R3 and R4 connected in parallel.

[0008] Further improvements are as follows: the signal preprocessing circuit includes a diode D4, a diode D3, and an operational amplifier U1A; the positive electrode of the diode D4 is connected to the line between the resistor R23 and the resistor R25; the negative electrode of the diode D4 is connected to the output terminal pin 1 of the operational amplifier U1A; the reverse input terminal pin 2 of the operational amplifier U1A is connected to the line between the resistor R23 and the resistor R24; the same-direction input terminal pin 3 of the operational amplifier U1A is connected to the common ground through the resistor R12; the positive electrode of the diode D3 is connected to the line between the negative electrode of the diode D4 and the output terminal pin 1 of the operational amplifier U1A; the negative electrode of the diode D3 is connected to the reverse input terminal pin 2 of the operational amplifier U1A, and is also connected to the line between the resistor R23 and the resistor R24.

[0009] Further improvements are: the signal secondary amplification circuit includes an operational amplifier U1C, an operational amplifier U1D, and a resistor R7; the input end of the resistor R7 is connected to the output end of the resistor R9, and the output end of the resistor R7 is connected to the common ground through the capacitor C1; the reverse input terminal 9 pin of the operational amplifier U1C is directly connected to the output terminal 8 pin of the operational amplifier U1C; the same-direction input terminal 10 pin of the operational amplifier U1C is connected to the connection between the resistor R7 and the capacitor C1; the output terminal 8 pin of the operational amplifier U1C is connected to the connection between the resistor R7 and the resistor R9 through the capacitor C4; the reverse input terminal 13 pin of the operational amplifier U1D is directly connected to the output terminal 14 pin of the operational amplifier U1D; the same-direction input terminal 12 pin of the operational amplifier U1D is connected to the output terminal 8 pin of the operational amplifier U1C; the output terminal 14 pin of the operational amplifier U1D is connected to the connection terminal CON1 through the resistor R12.

[0010] Further improvements are: the signal comparison circuit includes a comparator U2, a resistor R14 and a resistor R15; the input end of the resistor R15 is connected to the connection between the capacitor C4 and the output terminal 8 pin of the operational amplifier U1C, and the output end of the resistor R15 is connected to the same-direction input terminal 2 pin of the comparator U2; the reverse input terminal 3 pin of the comparator U2 is connected to the power supply V+ through a resistor R16; the same-direction input terminal 2 pin of the comparator U2 is connected to the output terminal 7 pin of the comparator U2 through a resistor R8; the input end of the resistor R14 is connected to the connection between the reverse input terminal 3 pin of the comparator U2 and the resistor R16, and the output end of the resistor R14 is connected to the common ground line.

[0011] Further improvements are: the relay drive and signal output circuit includes a resistor R6, a resistor R10, a transistor T1, and a relay KA1; the input end of the resistor R6 is connected to the output end 7 of the comparator U2, and the output end of the resistor R6 is connected to the base of the transistor T1; one end of the resistor R10 is connected to the connection between the resistor R6 and the base of the transistor T1, and the other end of the resistor R10 is connected to the common ground; the emitter of the transistor T1 is connected to the common ground; the collector of the transistor T1 is connected to the negative pole of the relay KA1 coil; the positive pole of the relay KA1 coil is connected to the power supply V+; the positive and negative poles of the relay KA1 coil are anti-parallel connected with a diode D2; the relay KA1 has a normally open contact CON2, a normally open contact CON4, a normally closed contact CON3, and a contact CON5.

[0012] Further improvements are: the relay drive and signal output circuit includes an optocoupler U3 and a diode D1; pin 3 of the optocoupler U3 is connected to pin 7 of the output terminal of the comparator U2, and pin 2 of the optocoupler U3 is connected to the common ground via a resistor R5; pin 5 of the output terminal of the optocoupler U3 is connected to the wiring terminal CON7; the anode of the diode D1 is connected to pin 8 of the output terminal of the optocoupler U3, and the cathode of the diode D1 is connected to the wiring terminal CON6.

