Safety protection circuit of gantry crane
By designing safety protection circuits for the power supply module, motor control module, overload detection module, and protection control module, the safety hazards of gantry cranes caused by thermal relay failures were solved, effective overload power-off protection was achieved, and the safety of gantry cranes was improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- 山东冠华重工机械有限公司
- Filing Date
- 2025-04-11
- Publication Date
- 2026-05-19
AI Technical Summary
In the existing safety protection circuit of gantry cranes, the thermal relay cannot properly cut off the power protection when it fails, resulting in a safety hazard.
A safety protection circuit is designed, comprising a power supply module, a motor control module, an overload detection module, an alarm detection module, and a protection control module. The motor control module receives and processes the electrical energy, the overload detection module performs current sampling and rectification filtering, the alarm detection module displays the overload without power interruption, and the protection control module assists in power cut-off to improve safety.
It achieves effective power-off protection under overload conditions and in case of thermal relay failure, thus improving the safety of the gantry crane.
Smart Images
Figure CN224264688U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of gantry crane protection technology, specifically a safety protection circuit for gantry cranes. Background Technology
[0002] Gantry cranes, also known as portal cranes, are a type of bridge crane. To protect against overload, existing gantry cranes typically use a safety protection circuit composed of thermal relays. In the event of an overload, the circuit cuts off power and stops the gantry crane from operation. However, when the thermal relays malfunction, the gantry crane will fail to cut off power properly during an overload, posing a safety hazard. Therefore, improvements are needed. Utility Model Content
[0003] This utility model provides a safety protection circuit for a gantry crane to solve the problems mentioned in the background art.
[0004] To achieve the above objectives, this utility model provides the following technical solution:
[0005] A safety protection circuit for a gantry crane includes: a power supply module, a motor control module, a motor module, an overload detection module, an alarm detection module, and a protection control module;
[0006] The power module is used to receive three-phase power, perform short-circuit power failure protection, step down the three-phase power and output the first power.
[0007] The motor control module, connected to the power supply module and the motor module, is used to receive the first electrical energy and provide overload power-off protection for the motor module, perform self-locking start control for the motor module, and transmit three-phase electrical energy to the motor module.
[0008] The motor module is used to receive three-phase electrical energy transmitted from the motor control module and control the gantry crane motor to start;
[0009] The overload detection module, connected to the motor module, is used to sample and rectify the three-phase power input to the motor control module, and output a second detection signal when the voltage of the processed signal is greater than the set overload threshold.
[0010] The alarm detection module is connected to the power supply module and the motor control module. It is used to receive the first electrical energy and output the first detection signal when the motor control module is overloaded and the power is not cut off. When the motor control module performs overload power-off protection, it displays the overload.
[0011] The protection control module, connected to the alarm detection module and the overload detection module, is used to display overload abnormalities and control the motor control module to stop receiving three-phase power when it receives the first detection signal and the second detection signal.
[0012] As a further embodiment of this utility model: the power supply module includes a three-phase power interface, an air switch, a first fuse, a second fuse, a third fuse, and a first transformer; the motor control module includes a first contact switch and a first thermal relay; the motor module includes a first motor; and the overload detection module includes a first current transformer.
[0013] Preferably, the first, second, and third terminals of the three-phase power interface are connected to the first stationary terminal, second stationary terminal, and third stationary terminal of the air switch, respectively. The first moving terminal of the air switch is connected to the first terminal of the primary side of the first transformer and the first stationary terminal of the first contact switch via a first fuse. The second moving terminal of the air switch is connected to the second stationary terminal of the first contact switch via a second fuse. The third moving terminal of the air switch is connected to the second terminal of the primary side of the first transformer and the third stationary terminal of the first contact switch via a third fuse. The first, second, and third moving terminals of the first contact switch are connected to the first, second, and third terminals of the first thermal relay, respectively. The fourth and fifth terminals of the first thermal relay are connected to the first and second terminals of the first motor, respectively. The sixth terminal of the first thermal relay is connected to the first terminal of the first current transformer. The second terminal of the first current transformer is connected to the third terminal of the first motor. The first and second terminals of the secondary side of the first transformer are connected to the alarm detection module.
