PLC automatic control double-limiting tray lifting conveyor

Abstract

This invention relates to the field of conveyors, and in particular to a PLC-controlled double-limit pallet lifting conveyor, comprising a body for carrying empty pallets; a cylinder and a gantry frame fixedly mounted on the body; and a feeding mechanism disposed between the body and the gantry frame. The feeding mechanism includes a lifting component and a control component connected to the output end of the cylinder. The control component controls the lifting component to first extend under the second-to-last empty pallet, and then lift the second-to-last and subsequent empty pallets. It also includes a conveying component and an association component. The association component moves with the control component and, after the second-to-last and subsequent empty pallets are lifted, rolls to lift and push the lowest empty pallet. By using a single cylinder as the sole power source, and cooperating with the wedge-shaped transmission between the control component and the lifting component, the material distribution sequence of the lifting plate first horizontally extending into the pallet gap, and then vertically lifting to isolate the upper pallet is fixed.

Description

Technical Field

[0001] This invention relates to the field of conveyors, and in particular to a PLC-controlled double-limit pallet lifting conveyor. Background Technology

[0002] In the pallet circulation feeding process of automated production lines and intelligent warehousing and sorting systems, the layering, lifting, isolation, and single-pallet conveying of stacked empty pallets are the core processes for achieving continuous automated operation of the production line. Currently, conventional pallet lifting and conveying equipment in the industry generally adopts a multi-set independent drive cylinder design, meaning that the layering, lifting, isolation, and single-pallet conveying of empty pallets are all independently controlled. Simultaneously, to support stacked pallets, the machine body is often equipped with normally closed roller groups and independent locking mechanisms. These lock the rollers when pallets are stacked and switch to free-rolling mode when pallets are pushed out, thus adapting to the requirements of the material distribution and conveying processes. However, current pallet lifting and conveying systems still have certain shortcomings: Firstly, the separate control design of multiple independent cylinders requires extremely high precision in the coordination and timing of actions between multiple mechanisms. Therefore, in order to avoid mechanical interference when multiple independent cylinders operate, sufficient safety margin and signal waiting time must be reserved between the start and stop actions of each cylinder. This results in inherent pauses at the connection points of the material distribution, lifting, and conveying processes, which lengthens the cycle time of single pallet conveying. Under the high-frequency and continuous material supply requirements of the production line, the continuous accumulation of pause time will directly and significantly reduce the efficiency of pallet conveying, making it difficult to adapt to the application requirements of high-cycle automated production lines. Summary of the Invention

[0003] In view of the inherent pauses at the connection points of the material sorting, lifting, and conveying processes in the above-mentioned or existing technologies, this invention is proposed.

[0004] Therefore, the purpose of this invention is to provide a PLC-controlled dual-limit pallet lifting conveyor.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A PLC-controlled dual-limit pallet lifting conveyor includes, The body used to carry empty pallets; Cylinders and gantry frames are fixedly mounted on the machine body; A feeding mechanism is disposed between the machine body and the gantry frame, the feeding mechanism including... The lifting assembly and the control assembly connected to the cylinder output end, wherein the control assembly is used to control the lifting assembly to first extend under the second-to-last empty pallet, and then lift the second-to-last and above empty pallets; The conveying component and the associated component move with the control component and, after the second-to-last or higher empty pallet is lifted, roll up and push the lowest empty pallet.

[0006] As a preferred embodiment of the PLC-controlled dual-limit pallet lifting conveyor of the present invention, the lifting assembly includes several fixed plates fixedly installed on the gantry frame, guide rods are fixedly installed between the fixed plates and the gantry frame, and a lifting frame is slidably installed on the outer side of the several guide rods.

[0007] As a preferred embodiment of the PLC-controlled dual-limit pallet lifting conveyor of the present invention, wherein: a mounting frame is fixedly installed on the lifting frame, and a plurality of return springs are fixedly installed on the mounting frame, and a return plate is installed at the ends of the plurality of return springs.