[0013] The present invention also provides an induction heating device, comprising a three-phase input power supply, an isolating switch, a three-phase current detection unit, a fast fuse, a three-phase fully controlled rectifier bridge, a DC smoothing reactor, a thyristor, an inverter bridge, a compensation capacitor, a transformer, a heating sensor, an IGBT transistor induction heating power supply main control unit, and a matching machine tool electronic control system; it also includes a sampling sensor and a contact protection unit as described above; the sampling sensor is connected to one pole of the heating sensor and a heated workpiece; when the sampling sensor detects that the heating sensor is in contact with the heated workpiece, the contact protection unit quickly sends a high / low level signal and an I / O signal to the matching machine tool electronic control system and the IGBT transistor induction heating power supply main control unit, and the corresponding induction heating power supply and machine tool perform corresponding functional actions.

[0014] The beneficial effects of the present invention are:

[0015] In the present invention, the output terminal CON1 of the contact protection unit outputs a level signal after the heating sensor is detected to be in contact with the workpiece, the output terminals CON2 and CON4 form a group of output signals, which are connected after the heating sensor is detected to be in contact with the workpiece, CON3 and CON5 form a group of output signals, which are disconnected after the heating sensor is detected to be in contact with the workpiece, CON6 and CON7 form a group of high-speed output signals, which quickly output high and low level signals after the heating sensor is detected to be in contact with the workpiece, the design is reasonable and reliable, the installation is convenient, the detection accuracy is high, and the response speed is fast. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a circuit diagram of a contact protection unit in an embodiment of the present invention;

[0017] Figure 2 Schematic diagram of a circuit of an induction heating device in an embodiment of the present invention.

[0018] Reference numerals:

[0019] 100-three-phase input power supply; 101-isolating switch; 102-three-phase current detection unit; 103-fast fuse; 104-three-phase fully controlled rectifier bridge; 105-DC smoothing reactor; 106-thyristor; 107-inverter bridge; 108-compensation capacitor; 109-transformer; 110-heating sensor; 111-sampling sensor; 112-IGBT transistor induction heating power supply main control unit; 113-matching machine tool electronic control system; 200-contact protection unit; 201-signal sampling circuit; 202-signal first-stage amplification circuit; 203-signal second-stage amplification circuit; 204-relay drive and signal output circuit; 205-signal preprocessing circuit; 206-signal comparison circuit; 207-signal isolation drive and signal output circuit. DETAILED DESCRIPTION

[0020] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions.

[0021] The following is a further description of the specific embodiments of the present invention in conjunction with the drawings of the specification, so that the technical solution and its beneficial effects of the present invention are clearer and more explicit. The following description of the embodiments with reference to the drawings is exemplary and intended to explain the present invention, but cannot be understood as limiting the present invention.

[0022] See also Figure 1 As shown, an embodiment of the present invention provides a contact protection unit for real-time monitoring of the state between a heating sensor and a heated workpiece and sending a state signal; comprising a signal sampling circuit 201, a first-level signal amplification circuit 202, a second-level signal amplification circuit 203, a relay drive and signal output circuit 204, a signal preprocessing circuit 205, a signal comparison circuit 206, and a signal isolation drive and signal output circuit 207;

[0023] The signal sampling circuit 201 is connected to the external sampling sensor 111 and is used to pre-process the output signal of the sampling sensor 111 and transmit it to the subsequent circuit; the sampling sensor 111 can be a Hall sensor or a current sensor.

[0024] The first-stage signal amplifying circuit 202 is connected to the signal sampling circuit 201, and is used to amplify the output signal of the signal sampling circuit 201 and transmit it to the subsequent circuit;

[0025] The signal preprocessing circuit 205 is connected to the signal sampling circuit 201 and is used to preprocess the output signal of the signal sampling circuit 201;

[0026] The signal secondary amplifier circuit 203 is connected to the signal primary amplifier circuit 202, and is used to amplify the output signal of the signal primary amplifier circuit 202 again, and transmit it to the peripheral signal connection device;

[0027] The signal comparison circuit 206 is connected to the signal secondary amplification circuit 203, and is used to compare the signal of the previous stage with the set signal, and output it to the subsequent stage circuit after reaching the set value;

[0028] The relay driving and signal output circuit 204 is connected to the signal comparison circuit 206 and is used to drive the relay coil, thereby changing the normally open point and normally closed point states of the relay, and then transmitting the signal to the peripheral signal connection device;

[0029] The signal isolation driving and signal output circuit 207 is connected to the signal comparison circuit 206 and is used to isolate the voltage signal and connect the output end of the optical coupler to the peripheral signal connection device.

[0030] Specifically, the signal sampling circuit 201 includes resistors R23, R24 and R25; the output end of the sampling sensor 111 is connected to the input end of the resistor R24 ​​and the input end of the resistor R25 respectively; the two ends of the resistor R23 are connected to the output end of the resistor R24 ​​and the output end of the resistor R25 respectively.