[0014] As a further embodiment of this utility model: the motor control module further includes a first thermal relay switch, a first push-button switch, a second contact switch, a second push-button switch, and a first contactor; the protection control module includes a first relay switch;
[0015] Preferably, the first stationary terminal and the second stationary terminal of the first thermal relay switch are both connected to the first end of the secondary side of the first transformer. The first moving terminal of the first thermal relay switch is connected to the stationary terminal of the first push-button switch. The moving terminal of the first push-button switch is connected to the stationary terminal of the first relay switch. The moving terminal of the first relay switch is connected to the stationary terminal of the second contact switch and the stationary terminal of the second push-button switch. The moving terminal of the second push-button switch is connected to the stationary terminal of the second contact switch and one end of the first contactor. The other end of the first contactor is connected to the second end of the secondary side of the first transformer. The second moving terminal of the first thermal relay switch is connected to the alarm detection module.
[0016] As a further embodiment of this utility model: the alarm detection module includes a first resistor, a first diode, a first lighting lamp, and a first optocoupler;
[0017] Preferably, the anode of the first diode is connected to the first end of the secondary side of the first transformer through the first resistor, the first end of the first optocoupler is connected to one end of the first lighting lamp, the other end of the first lighting lamp is connected to the second active end of the first thermal relay switch, the second end of the first optocoupler is connected to the second end of the secondary side of the first transformer, the cathode of the first diode is connected to the third end of the first optocoupler and the protection control module, and the fourth end of the first optocoupler is grounded.
[0018] As a further embodiment of this utility model, the overload detection module also includes a first capacitor, a second capacitor, a second resistor, a first rectifier, a third resistor, a third capacitor, a fourth resistor, a fifth resistor, a first power supply, and a first comparator.
[0019] Preferably, one end of the first capacitor is connected to the third end of the first current transformer and the first end of the first rectifier, and is sequentially connected to the other end of the first capacitor, the second end of the first rectifier, and the fourth end of the first current transformer through the second capacitor and the second resistor. The third end of the first rectifier is connected to one end of the third capacitor and the non-inverting input of the first comparator through the third resistor. The fourth end of the first rectifier is connected to the other end of the third capacitor, one end of the fifth resistor, and ground. The other end of the fifth resistor is connected to the inverting input of the first comparator and is connected to the first power supply through the fourth resistor. The output of the first comparator is connected to the protection control module.
[0020] As a further embodiment of this utility model, the protection control module also includes a first logic chip, a first relay, a first switching transistor, a second switching transistor, a first indicator light, a sixth resistor, and a second power supply.
[0021] Preferably, the A and B terminals of the first logic chip are connected to the cathode of the first diode and the output terminal of the first comparator, respectively; the Y terminal of the first logic chip is connected to the base of the first switching transistor and the base of the second switching transistor; the collector of the first switching transistor is connected to one end of the first relay; the other end of the first relay is connected to the second power supply and connected to the anode of the first indicator light through the sixth resistor; the cathode of the first indicator light is connected to the collector of the second switching transistor; and the emitters of both the first and second switching transistors are grounded.
[0022] Compared with the prior art, the beneficial effects of this utility model are as follows: The safety protection circuit of the gantry crane of this utility model can receive the electrical energy output by the power supply module after processing through the motor control module, and control the starting and overload power-off protection of the gantry crane motor in the motor module. The alarm detection module displays the overload power-off, and the overload detection module detects the overload of the electrical energy input to the gantry crane motor. When an overload occurs and the motor control module does not perform overload power-off protection, the protection control module will assist in controlling the power-off operation of the motor control module and display the overload power-off, thereby improving the safety of the gantry crane. Attached Figure Description
[0023] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments of this utility model will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0024] Figure 1 This is a schematic block diagram of the safety protection circuit for a gantry crane, provided as an example of this utility model.
[0025] Figure 2 A circuit diagram of a safety protection circuit for a gantry crane provided for this utility model embodiment.
[0026] Figure 3 A connection circuit diagram of the protection control module provided for this utility model embodiment. Detailed Implementation
[0027] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.
[0028] In one embodiment, see Figure 1 A safety protection circuit for a gantry crane includes: a power supply module 1, a motor control module 2, a motor module 3, an overload detection module 4, an alarm detection module 5, and a protection control module 6.
