A roll-over ladder system, method and working machine

Abstract

The application discloses a kind of turnover ladder system, method and engineering machinery in the technical field of engineering machinery, to solve the problem that existing technology can only control the turnover of ladder in cab to retract work, when staff get off the car ladder is always in the extended state, cannot be turned over and retracted.It includes walkway and electric control system, the bottom of the walkway is rotatably connected with ladder, the bottom of the walkway is rotatably connected with driving mechanism, the output end of the driving mechanism is rotatably connected with the ladder, the walkway side wall is provided with cab, the first switch is provided on the walkway, the second switch is provided in the cab;The electric control system includes second relay and third relay;The application can operate the turnover of ladder and retract on the ground and walkway without power, the man-machine interaction is high, the operator can avoid being damaged by external collision after getting off the car, to ensure the safety of the device.

Description

Technical Field

[0001] This invention relates to a flip-up ladder system, method, and engineering machinery, belonging to the field of engineering machinery technology. Background Technology

[0002] In recent years, with rapid industrial development and rising labor costs, the market demand for operational efficiency has increased. Large-scale construction machinery is increasingly used in ports, steel mills, and other large construction sites. Simultaneously, the market requires a wider field of vision for equipment, leading to the widespread application of lifting cabs. Because human-machine interaction for operators accessing the cab needs improvement, tilting ladders are typically used to assist in operation. Currently, cab ladders are classified as fixed, hydraulic tilting, and electric tilting. In existing technologies, hydraulic and electric tilting ladders usually only have a tilting control switch installed inside the cab. Fixed cab ladders cannot be tilted and retracted, reducing the equipment's maneuverability and making them susceptible to collision damage. Furthermore, after prolonged high-intensity vibration operation, they are prone to loosening due to being constantly extended, resulting in poor reliability. Hydraulic and electric tilting ladders require the operator to turn on the main power switch, enter the cab, and power on or start the equipment before manually operating the control mechanism to tilt and retract the ladder. Before getting off the vehicle, the extended ladder must be tilted to turn off the engine or turn off the main power switch. Moreover, after getting off the vehicle, the ladder remains in the extended state and cannot be tilted and retracted, making it susceptible to damage from external collisions.

[0003] As can be seen from the above, the existing cab-mounted tilting ladder can usually only be controlled from inside the cab to tilt and retract. When the workers get off the vehicle, the ladder remains in the extended state and cannot be tilted and retracted, making it easy to be damaged by external collisions and affecting the safety of the device. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a flip-up ladder system, method and engineering machinery. Without power, the flip-up extension and retraction of the ladder can be operated from both the ground and the platform. It has high human-machine interaction and can avoid damage to the ladder due to external collisions caused by the operator being unable to flip and retract the ladder after getting off the vehicle, thus ensuring the safety of the device.

[0005] To solve the above-mentioned technical problems, the present invention is implemented using the following technical solution: In a first aspect, the present invention provides a flip-up ladder system, including a platform and an electrical control system. The bottom of the platform is rotatably connected to a ladder, and the bottom of the platform is rotatably connected to a drive mechanism. The output end of the drive mechanism is rotatably connected to the ladder. The side wall of the platform is provided with a driver's cab, the platform is provided with a first switch, and the driver's cab is provided with a second switch. The electronic control system includes a second relay and a third relay; The first switch is connected to the drive mechanism through the second relay and the third relay. The first switch, the second relay and the third relay cooperate to realize the extension and retraction of the drive mechanism. The second switch is connected to the drive mechanism through the second relay and the third relay. The second switch, the second relay and the third relay cooperate to realize the extension and retraction of the drive mechanism.

[0006] Furthermore, the walkway is equipped with a walkway door, which is located on one side of the driver's cab.

[0007] Furthermore, it also includes a lifting mechanism, which is used to lift the cab and the platform.

[0008] Furthermore, the drive mechanism includes a tilting electric cylinder.