[0031] Specifically, the first-level signal amplification circuit 202 includes a resistor R19, a resistor R17, an operational amplifier U1B and a resistor R9; the connection between the resistor R25 and the resistor R23 is respectively connected to the input end of the resistor R19 and the input end of the resistor R17; the reverse input terminal 6 pin of the operational amplifier U1B is respectively connected to the output end of the resistor R19 and the output end of the resistor R17; the same-direction input terminal 5 pin of the operational amplifier U1B is connected to the common ground through the resistor R11; a selection circuit is connected between the reverse input terminal 6 pin of the operational amplifier U1B and the output terminal 7 pin of the operational amplifier U1B; the output terminal 7 pin of the operational amplifier U1B is connected to the resistor R9.

[0032] Specifically, the selection circuit is composed of a dip switch and a resistor R1 , a resistor R2 , a resistor R3 , and a resistor R4 connected in parallel.

[0033] Specifically, the signal preprocessing circuit 205 includes a diode D4, a diode D3, and an operational amplifier U1A; the anode of the diode D4 is connected to the line between the resistor R23 and the resistor R25; the cathode of the diode D4 is connected to the output pin 1 of the operational amplifier U1A; the reverse input pin 2 of the operational amplifier U1A is connected to the line between the resistor R23 and the resistor R24; the non-inverting input pin 3 of the operational amplifier U1A is connected to the common ground through the resistor R12; the anode of the diode D3 is connected to the line between the cathode of the diode D4 and the output pin 1 of the operational amplifier U1A; the cathode of the diode D3 is connected to the reverse input pin 2 of the operational amplifier U1A, and is also connected to the line between the resistor R23 and the resistor R24.

[0034] Specifically, the signal secondary amplification circuit 203 includes an operational amplifier U1C, an operational amplifier U1D, and a resistor R7; the input end of the resistor R7 is connected to the output end of the resistor R9, and the output end of the resistor R7 is connected to the common ground through the capacitor C1; the reverse input terminal 9 pin of the operational amplifier U1C is directly connected to the output terminal 8 pin of the operational amplifier U1C; the same-direction input terminal 10 pin of the operational amplifier U1C is connected to the connection between the resistor R7 and the capacitor C1; the output terminal 8 pin of the operational amplifier U1C is connected to the connection between the resistor R7 and the resistor R9 through the capacitor C4; the reverse input terminal 13 pin of the operational amplifier U1D is directly connected to the output terminal 14 pin of the operational amplifier U1D; the same-direction input terminal 12 pin of the operational amplifier U1D is connected to the output terminal 8 pin of the operational amplifier U1C; the output terminal 14 pin of the operational amplifier U1D is connected to the connection terminal CON1 through the resistor R12.

[0035] Specifically, the signal comparison circuit 206 includes a comparator U2, a resistor R14 and a resistor R15; the input end of the resistor R15 is connected to the connection between the capacitor C4 and the output terminal 8 pin of the operational amplifier U1C, and the output end of the resistor R15 is connected to the same-direction input terminal 2 pin of the comparator U2; the reverse input terminal 3 pin of the comparator U2 is connected to the power supply V+ through the resistor R16; the same-direction input terminal 2 pin of the comparator U2 is connected to the output terminal 7 pin of the comparator U2 through the resistor R8; the input end of the resistor R14 is connected to the connection between the reverse input terminal 3 pin of the comparator U2 and the resistor R16, and the output end of the resistor R14 is connected to the common ground line.

[0036] Specifically, the relay drive and signal output circuit 204 includes a resistor R6, a resistor R10, a transistor T1, and a relay KA1; the input end of the resistor R6 is connected to the output terminal 7 of the comparator U2, and the output end of the resistor R6 is connected to the base of the transistor T1; one end of the resistor R10 is connected to the connection between the resistor R6 and the base of the transistor T1, and the other end of the resistor R10 is connected to the common ground; the emitter of the transistor T1 is connected to the common ground; the collector of the transistor T1 is connected to the negative pole of the relay KA1 coil; the positive pole of the relay KA1 coil is connected to the power supply V+; the positive and negative poles of the relay KA1 coil are anti-parallel connected with a diode D2; the relay KA1 has a normally open contact CON2, a normally open contact CON4, a normally closed contact CON3, and a contact CON5.