[0029] Specifically, power module 1 is used to connect to three-phase power, perform short-circuit power failure protection, step down the three-phase power and output the first power.
[0030] The motor control module 2 is connected to the power supply module 1 and the motor module 3. It is used to receive the first electrical energy and provide overload power-off protection for the motor module 3, perform self-locking start control for the motor module 3, and transmit three-phase electrical energy to the motor module 3.
[0031] Motor module 3 is used to receive three-phase electrical energy transmitted from motor control module 2 and control the gantry crane motor to start;
[0032] The overload detection module 4 is connected to the motor module 3 and is used to sample and rectify the three-phase power input to the motor control module 2. When the voltage of the processed signal is greater than the set overload threshold, it outputs a second detection signal.
[0033] The alarm detection module 5 is connected to the power supply module 1 and the motor control module 2. It is used to receive the first electrical energy and output the first detection signal when the motor control module 2 is overloaded and not powered off. When the motor control module 2 performs overload power-off protection, it displays the overload.
[0034] The protection control module 6 is connected to the alarm detection module 5 and the overload detection module 4. It is used to display the overload abnormality and control the motor control module 2 to stop receiving three-phase power when it receives the first detection signal and the second detection signal.
[0035] In a specific embodiment, the power supply module 1 can be a power circuit composed of a three-phase power interface, an air switch QS, and fuses, which can receive three-phase power and perform short-circuit power-off control and voltage reduction regulation on the three phases; the motor control module 2 can be a motor control circuit composed of thermal relays, contactors, and push-button switches, which controls the self-locking start, power-off, and overload power-off protection of the motor module 3; the motor module 3 can be a motor circuit composed of a gantry crane motor, which receives the power transmitted from the motor control module 2 and rotates it; the overload detection module 4 can be an overload detection circuit composed of current transformers, resistors, rectifiers, and comparators, which can sample the current of the power input to the motor module 3. The signal is rectified and filtered, and the processed signal is compared with the voltage magnitude of the set overload threshold to determine whether the motor module 3 is overloaded. The alarm detection module 5 can be an alarm detection circuit composed of lighting lamps, resistors, optocouplers, etc., which can display the overload power-off when overloaded and detect the overload protection status of the motor control module 2. The protection control module 6 can be a protection control circuit composed of logic chips, transistors, relays, etc., which can determine whether the motor control module 2 performs overload power-off protection when overloaded based on the signals output by the overload detection module 4 and the alarm detection module 5, and control the motor control module 2 to cut off power and display the overload power-off when the overload power-off is abnormal.
[0036] In another embodiment, please refer to Figure 1 , Figure 2 and Figure 3 The power module 1 includes a three-phase power interface, an air switch QS, a first fuse FU1, a second fuse FU2, a third fuse FU3, and a first transformer B1; the motor control module 2 includes a first contact switch KM-1 and a first thermal relay FR; the motor module 3 includes a first motor M1; and the overload detection module 4 includes a first current transformer PT1.
[0037] Specifically, the first, second, and third terminals of the three-phase power interface are connected to the first stationary terminal, second stationary terminal, and third stationary terminal of the air switch QS, respectively. The first moving terminal of the air switch QS is connected to the first terminal of the primary side of the first transformer B1 and the first stationary terminal of the first contact switch KM-1 through the first fuse FU1. The second moving terminal of the air switch QS is connected to the second stationary terminal of the first contact switch KM-1 through the second fuse FU2. The third moving terminal of the air switch QS is connected to the second terminal of the primary side of the first transformer B1 and the third stationary terminal of the first contact switch KM-1 through the third fuse FU3. The first, second, and third moving terminals of the first contact switch KM-1 are connected to the first, second, and third terminals of the first thermal relay FR, respectively. The fourth and fifth terminals of the first thermal relay FR are connected to the first and second terminals of the first motor M1, respectively. The sixth terminal of the first thermal relay FR is connected to the first terminal of the first current transformer PT1. The second terminal of the first current transformer PT1 is connected to the third terminal of the first motor M1. The first and second terminals of the secondary side of the first transformer B1 are connected to the alarm detection module 5.
[0038] In a specific embodiment, the first contact switch KM-1 can be a three-pole single-throw switch and is a normally open switch; the first motor M1 is a three-phase motor used in gantry cranes; and the first current transformer PT1 can be a current transformer.