[0009] Furthermore, the electronic control system also includes a safety handle and a first relay. The sa terminal of the safety handle is connected to the key switch, the sb terminal of the safety handle is connected to the ka terminal of the first relay, the kc terminal of the first relay is connected to the battery, the kb terminal of the first relay is grounded, the ke terminal of the first relay is connected to the se terminal of the first switch, the sh terminal of the second switch, and the ku terminal of the third relay, respectively, the kd terminal of the first relay is connected to the sc terminal of the first switch, the sf terminal of the second switch, the kn terminal of the second relay, and the kz terminal of the third relay, respectively, the sd terminal of the first switch and the sg terminal of the second switch are both connected to the kj terminal of the second relay, the kl terminal of the second relay is connected to the ma terminal of the drive mechanism, the kk and km terminals of the second relay are both grounded, the kx terminal of the third relay is connected to the mb terminal of the drive mechanism, and the ky and kv terminals of the third relay are both grounded.

[0010] Furthermore, the electronic control system also includes a first limit switch and a second limit switch. The sqa terminal of the first limit switch is connected to the sd terminal of the first switch and the sg terminal of the second switch, respectively. The sqb terminal of the first limit switch is connected to the kj terminal of the second relay. The sqc terminal of the second limit switch is connected to the se terminal of the first switch, the sh terminal of the second switch and the ke terminal of the first relay, respectively. The sqd terminal of the second limit switch is connected to the ku terminal of the third relay.

[0011] Furthermore, the safety handle is a normally open switch.

[0012] Furthermore, the sb terminal of the safety handle is connected to both the signal receiving terminal and the ka terminal of the first relay.

[0013] In a second aspect, the present invention provides a method for flipping a ladder, based on the flipping ladder system described in the first aspect, comprising: Step a: Determine if the key switch is powered on and the safety handle is closed. If yes, proceed to step b; otherwise, proceed to step c. Step b: Connect the kc terminal of the first relay to the ke terminal, and execute step g; Step c: Connect the kc terminal of the first relay to the kd terminal, and then execute step d; Step d: Determine whether the first switch or the second switch is in the ladder extension position. If yes, proceed to step f; otherwise, proceed to step e. Step e: Determine whether the first switch or the second switch is in the ladder retraction position. If yes, proceed to step g; otherwise, proceed to step h. Step f: Determine whether the first limit switch is closed. If yes, control the connection between the kl terminal and the kn terminal of the second relay, and control the connection between the kx terminal and the ky terminal of the third relay. Otherwise, proceed to step h. Step g: Determine whether the second limit switch is closed. If yes, connect the kx terminal of the third relay to the kz terminal and connect the kl terminal of the second relay to the km terminal. Otherwise, proceed to step h. Step h: Connect the kl terminal of the second relay to the km terminal, and connect the kx terminal of the third relay to the ky terminal. The operation is then complete.

[0014] Thirdly, the present invention provides an engineering machine, including the flip-climbing ladder system described in the first aspect.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: 1. This flip ladder system can be operated from both the ground and the walkway to flip, extend, and retract the ladder without power. It has high human-machine interaction and can prevent the ladder from being damaged by external collisions when the operator is unable to flip and retract it after getting off the vehicle, thus ensuring the safety of the device. 2. This tilting ladder system realizes the control system function through a structure of a first switch, a second switch, and a first relay, without the need for a motor controller or other controllers, thus reducing costs. It can achieve zero power consumption when the ladder is stationary, avoiding the depletion of battery power and reducing equipment storage time. The tilting electric cylinder of this application integrates a first limit switch and a second limit switch. When manually tilting and extending or automatically tilting and retracting the ladder, it prevents the tilting electric cylinder drive motor from stalling after reaching the end position, thus preventing damage to the tilting electric cylinder drive motor. 3. With this flip ladder method, after the equipment is powered on and the safety handle is opened, it is forbidden to manually flip the ladder. If the operator forgets to flip and retract the ladder during operation, the system can automatically flip and retract the ladder into place, preventing problems such as misoperation, collision damage, excessive noise, and loose ladder during equipment operation. Attached Figure Description

[0016] Figure 1 This is a three-dimensional structural diagram of a flip ladder system with the ladder extended according to an embodiment of the present invention; Figure 2 This is a three-dimensional structural diagram of a flip-up ladder system when the ladder is retracted, according to an embodiment of the present invention. Figure 3 This is a connection diagram of an electronic control system provided according to an embodiment of the present invention; Figure 4 This is a flowchart illustrating a flipping ladder climbing method provided by an embodiment of the present invention.