[0037] Specifically, the relay drive and signal output circuit 204 includes an optocoupler U3 and a diode D1; pin 3 of the optocoupler U3 is connected to pin 7 of the output terminal of the comparator U2, and pin 2 of the optocoupler U3 is connected to the common ground via a resistor R5; pin 5 of the output terminal of the optocoupler U3 is connected to the wiring terminal CON7; the anode of the diode D1 is connected to pin 8 of the output terminal of the optocoupler U3, and the cathode of the diode D1 is connected to the wiring terminal CON6.

[0038] See also Figure 2 As shown, the embodiment of the present invention also provides an induction heating device, including a three-phase input power supply 100 for providing power input, an isolating switch 101 for protecting power supply overload and safety shunt, a three-phase current detection unit (three-phase current detection transformer) 102 installed on the incoming line, fast fuses 103 respectively connected in series to the three-phase input power supply, a three-phase fully controlled rectifier bridge 104 for rectifying the three-phase power frequency power into pulsating direct current, a direct current smoothing reactor 105 for filtering the single-phase pulsating direct current into a relatively smooth direct current, a thyristor 106 connected to the output end of the smoothing reactor and turned on for protection in extreme cases, and an inverter bridge 107 for converting direct current into single-phase alternating current of a required frequency, and connected to the output end of the inverter bridge The invention also comprises an LC resonant circuit compensation capacitor 108, a transformer 109 for adjusting the power supply output frequency value, voltage and current ratio, a heating sensor 110 connected to the secondary output end of the transformer, an IGBT transistor induction heating power supply main control unit 112 for power supply operation control, and a matching machine tool electronic control system 113; it also includes a sampling sensor 111 and a contact protection unit 200 as described above; the sampling sensor 111 is connected to one pole of the heating sensor 110 and the heated workpiece; when the sampling sensor 111 detects that the heating sensor 110 is in contact with the heated workpiece, the contact protection unit 200 quickly sends a high / low level signal and an I / O signal to the matching machine tool electronic control system 113 and the IGBT (Insulated Gate Bipolar Transistor) transistor induction heating power supply main control unit 112, and the corresponding induction heating power supply and machine tool perform corresponding functional actions.

[0039] The main incoming power circuit breaker is used to control the connection and disconnection of the incoming power; the current transformer is used to detect the working current value of the power supply; the fast fuse is used to protect the three-phase fully controlled rectifier bridge; the three-phase fully controlled rectifier bridge is used to rectify the three-phase AC power into pulsating DC power; the smoothing reactor is used to smooth the pulsating DC power into single-phase smooth DC power; the inverter bridge module is used to invert the single-phase smooth DC power into the AC power required by the induction heated object; the isolation transformer is used to match the power supply output voltage and current ratio and frequency value, the resonant capacitor is used to charge and discharge the inverter workload, the heating sensor is used to convert the inverter's AC power into magnetic energy and apply it to the heated metal object, and the contact protection unit is used to monitor the status between the heating sensor and the heated workpiece in real time, and send the status signal to the machine tool control system and the inductor heating power supply main control system in real time. In this embodiment, the matching machine tool electronic control system is a standard product on the market. Currently, this device can correspond to Siemens industrial control products (808D CNC, 828D CNC, 840D CNC, 840DSL CNC, S7 series PLC products), Japan Mitsubishi industrial control products (FX series PLC products, Mitsubishi CNC products), and Japan Omron industrial control products (Omron PLC products).

[0040] The working principle of the present invention is:

[0041] When the heating sensor comes into contact with the heated workpiece, CON1 of the contact protection unit immediately sends a high-level signal, which is transmitted to the corresponding matching machine tool control system through the lead wire. The control system executes the corresponding action or outputs the instruction according to the internal control requirements.

[0042] When the heating sensor comes into contact with the heated workpiece, CON2-CON4 of the contact protection unit is immediately connected and transmitted to the corresponding supporting machine tool control system through the lead wire. The control system executes the corresponding action or outputs the instruction according to the internal control requirements (stops the servo axis movement, issues an alarm prompt, memorizes the current coordinates, executes the corresponding protection instruction, transmits the signal through the communication instruction or cable, sends a stop signal to the IGBT transistor induction heating power supply main control unit or triggers an alarm prompt).