[0039] Furthermore, the motor control module 2 also includes a first thermal relay switch FR-1, a first push-button switch SB1, a second contact switch KM-2, a second push-button switch SB2, and a first contactor KM; the protection control module 6 includes a first relay switch K1-1;
[0040] Specifically, the first stationary terminal and the second stationary terminal of the first thermal relay switch FR-1 are both connected to the first end of the secondary side of the first transformer B1. The first moving terminal of the first thermal relay switch FR-1 is connected to the stationary terminal of the first push-button switch SB1. The moving terminal of the first push-button switch SB1 is connected to the stationary terminal of the first relay switch K1-1. The moving terminal of the first relay switch K1-1 is connected to the stationary terminal of the second contact switch KM-2 and the stationary terminal of the second push-button switch SB2. The moving terminal of the second push-button switch SB2 is connected to the stationary terminal of the second contact switch KM-2 and one end of the first contactor KM. The other end of the first contactor KM is connected to the second end of the secondary side of the first transformer B1. The second moving terminal of the first thermal relay switch FR-1 is connected to the alarm detection module 5.
[0041] In a specific embodiment, the first thermal relay switch FR-1 can be a double-pole single-throw switch, and the first stationary end and the first moving end of the first thermal relay switch FR-1 are normally closed switches, which are controlled by the first thermal relay FR. That is, in the event of overload, the first thermal relay FR controls the first thermal relay switch FR-1 to work; the first relay switch K1-1 can be a normally closed switch; the second contact switch KM-2 can be a normally open switch; the first contactor KM controls the operation of the first contact card switch and the second contact switch KM-2 by magnetic attraction.
[0042] Furthermore, the alarm detection module 5 includes a first resistor R1, a first diode D1, a first lighting lamp HL1, and a first optocoupler U1;
[0043] Specifically, the anode of the first diode D1 is connected to the first terminal of the secondary side of the first transformer B1 through the first resistor R1, the first terminal of the first optocoupler U1 is connected to one terminal of the first lighting lamp HL1, the other terminal of the first lighting lamp HL1 is connected to the second active terminal of the first thermal relay switch FR-1, the second terminal of the first optocoupler U1 is connected to the second terminal of the secondary side of the first transformer B1, the cathode of the first diode D1 is connected to the third terminal of the first optocoupler U1 and the protection control module 6, and the fourth terminal of the first optocoupler U1 is grounded.
[0044] In a specific embodiment, the second moving end and the second stationary end of the first thermal relay switch FR-1 are normally open switches; the first optocoupler U1 can be a TLP510 optocoupler.
[0045] Furthermore, the overload detection module 4 also includes a first capacitor C1, a second capacitor C2, a second resistor R2, a first rectifier T1, a third resistor R3, a third capacitor C3, a fourth resistor R4, a fifth resistor R5, a first power supply VCC1, and a first comparator A1.
[0046] Specifically, one end of the first capacitor C1 is connected to the third end of the first current transformer PT1 and the first end of the first rectifier T1, and is connected in sequence to the other end of the first capacitor C1, the second end of the first rectifier T1 and the fourth end of the first current transformer PT1 through the second capacitor C2 and the second resistor R2. The third end of the first rectifier T1 is connected to one end of the third capacitor C3 and the non-inverting input of the first comparator A1 through the third resistor R3. The fourth end of the first rectifier T1 is connected to the other end of the third capacitor C3, one end of the fifth resistor R5 and the ground terminal. The other end of the fifth resistor R5 is connected to the inverting input of the first comparator A1 and is connected to the first power supply VCC1 through the fourth resistor R4. The output terminal of the first comparator A1 is connected to the protection control module 6.
[0047] In a specific embodiment, the first capacitor C1, the second capacitor C2, and the second resistor R2 are filtered; the first rectifier T1, the third resistor R3, and the third capacitor C3 are rectified and filtered; the first power supply VCC1, the fourth resistor R4, and the fifth resistor R5 are set with overload thresholds; and the first comparator A1 can be an LM358 comparator.