[0017] In the diagram: 1. Ladder; 2. Drive mechanism; 3. First switch; 4. Platform; 5. Second switch; 6. Lifting mechanism; 7. Driver's cab; 8. Platform door; 9. Safety handle; 10. First relay; 11. Second relay; 12. Third relay; 201. First limit switch; 202. Second limit switch. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0019] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances. Example 1:

[0021] like Figures 1-2 As shown, the present invention provides a flip ladder system, including a platform 4 and an electrical control system. The bottom of the platform 4 is rotatably connected to a ladder 1, and the bottom of the platform 4 is rotatably connected to a drive mechanism 2. The output end of the drive mechanism 2 is rotatably connected to the ladder 1. The side wall of the platform 4 is provided with a driver's cab 7. The platform 4 is provided with a first switch 3, and the driver's cab 7 is provided with a second switch 5. The electronic control system includes a second relay 11 and a third relay 12; The first switch 3 is connected to the drive mechanism 2 through the second relay 11 and the third relay 12. The first switch 3, the second relay 11 and the third relay 12 cooperate to realize the extension and retraction of the drive mechanism 2. The second switch 5 is connected to the drive mechanism 2 through the second relay 11 and the third relay 12. The second switch 5, the second relay 11 and the third relay 12 cooperate to realize the extension and retraction of the drive mechanism 3.

[0022] Specifically, the first switch 3 is installed on the walkway 4, which is accessible to the worker from the ground. During operation, when the worker needs to climb into the cab 7, the first switch 3 controls the drive mechanism 2 to start working. The drive mechanism 2 pushes the ladder 1 to rotate, extending the ladder 1 to a vertical position for the worker to climb. When the worker is in the cab 7, the first switch 3 or the second switch 5 controls the drive mechanism 2 to rotate the ladder 1 back to its original position, thus retracting the ladder 1 in time. When the worker controls the drive mechanism 2 to extend the ladder 1 to a vertical position and returns to the ground from the cab 7, the first switch 3 controls the drive mechanism 2 to return the ladder 1 to its original position, completing the retraction of the ladder 1. This prevents the ladder 1 from being constantly extended, thus avoiding damage from external collisions and ensuring the safety of the device.

[0023] This invention allows the ladder 1 to be rotated, extended, and retracted from both the ground and the platform 4 without power, providing high human-machine interaction. It also prevents damage to the ladder 1 caused by external collisions due to the operator being unable to rotate and retract it after getting off the vehicle, thus ensuring the safety of the device.

[0024] In this embodiment, the platform 4 is provided with a platform door 8, which is located on one side of the cab 7; it also includes a lifting mechanism 6, which is used to drive the cab 7 and the platform 4 to lift. Optionally, the lifting mechanism 6 is installed behind the cab; the drive mechanism 2 includes a tilting electric cylinder. Optionally, the drive mechanism 2 can also be a hydraulic cylinder, pneumatic cylinder, or other similar power structure.

[0025] like Figure 3 As shown, in this embodiment, the electronic control system further includes a safety handle 9 and a first relay 10. The sa terminal of the safety handle 9 is connected to the key switch, the sb terminal of the safety handle 9 is connected to the ka terminal of the first relay 10, the kc terminal of the first relay 10 is connected to the battery, the kb terminal of the first relay 10 is grounded, the ke terminal of the first relay 10 is connected to the se terminal of the first switch 3, the sh terminal of the second switch 5, and the ku terminal of the third relay 12, respectively, the kd terminal of the first relay 10 is connected to the sc terminal of the first switch 3, the sf terminal of the second switch 5, the kn terminal of the second relay 11, and the kz terminal of the third relay 12, respectively, the sd terminal of the first switch 3 and the sg terminal of the second switch 5 are both connected to the kj terminal of the second relay 11, and the second relay 1... The kl terminal of the first relay 11 is connected to the ma terminal of the drive mechanism 2. The kk and km terminals of the second relay 11 are both grounded. The kx terminal of the third relay 12 is connected to the mb terminal of the drive mechanism 2. The ky and kv terminals of the third relay 12 are both grounded. The electronic control system also includes a first limit switch 201 and a second limit switch 202. The sqa terminal of the first limit switch 201 is connected to the sd terminal of the first switch 3 and the sg terminal of the second switch 5, respectively. The sqb terminal of the first limit switch 201 is connected to the kj terminal of the second relay 11. The sqc terminal of the second limit switch 202 is connected to the se terminal of the first switch 3, the sh terminal of the second switch 5 and the ke terminal of the first relay 10, respectively. The sqd terminal of the second limit switch 202 is connected to the ku terminal of the third relay 12.