[0043] When the heating sensor comes into contact with the heated workpiece, CON3-CON5 of the contact protection unit is immediately disconnected and transmitted to the corresponding supporting machine tool control system through the lead wire. The control system executes the corresponding action or outputs the instruction according to the internal control requirements (stops the servo axis movement, issues an alarm prompt, memorizes the current coordinates, executes the corresponding protection instruction, transmits the signal through the communication instruction or cable, sends a stop signal to the IGBT transistor induction heating power supply main control unit or triggers an alarm prompt).

[0044] When the heating sensor comes into contact with the heated workpiece, CON6-CON7 of the contact protection unit is immediately connected and transmitted to the corresponding matching machine tool control system through the lead wire, converting the pre-set high-level signal into a low-level signal. The control system executes the corresponding action or outputs the instruction (stops the servo axis movement, issues an alarm, memorizes the current coordinates, and executes the corresponding protection instruction) according to the internal control requirements.

[0045] In the description of the specification, the description with reference to the terms "one embodiment", "preferably", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention, and the schematic expressions of the above terms in this specification do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0046] The present invention is not limited to the above-mentioned embodiments. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention. The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A contact protection unit for real-time monitoring of the state between a heating sensor and a heated workpiece and sending a state signal; characterized in that: It comprises a signal sampling circuit (201), a first-level signal amplification circuit (202), a second-level signal amplification circuit (203), a relay drive and signal output circuit (204), a signal preprocessing circuit (205), a signal comparison circuit (206), and a signal isolation drive and signal output circuit (207); The signal sampling circuit (201) is connected to an external sampling sensor (111) and is used to pre-process the output signal of the sampling sensor (111) and transmit it to a subsequent circuit; The first-stage signal amplification circuit (202) is connected to the signal sampling circuit (201) and is used to amplify the output signal of the signal sampling circuit (201) and transmit it to a subsequent circuit; The signal preprocessing circuit (205) is connected to the signal sampling circuit (201) and is used to preprocess the output signal of the signal sampling circuit (201); The secondary signal amplifying circuit (203) is connected to the primary signal amplifying circuit (202) and is used to amplify the output signal of the primary signal amplifying circuit (202) again and transmit it to a peripheral signal connecting device; The signal comparison circuit (206) is connected to the signal secondary amplification circuit (203) and is used to compare the signal of the previous stage with the set signal and output it to the subsequent stage circuit after reaching the set value; The relay driving and signal output circuit (204) is connected to the signal comparison circuit (206) and is used to drive the relay coil, thereby changing the normally open point and normally closed point states of the relay, and then transmitting the signal to the peripheral signal connection device; The signal isolation drive and signal output circuit (207) is connected to the signal comparison circuit (206) and is used to isolate the voltage signal and connect the output end of the optical coupler to a peripheral signal connection device; The signal sampling circuit (201) comprises a resistor R23, a resistor R24 ​​and a resistor R25; the output end of the sampling sensor (111) is respectively connected to the input end of the resistor R24 ​​and the input end of the resistor R25; the two ends of the resistor R23 are respectively connected to the output end of the resistor R24 ​​and the output end of the resistor R25; The signal primary amplification circuit (202) comprises a resistor R19, a resistor R17, an operational amplifier U1B and a resistor R9; the connection line between the resistor R25 and the resistor R23 is respectively connected to the input end of the resistor R19 and the input end of the resistor R17; the reverse input end pin 6 of the operational amplifier U1B is respectively connected to the output end of the resistor R19 and the output end of the resistor R17; the same-direction input end pin 5 of the operational amplifier U1B is connected to a common ground line through a resistor R11; a selection circuit is connected between the reverse input end pin 6 of the operational amplifier U1B and the output end pin 7 of the operational amplifier U1B; the output end pin 7 of the operational amplifier U1B is connected to the resistor R9; The signal preprocessing circuit (205) comprises a diode D4, a diode D3, and an operational amplifier U1A; the anode of the diode D4 is connected to the line between the resistor R23 and the resistor R25; the cathode of the diode D4 is connected to the output terminal pin 1 of the operational amplifier U1A; the reverse input terminal pin 2 of the operational amplifier U1A is connected to the line between the resistor R23 and the resistor R24; the non-inverting input terminal pin 3 of the operational amplifier U1A is connected to the common ground line through the resistor R12; the anode of the diode D3 is connected to the line between the cathode of the diode D4 and the output terminal pin 1 of the operational amplifier U1A; the cathode of the diode D3 is connected to the reverse input terminal pin 2 of the operational amplifier U1A, and is also connected to the line between the resistor R23 and the resistor R24.