[0048] Furthermore, the protection control module 6 also includes a first logic chip J1, a first relay K1, a first switching transistor V1, a second switching transistor V2, a first indicator LED1, a sixth resistor R6, and a second power supply VCC2;
[0049] Specifically, the A and B terminals of the first logic chip J1 are connected to the cathode of the first diode D1 and the output terminal of the first comparator A1, respectively. The Y terminal of the first logic chip J1 is connected to the base of the first switching transistor V1 and the base of the second switching transistor V2. The collector of the first switching transistor V1 is connected to one end of the first relay K1. The other end of the first relay K1 is connected to the second power supply VCC2 and connected to the anode of the first indicator LED1 through the sixth resistor R6. The cathode of the first indicator LED1 is connected to the collector of the second switching transistor V2. The emitters of the first switching transistor V1 and the second switching transistor V2 are both grounded.
[0050] In a specific embodiment, the first logic chip J1 can be an AND gate chip; the first relay K1 controls the operation of the first relay switch K1-1 by magnetic attraction; the first switch V1 and the second switch V2 can both be NPN transistors; and the first indicator LED1 can be an LED.
[0051] In this embodiment, a safety protection circuit for a gantry crane includes a three-phase power interface that receives three-phase electrical energy. An air switch QS, a first fuse FU1, a second fuse FU2, and a third fuse FU3 handle power transmission and short-circuit protection control. The transmitted energy is stepped down by a first transformer B1 to output the first electrical energy. When the second push-button switch SB2 is pressed, the first contactor KM is energized, and both the first contact switch KM-1 and the second contact switch KM-2 close, controlling the first contactor KM to self-lock. The three-phase electrical energy is then transmitted through the first contact switch KM-1 to the first thermal relay FR. The first thermal relay FR performs overload detection and transmits the electrical energy to the first motor M1, thereby controlling the start of the first motor M1. The first current transformer PT1 samples the three-phase electrical energy input to the first motor M1. The current is then processed by a first capacitor C1, a second capacitor C2, a second resistor R2, and a first rectifier. T1, the third resistor R3, and the third capacitor C3 are rectified and filtered. When the processed signal exceeds the overload threshold set by the first power supply VCC1, the fourth resistor R4, and the fifth resistor R5, the first comparator A1 outputs a high-level signal, which is the second detection signal. At this time, the first thermal relay FR performs overload protection, controlling the first stationary terminal and the first moving terminal of the first thermal relay switch FR-1 to open, and the second moving terminal and the second stationary terminal of the first thermal relay switch FR-1 to close. The first lighting lamp HL1 is lit. If the first thermal relay switch FR-1 is abnormal and does not respond at this time, the first optocoupler U1 will be cut off, making the A terminal of the first logic chip J1 high. The first logic chip J1 will control the first switch V1 and the second switch V2 to conduct. The first relay K1 is energized and controls the first relay switch K1-1 to open. The first indicator LED1 displays the overload abnormality.
[0052] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention. No reference numerals in the claims should be construed as limiting the scope of the claims.
[0053] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A safety protection circuit for a gantry crane, characterized in that, The safety protection circuit of the gantry crane includes: a power supply module, a motor control module, a motor module, an overload detection module, an alarm detection module, and a protection control module; The power module is used to receive three-phase power, perform short-circuit power outage protection, step down the three-phase power and output the first power. The motor control module is connected to the power supply module and the motor module. It is used to receive the first electrical energy and provide overload power-off protection for the motor module, perform self-locking start control for the motor module, and transmit three-phase electrical energy to the motor module. The motor module is used to receive three-phase electrical energy transmitted by the motor control module and control the gantry crane motor to start; The overload detection module is connected to the motor module and is used to sample and rectify the three-phase power input to the motor control module. When the voltage of the processed signal is greater than the set overload threshold, a second detection signal is output. The alarm detection module is connected to the power supply module and the motor control module. It is used to receive the first electrical energy and output the first detection signal when the motor control module is overloaded and the power is not cut off. When the motor control module performs overload power-off protection, it displays the overload. The protection control module is connected to the alarm detection module and the overload detection module. When it receives the first detection signal and the second detection signal, it displays the overload abnormality and controls the motor control module to stop receiving three-phase power.