[0008] As a preferred embodiment of the PLC-controlled dual-limit pallet lifting conveyor of the present invention, wherein: a limit rod of a sliding through-mounting frame is fixedly installed on the reset plate, and a lifting plate is fixedly installed at the end of the limit rod.

[0009] As a preferred embodiment of the PLC-controlled dual-limit pallet lifting conveyor of the present invention, the control component includes a control frame fixedly installed on the outside of the cylinder output shaft, a plurality of control boards fixedly installed on the control frame, and a wedge-shaped frame that cooperates with the corresponding control board fixedly installed on the reset plate.

[0010] As a preferred embodiment of the PLC-controlled dual-limit pallet lifting conveyor of the present invention, the control board is provided with a protrusion, and the reset plate is provided with an inclined surface that cooperates with the wedge shape of the protrusion.

[0011] As a preferred embodiment of the PLC-controlled dual-limit pallet lifting conveyor of the present invention, the conveying assembly includes a support plate fixedly installed on the inner wall of the machine body, an mounting plate slidably installed on the support plate via several sliding rods, a roller assembly fixedly installed on the mounting plate, and several openings corresponding to the roller assembly on the upper surface of the machine body.

[0012] As a preferred embodiment of the PLC-controlled dual-limit pallet lifting conveyor of the present invention, wherein: a push plate is fixedly installed at the output end of the cylinder, and the push plate is used to push empty pallets.

[0013] As a preferred embodiment of the PLC-controlled dual-limit pallet lifting conveyor of the present invention, the associated component includes several grooves formed on the machine body, and wedge blocks are fixedly installed on the control board through a connecting frame, with several wedge blocks connected to each other through a connecting plate.

[0014] As a preferred embodiment of the PLC-controlled dual-limit pallet lifting conveyor of the present invention, a wedge plate is installed at the end of the corresponding slide bar, and the wedge block and the corresponding wedge plate are wedge-shaped.

[0015] The beneficial effects of the PLC-controlled dual-limit pallet lifting conveyor of the present invention are as follows: In this application, a single cylinder is used as the sole power source, in conjunction with the wedge-shaped transmission of the control and lifting components. This solidifies the material distribution sequence where the lifting plate first extends horizontally into the pallet gap and then vertically lifts to isolate the upper pallet. Simultaneously, through the associated components that are synchronously linked with the cylinder, the vertical lifting action of the roller group of the conveying component is automatically triggered after the material distribution action is completed. This, in turn, works with the push plate at the end of the cylinder to smoothly push the bottom pallet out. The entire process of material distribution, lifting, hoisting, and conveying is seamlessly connected, completely eliminating the safety margin and action waiting pauses that must be reserved to avoid mechanical interference in existing multi-cylinder control schemes. This significantly reduces the cycle time of single-pallet conveying, fundamentally solving the problem of low conveying efficiency caused by the accumulation of action pause time. It is suitable for the continuous material supply requirements of high-cycle automated production lines, and greatly improves conveying efficiency and stability. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a three-dimensional structural diagram of the present invention.

[0018] Figure 2 This is a three-dimensional structural diagram of the gantry and cylinder parts of the present invention.

[0019] Figure 3 This is a three-dimensional structural diagram of the control board and wedge frame of the present invention.

[0020] Figure 4 This is a three-dimensional structural diagram of the fixing plate and guide rod of the present invention.

[0021] Figure 5 This is an exploded view of the three-dimensional structure of the lifting component of the present invention.

[0022] Figure 6 This is a three-dimensional structural diagram of the connecting frame, wedge block, and connecting plate of the present invention.

[0023] Figure 7 This is a three-dimensional structural diagram of a portion of the lifting frame, mounting frame, and return spring of the present invention.