[0026] Specifically, the safety handle 9 is a normally open switch used to control the on / off of the pilot main oil circuit and to switch the flipping operation mode of the ladder 1; the control coil of the first relay 10 has ka and kb terminals, the common terminal of the normally open and normally closed contacts is kc, the other end of the normally closed contact is kd, and the other end of the normally open contact is ke. The normally closed contact is used to manually operate the power supply of the electrical control system, and the normally open contact is used to automatically control the flipping and retraction of the ladder 1.

[0027] Optionally, the common end of the ladder extension and retraction positions of the first switch 3 is the SC end, the other end of the ladder extension position is the SD end, and the other end of the ladder retraction position is the SE end; the common end of the ladder extension and retraction positions of the second switch 5 is the SF end, the other end of the ladder extension position is the SG end, and the other end of the ladder retraction position is the SH end; the first switch 3 and the second switch 5 are used to manually operate the ladder 1 to flip and extend and retract, realizing the control of the ladder 1 to flip and extend and retract from two locations.

[0028] The control coil of the second relay 11 has two terminals, kj and kk, and the common terminal of the normally open and normally closed contacts is kl. The other end of the normally closed contact is km, and the other end of the normally open contact is kn. The control coil of the third relay 12 has two terminals: ku and kv. The common terminal of the normally open and normally closed contacts is kx. The other end of the normally closed contact is ky, and the other end of the normally open contact is kz. The first limit switch 201 is the extension limit switch of the tilting electric cylinder, normally closed, with terminals sqa and sqb respectively. The second limit switch 202 is the retraction limit switch of the tilting electric cylinder, normally closed, with terminals sqc and sqd respectively. The first limit switch 201 and the second limit switch 202 are integrated and installed inside the tilting electric cylinder. The tilting electric cylinder is used to drive the tilting extension and retraction of the ladder 1, with terminals ma and mb respectively.

[0029] Optional, Figure 3In this diagram, IG represents the key switch, and B+ represents the battery. The SB terminal of the safety handle 9 is connected to both the signal receiver and the Ka terminal of the first relay 10. After the key switch connected to the SA terminal of the safety handle 9 is powered on, the SB terminal transmits the safety handle status signal to the engineering machinery equipment control system through the signal receiver. The Ka terminal of the first relay 10 and the safety handle status signal receiver are connected in parallel to the SB terminal of the safety handle 9. The KB terminal is connected to the power ground, and the KC terminal is connected to the positive terminal of the battery. The SC terminal of the first switch 3, the SF terminal of the second switch 5, the KN terminal of the second relay 11, and the KZ terminal of the third relay 12 are connected in parallel to the first relay 10. The first relay 10's KD terminal, the first switch 3's SE terminal, and the second switch 5's SH terminal are connected in parallel to the second limit switch 202's SQC terminal; the first switch 3's SD terminal and the second switch 5's SG terminal are connected in parallel to the first limit switch 201's SQA terminal; the second relay 11's KJ terminal is connected to the first limit switch 201's SQB terminal, its KK and KM terminals are connected to the power supply ground, and its KL terminal is connected to the tilting electric cylinder's MA terminal; the third relay 12's KU terminal is connected to the second limit switch 202's SQD terminal, its KV and KY terminals are connected to the power supply ground, and its KX terminal is connected to the tilting electric cylinder's MB terminal.