2. The contact protection unit according to claim 1, characterized in that: The selection circuit is composed of a dip switch and a resistor R1, a resistor R2, a resistor R3, and a resistor R4 connected in parallel.

3. The contact protection unit according to claim 1, characterized in that: The signal secondary amplification circuit (203) comprises an operational amplifier U1C, an operational amplifier U1D, and a resistor R7; the input end of the resistor R7 is connected to the output end of the resistor R9, and the output end of the resistor R7 is connected to the common ground line via a capacitor C1; the reverse input end pin 9 of the operational amplifier U1C is directly connected to the output end pin 8 of the operational amplifier U1C; the same-direction input end pin 10 of the operational amplifier U1C is connected to the connection between the resistor R7 and the capacitor C1; the output end pin 8 of the operational amplifier U1C is connected to the connection between the resistor R7 and the resistor R9 via a capacitor C4; the reverse input end pin 13 of the operational amplifier U1D is directly connected to the output end pin 14 of the operational amplifier U1D; the same-direction input end pin 12 of the operational amplifier U1D is connected to the output end pin 8 of the operational amplifier U1C; the output end pin 14 of the operational amplifier U1D is connected to the connection terminal CON1 via a resistor R12.

4. The contact protection unit according to claim 3, characterized in that: The signal comparison circuit (206) comprises a comparator U2, a resistor R14 and a resistor R15; the input end of the resistor R15 is connected to the connection between the capacitor C4 and the output end 8 pin of the operational amplifier U1C, and the output end of the resistor R15 is connected to the same direction input end 2 pin of the comparator U2; the reverse input end 3 pin of the comparator U2 is connected to the power supply V+ through the resistor R16; the same direction input end 2 pin of the comparator U2 is connected to the output end 7 pin of the comparator U2 through the resistor R8; the input end of the resistor R14 is connected to the connection between the reverse input end 3 pin of the comparator U2 and the resistor R16, and the output end of the resistor R14 is connected to the common ground line.

5. The contact protection unit according to claim 4, characterized in that: The relay drive and signal output circuit (204) comprises a resistor R6, a resistor R10, a transistor T1, and a relay KA1; the input end of the resistor R6 is connected to the output end 7 of the comparator U2, and the output end of the resistor R6 is connected to the base of the transistor T1; one end of the resistor R10 is connected to the connection between the resistor R6 and the base of the transistor T1, and the other end of the resistor R10 is connected to the common ground; the emitter of the transistor T1 is connected to the common ground; the collector of the transistor T1 is connected to the negative pole of the relay KA1 coil; the positive pole of the relay KA1 coil is connected to the power supply V+; the positive and negative poles of the relay KA1 coil are anti-parallel connected with a diode D2; the relay KA1 has a normally open contact CON2, a normally open contact CON4, a normally closed contact CON3, and a contact CON5.

6. The contact protection unit according to claim 4, characterized in that: The relay drive and signal output circuit (204) comprises an optocoupler U3 and a diode D1; pin 3 of the optocoupler U3 is connected to pin 7 of the output terminal of the comparator U2, and pin 2 of the optocoupler U3 is connected to the common ground via a resistor R5; pin 5 of the output terminal of the optocoupler U3 is connected to a wiring terminal CON7; the anode of the diode D1 is connected to pin 8 of the output terminal of the optocoupler U3, and the cathode of the diode D1 is connected to a wiring terminal CON6.

7. An induction heating device, comprising a three-phase input power supply (100), an isolating switch (101), a three-phase current detection unit (102), a fast fuse (103), a three-phase fully controlled rectifier bridge (104), a DC smoothing reactor (105), a thyristor (106), an inverter bridge (107), a compensation capacitor (108), a transformer (109), a heating sensor (110), an IGBT transistor induction heating power supply main control unit (112), and a matching machine tool electronic control system (113); characterized in that: It also includes a sampling sensor (111) and a contact protection unit (200) as claimed in claim 1; the sampling sensor (111) is connected to one pole of the heating sensor (110) and the heated workpiece; when the sampling sensor (111) detects that the heating sensor (110) is in contact with the heated workpiece, the contact protection unit (200) quickly sends a high / low level signal and an I / O signal to the matching machine tool electronic control system (113) and the IGBT transistor induction heating power supply main control unit (112), and the corresponding induction heating power supply and machine tool perform corresponding functional actions.

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