[0024] In the diagram: 1. Machine body; 2. Empty pallet; 3. Feeding mechanism; 4. Gantry frame; 5. Cylinder; 31. Lifting assembly; 311. Fixing plate; 312. Guide rod; 313. Lifting frame; 314. Mounting frame; 315. Return spring 1; 316. Return plate; 317. Lifting plate; 318. Limit rod; 32. Control assembly; 321. Control frame; 322. Control board; 323. Wedge frame; 324. Inclined surface; 33. Conveying assembly; 331. Support plate; 332. Mounting plate; 333. Roller assembly; 334. Push plate; 335. Slide rod; 34. Associated assembly; 341. Slide groove; 342. Wedge plate; 343. Connecting frame; 344. Wedge block; 345. Connecting plate. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0026] Reference Figure 1 , Figure 2 and Figure 3 This embodiment provides a PLC-controlled dual-limit pallet lifting conveyor that can achieve seamless connection of material distribution, lifting, jacking, and conveying actions throughout the entire process. It includes a body 1 for carrying empty pallets 2; a cylinder 5 and a gantry frame 4 fixedly installed on the body 1; and a feeding mechanism 3 located between the body 1 and the gantry frame 4. The feeding mechanism 3 includes a lifting component 31 and a control component 32 connected to the output end of the cylinder 5. The control component 32 controls the lifting component 31 to first extend under the second-to-last empty pallet 2, and then lift the second-to-last and subsequent empty pallets 2. It also includes a conveying component 33 and an association component 34. The association component 34 moves with the control component 32 and, after the second-to-last and subsequent empty pallets 2 are lifted, rolls to lift and push the lowest empty pallet 2.

[0027] It should be noted that the stacked empty pallets 2 are placed vertically on the surface of the machine body 1; the discharge end of the empty pallets 2 is connected to the automated production line that requires the empty pallets 2 to be supplied; this conveyor uses the PLC controller built into the machine body 1 as the core control center, the control end of the electromagnetic reversing valve of the cylinder 5 is electrically connected to the digital output port of the PLC controller, the stroke sensors on the cylinder body corresponding to reset and conveying to the position, and the signal output ends of the pallet position detection and discharge position detection sensors on the machine body 1 are all electrically connected to the digital input port of the PLC controller; the PLC controller collects the real-time status signals of each sensor and combines them with the preset action timing logic to control the extension, retraction and start / stop of the cylinder 5, so as to realize the automated closed-loop control of the entire process of pallet layer lifting and conveying; the above-mentioned PLC controller, cylinder 5, various sensing elements and their supporting electrical control principles are all existing technologies, so they will not be described in detail in this application.

[0028] Reference Figure 1 , Figure 2 , Figure 4 and Figure 7 The number of gantry frames 4 is two, and the two gantry frames 4 are symmetrical to each other along the length direction of the empty pallet 2. The lifting assembly 31 includes two fixed plates 311 that are fixedly installed on the gantry frames 4 and are symmetrical to each other along the length direction of the empty pallet 2. A guide rod 312 is fixedly installed between the fixed plate 311 and the gantry frame 4. A lifting frame 313 is slidably installed on the outer side of the two guide rods 312.

[0029] Reference Figure 1 , Figure 2 , Figure 4 and Figure 7 The lifting frame 313 is fixedly installed with a mounting frame 314 on the side near the machine body 1. A plurality of return springs 315 are fixedly installed on the mounting frame 314. The ends of the plurality of return springs 315 are jointly installed with a return plate 316. A limiting rod 318 that slides through the mounting frame 314 is fixedly installed on the side of the return plate 316 near the mounting frame 314. A lifting plate 317 is fixedly installed at the end of the limiting rod 318.

[0030] It should be noted that the guide rod 312 provides guidance for the vertical movement of the lifting frame 313. Together with the two sets of symmetrically arranged lifting components 31, it ensures that the lifting frames 313 on both sides can achieve completely synchronous lifting and lowering, avoiding height differences in the lifting plate 317, and thus preventing the problem of the upper empty pallet 2 being lifted off-center or falling off. When the return spring 315 is in the naturally extended state, the lifting plate 317 is in the horizontally retracted state. At this time, the lifting plate 317 does not extend into the bottom gap of the second to last empty pallet 2, providing a spatial basis for the stacking of the empty pallets 2.