[0030] Optionally, the first switch 3 and the second switch 5 can be replaced by different forms such as self-resetting rocker switches, self-resetting rotary switches, and self-resetting push-button switches, with similar functions. In addition, the two-location control in this system can achieve the function of multi-location control by continuing to connect the control components in parallel. Optionally, the first limit switch 201 and the second limit switch 202 integrated in the tilting electric cylinder can be changed to externally mounted limit switches, or different forms such as proximity switches + relays, with similar functions. The safety handle 9 can be replaced by different forms of equipment preparation status signals + controllers, such as total pilot oil pressure value, engine speed value, and working mode. Multiple relays can be replaced by high-power transistors or MOSFETs.

[0031] This invention realizes the control system function through the structure of the first switch 3, the second switch 5 and the first relay 10, etc., without the need for a motor controller and other controllers, which is low in cost. It can achieve zero power consumption when the ladder 1 is in a stationary state, avoiding the loss of battery power and reducing the equipment storage time. The flipping electric cylinder of this application integrates the first limit switch 201 and the second limit switch 202. When manually flipping and extending or automatically flipping and retracting the ladder 1, it prevents the flipping electric cylinder drive motor from stalling after it is in place, thus preventing damage to the flipping electric cylinder drive motor. Example 2:

[0032] like Figure 4As shown, the present invention provides a flip-climbing ladder method, based on the flip-climbing ladder system described in Embodiment 1, comprising: Step a: Determine if the key switch is powered on and the safety handle 9 is closed. If yes, proceed to step b; otherwise, proceed to step c. Step b: Connect the kc terminal of the first relay 10 to the ke terminal, and execute step g; Step c: Connect the kc terminal of the first relay 10 to the kd terminal, and execute step d; Step d: Determine whether the first switch 3 or the second switch 5 is in the ladder extension position. If yes, proceed to step f; otherwise, proceed to step e. Step e: Determine whether the first switch 3 or the second switch 5 is in the ladder retraction position. If yes, proceed to step g; otherwise, proceed to step h. Step f: Determine whether the first limit switch 201 is closed, i.e. whether the ladder 1 has not yet flipped and extended to the full position. If so, control the connection between the kl terminal and the kn terminal of the second relay 11, energize the ma terminal of the flipping cylinder, control the connection between the kx terminal and the ky terminal of the third relay 12, and connect the mb terminal to the power ground through the third relay 12, so that the flipping cylinder extends and further drives the ladder 1 to flip and extend. Otherwise, execute step h. Step g: Determine whether the second limit switch 202 is closed, i.e. whether the ladder 1 has not yet flipped and retracted to the correct position. If so, control the connection between the kx and kz terminals of the third relay 12, energize the mb terminal of the flipping cylinder, control the connection between the kl and km terminals of the second relay 11, and connect the ma terminal to the power ground through the second relay 11, so that the flipping cylinder retracts and further drives the ladder 1 to flip and retract. Otherwise, proceed to step h. Step h: The coils of the second relay 11 and the third relay 12 are both de-energized. The kl terminal of the second relay 11 is connected to the km terminal, and the kx terminal of the third relay 12 is connected to the ky terminal. The ma terminal of the tilting cylinder is connected to the power ground, and the mb terminal of the tilting cylinder is connected to the power ground. The tilting cylinder does not work, the ladder 1 remains stationary, and the work ends.

[0033] Optional, Figure 4 Relay I is the first relay 10, relay II is the second relay 11, relay III is the third relay 12, switch I is the first switch 3, switch II is the second switch 5, limit switch I is the first limit switch 201, and limit switch I is the second limit switch 202.

[0034] This invention prevents manual flipping of ladder 1 after the equipment is powered on and safety handle 9 is opened. If the operator forgets to flip and retract ladder 1 during operation, the system can automatically flip and retract ladder 1 into place, preventing problems such as misoperation, collision damage, excessive noise, and loose ladder 1 during equipment operation. Example 3:

[0035] The present invention provides an engineering machine, including the flipping ladder system described in Embodiment 1.