2. The safety protection circuit for a gantry crane according to claim 1, characterized in that, The power supply module includes a three-phase power interface, an air switch, a first fuse, a second fuse, a third fuse, and a first transformer; the motor control module includes a first contact switch and a first thermal relay; the motor module includes a first motor; and the overload detection module includes a first current transformer. The first, second, and third terminals of the three-phase power interface are respectively connected to the first stationary terminal, second stationary terminal, and third stationary terminal of the air switch. The first moving terminal of the air switch is connected to the first terminal of the primary side of the first transformer and the first stationary terminal of the first contact switch through a first fuse. The second moving terminal of the air switch is connected to the second stationary terminal of the first contact switch through a second fuse. The third moving terminal of the air switch is connected to the second terminal of the primary side of the first transformer and the third stationary terminal of the first contact switch through a third fuse. The first, second, and third moving terminals of the first contact switch are respectively connected to the first, second, and third terminals of the first thermal relay. The fourth and fifth terminals of the first thermal relay are respectively connected to the first and second terminals of the first motor. The sixth terminal of the first thermal relay is connected to the first terminal of the first current transformer. The second terminal of the first current transformer is connected to the third terminal of the first motor. The first and second terminals of the secondary side of the first transformer are connected to the alarm detection module.
3. The safety protection circuit for a gantry crane according to claim 2, characterized in that, The motor control module further includes a first thermal relay switch, a first push-button switch, a second contact switch, and a first contactor; the protection control module includes a first relay switch. The first stationary terminal and the second stationary terminal of the first thermal relay switch are both connected to the first end of the secondary side of the first transformer. The first moving terminal of the first thermal relay switch is connected to the stationary terminal of the first push-button switch. The moving terminal of the first push-button switch is connected to the stationary terminal of the first relay switch. The moving terminal of the first relay switch is connected to the stationary terminal of the second contact switch and the stationary terminal of the second push-button switch. The moving terminal of the second push-button switch is connected to the stationary terminal of the second contact switch and one end of the first contactor. The other end of the first contactor is connected to the second end of the secondary side of the first transformer. The second moving terminal of the first thermal relay switch is connected to the alarm detection module.
4. The safety protection circuit for a gantry crane according to claim 3, characterized in that, The alarm detection module includes a first resistor, a first diode, a first illumination lamp, and a first optocoupler; The anode of the first diode is connected to the first end of the secondary side of the first transformer through the first resistor. The first end of the first optocoupler is connected to one end of the first lighting lamp. The other end of the first lighting lamp is connected to the second active end of the first thermal relay switch. The second end of the first optocoupler is connected to the second end of the secondary side of the first transformer. The cathode of the first diode is connected to the third end of the first optocoupler and the protection control module. The fourth end of the first optocoupler is grounded.
5. A safety protection circuit for a gantry crane according to claim 4, characterized in that, The overload detection module further includes a first capacitor, a second capacitor, a second resistor, a first rectifier, a third resistor, a third capacitor, a fourth resistor, a fifth resistor, a first power supply, and a first comparator; One end of the first capacitor is connected to the third end of the first current transformer and the first end of the first rectifier, and is connected in sequence to the other end of the first capacitor, the second end of the first rectifier and the fourth end of the first current transformer through the second capacitor and the second resistor. The third end of the first rectifier is connected to one end of the third capacitor and the non-inverting input of the first comparator through the third resistor. The fourth end of the first rectifier is connected to the other end of the third capacitor, one end of the fifth resistor and ground. The other end of the fifth resistor is connected to the inverting input of the first comparator and is connected to the first power supply through the fourth resistor. The output of the first comparator is connected to the protection control module.
6. The safety protection circuit for a gantry crane according to claim 5, characterized in that, The protection control module also includes a first logic chip, a first relay, a first switching transistor, a second switching transistor, a first indicator light, a sixth resistor, and a second power supply; The A and B terminals of the first logic chip are connected to the cathode of the first diode and the output terminal of the first comparator, respectively. The Y terminal of the first logic chip is connected to the base of the first switching transistor and the base of the second switching transistor. The collector of the first switching transistor is connected to one end of the first relay. The other end of the first relay is connected to the second power supply and then connected to the anode of the first indicator light through the sixth resistor. The cathode of the first indicator light is connected to the collector of the second switching transistor. The emitters of the first and second switching transistors are both grounded.