[0031] Reference Figure 3 , Figure 4 , Figure 6 and Figure 7 The control component 32 includes a control frame 321 fixedly installed on the outside of the output shaft of the cylinder 5. Two control plates 322 symmetrical to each other along the conveying direction of the empty tray 2 are fixedly installed on the control frame 321. A wedge-shaped frame 323 that wedges with the corresponding control plate 322 is fixedly installed on the side of the reset plate 316 near the machine body 1.

[0032] Reference Figure 3 , Figure 4 , Figure 6 and Figure 7 The control plate 322 is provided with a protrusion, and the reset plate 316 is provided with an inclined surface 324 that cooperates with the wedge shape of the protrusion on the side near the cylinder 5.

[0033] It should be noted that the control frame 321 is rigidly connected to the output shaft of the cylinder 5, and the control plate 322 can move horizontally and reciprocally with the output shaft of the cylinder 5. The wedge-shaped fit between the control plate 322 and the wedge-shaped fit between the protrusion on the control plate 322 and the wedge-shaped fit between the inclined surface 324 of the reset plate 316 can decompose the horizontal linear thrust of the cylinder 5 into the thrust of the lifting plate 317 approaching the empty pallet 2 and the vertical upward lifting force. Through the stroke coordination of the mechanical structure, the fixed action sequence of the lifting plate 317 first extending horizontally and then lifting vertically is realized. No additional control elements and timing programming are required. The action logic is stable and avoids the risk of incorrect timing of the material distribution action.

[0034] In practical use, when there is no demand for empty pallet 2 to be supplied by the automated production line connected to the empty pallet 2 discharge end, the machine body 1 is in a stable standby state under the control of the PLC controller. The output shaft of the cylinder 5 is fully retracted to the initial position. At this time, the reset spring 315 remains in a naturally extended state. Through the reset plate 316 and the limit rod 318, the lifting plate 317 is driven to maintain the initial horizontal retraction position. The lifting plate 317 is completely removed from the empty pallet 2 stacking station range, and will not cause any structural interference to the stacking and natural falling of the empty pallets 2. At the same time, the lifting frame 313 falls to the lowest position of the vertical stroke along the guide rod 312. The top surface height of the lifting plate 317 is lower than the bottom edge height of the second to last empty pallet 2, which reserves the action space for the subsequent horizontal extension and lifting action of the lifting plate 317.

[0035] Meanwhile, the stacked empty pallets 2 are vertically placed on the surface of the machine body 1, waiting for the feeding command to be triggered. When the automated production line station sends a feeding demand signal for the empty pallets 2, the signal is transmitted to the PLC controller built into the machine body 1. The PLC controller immediately outputs a control command, controlling the output shaft of the cylinder 5 to extend forward along the conveying direction of the empty pallets 2. As the cylinder 5 extends, it simultaneously drives the control frame 321 and the control plate 322 to move at the same speed. During the continuous forward extension of the cylinder 5, the control plate 322 first squeezes the wedge frame 323 and wedges with the wedge frame 323. At this time, the horizontal linear thrust output by the cylinder 5 is decomposed into a horizontal force through the wedge transmission, thereby driving the reset plate 316 to overcome the elastic force of the reset spring 315 and drive the lifting plate 317 to extend horizontally towards the stacked empty pallets 2 and insert into the gap between the second to last empty pallet 2 and the bottom empty pallet 2.