[0036] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A flip-up ladder system, characterized in that, The system includes a walkway and an electrical control system. A ladder is rotatably connected to the bottom of the walkway, and a drive mechanism is rotatably connected to the bottom of the walkway. The output end of the drive mechanism is rotatably connected to the ladder. A driver's cab is provided on the side wall of the walkway. A first switch is provided on the walkway, and a second switch is provided in the driver's cab. The electronic control system includes a second relay and a third relay; The first switch is connected to the drive mechanism through the second relay and the third relay. The first switch, the second relay and the third relay cooperate to realize the extension and retraction of the drive mechanism. The second switch is connected to the drive mechanism through the second relay and the third relay. The second switch, the second relay and the third relay cooperate to realize the extension and retraction of the drive mechanism.

2. The flip-up ladder system according to claim 1, characterized in that, The walkway is equipped with a walkway door, which is located on one side of the driver's cab.

3. The flip-up ladder system according to claim 1, characterized in that, It also includes a lifting mechanism, which is used to lift the cab and the platform.

4. The flip-up ladder system according to claim 1, characterized in that, The drive mechanism includes a tilting electric cylinder.

5. The flip-up ladder system according to claim 1, characterized in that, The electronic control system also includes a safety handle and a first relay. The sa terminal of the safety handle is connected to the key switch, the sb terminal of the safety handle is connected to the ka terminal of the first relay, the kc terminal of the first relay is connected to the battery, the kb terminal of the first relay is grounded, the ke terminal of the first relay is connected to the se terminal of the first switch, the sh terminal of the second switch, and the ku terminal of the third relay, respectively, the kd terminal of the first relay is connected to the sc terminal of the first switch, the sf terminal of the second switch, the kn terminal of the second relay, and the kz terminal of the third relay, respectively, the sd terminal of the first switch and the sg terminal of the second switch are both connected to the kj terminal of the second relay, the kl terminal of the second relay is connected to the ma terminal of the drive mechanism, the kk and km terminals of the second relay are both grounded, the kx terminal of the third relay is connected to the mb terminal of the drive mechanism, and the ky and kv terminals of the third relay are both grounded.

6. The flip-up ladder system according to claim 5, characterized in that, The electronic control system further includes a first limit switch and a second limit switch. The sqa terminal of the first limit switch is connected to the sd terminal of the first switch and the sg terminal of the second switch, respectively. The sqb terminal of the first limit switch is connected to the kj terminal of the second relay. The sqc terminal of the second limit switch is connected to the se terminal of the first switch, the sh terminal of the second switch and the ke terminal of the first relay, respectively. The sqd terminal of the second limit switch is connected to the ku terminal of the third relay.

7. The flip-up ladder system according to claim 5, characterized in that, The safety handle is a normally open switch.

8. The flip-up ladder system according to claim 5, characterized in that, The sb terminal of the safety handle is connected to the signal receiving terminal and the ka terminal of the first relay, respectively.

9. A method for flipping a ladder, based on the flipping ladder system of claim 6, characterized in that, include: Step a: Determine if the key switch is powered on and the safety handle is closed. If yes, proceed to step b; otherwise, proceed to step c. Step b: Connect the kc terminal of the first relay to the ke terminal, and execute step g; Step c: Connect the kc terminal of the first relay to the kd terminal, and then execute step d; Step d: Determine whether the first switch or the second switch is in the ladder extension position. If yes, proceed to step f; otherwise, proceed to step e. Step e: Determine whether the first switch or the second switch is in the ladder retraction position. If yes, proceed to step g; otherwise, proceed to step h. Step f: Determine whether the first limit switch is closed. If yes, control the connection between the kl terminal and the kn terminal of the second relay, and control the connection between the kx terminal and the ky terminal of the third relay. Otherwise, proceed to step h. Step g: Determine whether the second limit switch is closed. If yes, connect the kx terminal of the third relay to the kz terminal and connect the kl terminal of the second relay to the km terminal. Otherwise, proceed to step h. Step h: Connect the kl terminal of the second relay to the km terminal, and connect the kx terminal of the third relay to the ky terminal. The operation is then complete.

10. An engineering machinery, characterized in that, Includes the flip ladder system as described in any one of claims 1 to 8.

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