[0036] Next, cylinder 5 continues to extend forward, and the protrusion of control plate 322 begins to apply a pushing force to the inclined surface 324 on reset plate 316. The force generated by the wedge engagement is converted into a vertically upward lifting force, thereby driving the lifting frame 313 to move vertically upward along guide rod 312. The vertical lifting of lifting frame 313 simultaneously drives the lifting plate 317 to lift upward, and then the lifting plate 317 lifts all the stacked empty pallets 2 from the second to last and above upward as a whole, so that the upper empty pallet 2 is completely separated from the lowermost empty pallet 2, forming a stable material distribution gap, and completing the layering and material distribution action of stacked empty pallets 2. After that, the output end of cylinder 5 continues to move, the top surface of the protrusion of control plate 322 slides and engages with the bottom surface of reset plate 316, and the side surface of control plate 322 slides and engages with the side surface of reset plate 316, forming a mechanical lock on the horizontal and vertical positions of lifting plate 317.

[0037] Reference Figure 3 , Figure 4 , Figure 6 and Figure 7 The conveying assembly 33 includes a support plate 331 fixedly installed on the inner wall of the machine body 1. An mounting plate 332 is slidably installed on the support plate 331 via several sliding rods 335. A roller assembly 333 is fixedly installed on the mounting plate 332. Several openings corresponding to the roller assembly 333 are opened on the upper surface of the machine body 1.

[0038] Reference Figure 3 , Figure 4 , Figure 6 and Figure 7 A push plate 334 is fixedly installed at the output end of the cylinder 5, and the push plate 334 is used to push the empty pallet 2.

[0039] It should be noted that the slide bar 335 provides guidance for the vertical lifting and lowering of the mounting plate 332 and the roller assembly 333, ensuring the horizontality of the roller assembly 333 during the lifting and lowering process. In the natural standby state, the top surface of the roller assembly 333 is lower than the upper surface of the body 1, so that the bottom empty tray 2 can be stably placed on the upper surface of the body 1. The openings on the upper surface of the body 1 correspond one-to-one with the individual rollers of the roller assembly 333, ensuring that when the roller assembly 333 moves upward, it can smoothly pass through the openings and extend out of the upper surface of the body 1, thereby lifting the bottom empty tray 2 upward. This design ensures that the bottom empty pallet 2 is completely disconnected from the upper surface of the machine body 1, converting the sliding friction of the bottom empty pallet 2 during the pushing process into the rolling friction of the roller. This significantly reduces the running resistance of the pusher plate 334 when pushing the empty pallet 2, reducing wear on the surface of the empty pallet 2 and the load on the cylinder 5, thus improving the smoothness of the pushing action. The pushing surface of the pusher plate 334 corresponds perfectly to the side of the empty pallet 2, ensuring that the pushing force can be evenly applied to the side of the empty pallet 2, preventing the empty pallet 2 from tilting during the pushing process and ensuring conveying accuracy.

[0040] Reference Figure 3 , Figure 4 , Figure 6 and Figure 7 The associated component 34 includes two symmetrical grooves 341 formed on the body 1 and along the conveying direction of the empty pallet 2. A wedge block 344 is fixedly installed on the control board 322 by a connecting frame 343, and the two wedge blocks 344 are connected by a connecting plate 345.

[0041] Reference Figure 3 , Figure 4 , Figure 6 and Figure 7 The corresponding slide rod 335 has a wedge plate 342 installed at its end, and the wedge block 344 is wedge-shaped and engages with the corresponding wedge plate 342.

[0042] It should be noted that the connecting frame 343 is installed through the slide groove 341 and can slide horizontally along the length of the slide groove 341, providing guidance for the horizontal movement of the connecting frame 343; the wedge block 344 and the inclined surface 324 of the wedge plate 342 fit together to form a wedge fit, and the triggering time of this wedge fit is later than the triggering time of the fit between the control component 32 and the lifting component 31, that is: when the cylinder 5 extends, the lifting and distributing action of the upper empty pallet 2 must be completed by the control component 32 first, and then the wedge block 344... Only when the wedge block 344 contacts the wedge plate 342 will it trigger the lifting action, thus ensuring the action sequence of material separation first and then conveying, avoiding the timing conflict of pushing the bottom empty pallet 2 before it is separated; when the material separation is completed, as the wedge block 344 continues to move forward with the cylinder 5, the horizontal thrust of the cylinder 5 is converted into a vertical upward lifting force through the wedge engagement, driving the wedge plate 342, slide rod 335, mounting plate 332 and roller group 333 to move upward synchronously, realizing the lifting action of the bottom empty pallet 2.

[0043] In actual use, in standby mode, the connecting frame 343 and the wedge block 344 are on the side away from the wedge plate 342, and the wedge block 344 is completely disengaged from the wedge plate 342 without any transmission cooperation; the slide rod 335, the mounting plate 332, and the roller assembly 333 are at the lowest position of their vertical stroke under their own gravity, and the top surface of the roller assembly 333 is lower than the upper surface of the machine body 1. The bottommost pallet of the stacked empty pallets 2 is completely attached to and stably placed on the upper surface of the machine body 1; at the same time, the push plate 334 retracts with the cylinder 5, completely avoiding the stacking space of the empty pallets 2, without affecting the stacking and positioning of the empty pallets 2.

[0044] When the lifting and material distribution action is fully completed, the horizontal stroke of the lifting plate 317 is mechanically locked, the upper empty pallet 2 is lifted into place, and the lower empty pallet 2 is completely separated from the upper empty pallet 2, the cylinder 5 continues to extend forward. At this time, the wedge block 344 continues to move synchronously with the control plate 322 and will squeeze the wedge plate 342. The horizontal linear thrust continuously output by the cylinder 5 is converted into a vertical upward component force through the cooperation of the wedge block 344 and the inclined surface 324 of the wedge plate 342. This force overcomes the weight of the roller assembly 333, the mounting plate 332 and the slide rod 335, and pushes the wedge plate 342 upward. This causes the roller assembly 333 to be lifted upward, slightly lifting the lower empty pallet 2 that has been separated from the upper layer, so that the bottom surface of the empty pallet 2 is no longer in contact with the upper surface of the machine body 1.

[0045] After the roller assembly 333 completely lifts the bottom empty pallet 2, the cylinder 5 continues to extend forward, and the push plate 334 will fully contact the side of the bottom empty pallet 2. The horizontal thrust of the cylinder 5 acts on the side of the empty pallet 2 through the push plate 334, pushing the empty pallet 2 to move along the roller assembly 333. At this time, there is rolling friction between the empty pallet 2 and the roller assembly 333. Compared with the sliding friction between the empty pallet 2 and the surface of the machine body 1, the running resistance is greatly reduced. This effectively reduces scratches and wear on the bottom surface of the empty pallet 2, extends the service life of the empty pallet 2, and also significantly reduces the pushing load of the cylinder 5, avoiding problems such as pushing jamming and the empty pallet 2 deviating from its course, ensuring that the empty pallet 2 can be accurately delivered to the docking station of the downstream automated production line. During this process, the PLC controller monitors the extension stroke of the cylinder 5 in real time through the delivery position sensor matched with the cylinder 5. When the empty pallet 2 is completely discharged, the controller immediately controls the cylinder 5 to stop extending, thus completing the delivery of the entire empty pallet 2.

[0046] When the PLC controller confirms that the empty pallet 2 has been conveyed and discharged, it immediately outputs a control command to control the output shaft of cylinder 5 to retract. During the retraction of cylinder 5, wedge block 344 moves synchronously with control plate 322. The wedge engagement between wedge block 344 and wedge plate 342 is gradually released, and the vertical lifting force on wedge plate 342 is completely eliminated. Under the action of their own gravity, roller assembly 333, mounting plate 332, slide rod 335, and wedge plate 342 fall back to reset along the guide of slide rod 335. Roller assembly 333 retracts back into the machine body 1, returning to the initial low position below the upper surface of machine body 1, making way for the natural fall of subsequent stacked empty pallets 2. At the same time, push plate 334 retracts synchronously with the output shaft of cylinder 5, completely avoiding the stacking station of empty pallets 2. This reset process is synchronized with the reset action of the preceding lifting component 31. After the cylinder 5 is fully retracted, the lifting component 31, the conveying component 33, and the associated component 34 all return to their initial standby posture. After the PLC controller receives the signal from the reset position sensor, the machine body 1 enters the standby state, waiting for the next production line feeding instruction.

[0047] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A PLC-controlled dual-limit pallet lifting conveyor, characterized in that: include, Body (1) for carrying empty pallets (2); Cylinder (5) and gantry (4) are fixedly installed on the machine body (1); The feeding mechanism (3) is disposed between the machine body (1) and the gantry (4), and the feeding mechanism (3) includes, The lifting assembly (31) and the control assembly (32) connected to the output end of the cylinder (5) are used to control the lifting assembly (31) to first extend under the second to last empty tray (2) and then lift the second to last and above empty trays (2). The conveying component (33) and the associated component (34) move with the control component (32) and, after the second to last empty pallet (2) is lifted, roll up and push the lowest empty pallet (2).

2. The PLC-controlled dual-limit pallet lifting conveyor as described in claim 1, characterized in that: The lifting assembly (31) includes several fixed plates (311) fixedly installed on the gantry (4). Guide rods (312) are fixedly installed between the fixed plates (311) and the gantry (4). A lifting frame (313) is slidably installed on the outer side of the several guide rods (312).

3. The PLC-controlled dual-limit pallet lifting conveyor as described in claim 2, characterized in that: A mounting frame (314) is fixedly installed on the lifting frame (313), and a plurality of reset springs (315) are fixedly installed on the mounting frame (314). A reset plate (316) is installed at the end of the plurality of reset springs (315).

4. The PLC-controlled dual-limit pallet lifting conveyor as described in claim 3, characterized in that: The reset plate (316) is fixedly installed with a limiting rod (318) of a sliding through mounting bracket (314), and a lifting plate (317) is fixedly installed at the end of the limiting rod (318).

5. The PLC-controlled dual-limit pallet lifting conveyor as described in claim 4, characterized in that: The control assembly (32) includes a control frame (321) fixedly installed on the outside of the output shaft of the cylinder (5), a plurality of control plates (322) are fixedly installed on the control frame (321), and a wedge-shaped frame (323) that cooperates with the corresponding control plate (322) is fixedly installed on the reset plate (316).

6. The PLC-controlled dual-limit pallet lifting conveyor as described in claim 5, characterized in that: The control plate (322) is provided with a protrusion, and the reset plate (316) is provided with an inclined surface (324) that cooperates with the wedge shape of the protrusion.

7. The PLC-controlled dual-limit pallet lifting conveyor as described in claim 6, characterized in that: The conveying assembly (33) includes a support plate (331) fixedly installed on the inner wall of the machine body (1). An installation plate (332) is slidably installed on the support plate (331) via several slide rods (335). A roller assembly (333) is fixedly installed on the installation plate (332). Several openings corresponding to the roller assembly (333) are provided on the upper surface of the machine body (1).

8. The PLC-controlled dual-limit pallet lifting conveyor as described in claim 7, characterized in that: A push plate (334) is fixedly installed at the output end of the cylinder (5), and the push plate (334) is used to push the empty tray (2).

9. The PLC-controlled dual-limit pallet lifting conveyor as described in claim 8, characterized in that: The associated component (34) includes several slides (341) formed on the body (1), and wedge blocks (344) are fixedly installed on the control plate (322) through a connecting frame (343). Several wedge blocks (344) are connected to each other through a connecting plate (345).

10. The PLC-controlled dual-limit pallet lifting conveyor as described in claim 9, characterized in that: The corresponding slide bar (335) is equipped with a wedge plate (342) at its end, and the wedge block (344) is wedge-shapedly engaged with the corresponding wedge plate (342).

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