A flat paper offset automatic waste stripping system and method with a bidirectional toothed paper clamping mechanism

Abstract

The application discloses a kind of flat paper offset automatic rejection system and method with two-way toothed paper mechanism, belong to flat paper printing mechanical equipment technical field, to solve the problem that existing flat paper offset press cannot automatically remove waste after online detection.The system includes two-way toothed trajectory toothed block arranged along the movement direction of toothed paper row, and the control unit controls the two-way toothed trajectory toothed block to avoid the toothed paper row clamping waste at the upstream toothed trajectory according to the waste detection signal, so that the waste lags behind to release at the downstream toothed trajectory;The paper guide structure guides the waste into the negative pressure suction belt, the positive pressure air blowing device assists the paper to adhere, the movable belt vacuum cavity generates negative pressure adsorption force to transport the waste, and the waste falls into the receiving box through the discharging guide.The application can automatically remove defective products during high-speed continuous operation of the printing machine, without stopping, and can be installed in situ above the finished product discharging tray.

Description

Technical Field

[0001] This invention relates to the field of sheet-fed printing machinery and equipment, specifically to an automatic waste rejection system and method for sheet-fed offset printing with a bidirectional toothed paper-gripping mechanism. Background Technology

[0002] Sheet-fed offset printing presses are widely used in the printing and packaging industries, including food, books, cosmetics, cigarette packaging, and electronic packaging. Sheet-fed offset printing presses are large-scale continuous production lines; once started, they operate at high speeds without stopping except during production changes or special circumstances, typically reaching speeds of up to 15,000 sheets per hour. To ensure print quality, machine vision online inspection systems are widely deployed in sheet-fed offset printing presses. These systems capture real-time image information of the sheet paper surface during the printing process and detect printing defects or inherent flaws in the raw paper.

[0003] However, despite the ability of machine vision systems to identify defects in real time, the current paper receiving and sorting structures of sheet-fed offset printing presses still have the following technical shortcomings in actual operation: First, there is a disconnect between online inspection and physical rejection, allowing defective products to be directly mixed into the finished product. Existing sheet-fed offset printing presses typically only have a single fixed gripper block above the finished product tray. All printed sheets are uniformly gripped and conveyed to the finished product tray by a gripper bar driven by a circulating chain, and are forcibly released when passing the fixed gripper block. Because the machine lacks a selective sorting mechanism linked to the visual inspection results, detected waste paper still falls into the finished product tray at the fixed gripper block and mixes with qualified products. This prevents subsequent processes from blocking the flow of defective products, hindering the full utilization of the visual inspection system.

[0004] Secondly, under ultra-high-speed operation, the diversion and stable reception of waste paper is extremely difficult. At ultra-high speeds of up to 15,000 sheets per hour, the paper transfer window is extremely short; if the waste paper is released with a delay, it is easily disturbed by the high-speed turbulent airflow the moment it leaves the gripper bar, causing it to drift, fold, slip, or wrinkle, making it difficult to transition stably to the waste collection end.

[0005] Third, the limited space in the paper receiving area makes conventional negative pressure conveying structures poorly adaptable. The finished paper receiving end of sheet-fed offset printing presses has a compact structure, and existing conventional negative pressure conveying structures mostly adopt a multi-cavity series configuration. This not only results in large vacuum leakage and slow vacuum build-up, but also makes it difficult to flexibly adjust the position and feed angle according to different printed product widths, failing to meet the requirements of in-situ installation and reliable adsorption conveying.

[0006] Therefore, how to provide an automatic waste rejection system that can directly dock in situ, achieve selective opening of the gripper bar at two positions, and has a stable pneumatic transition adsorption capability without affecting the ultra-high-speed continuous printing of sheet-fed offset printing presses is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide an automatic waste rejection system and method for sheet-fed offset printing with a bidirectional paper-gripping mechanism, in order to solve the technical problems in existing sheet-fed offset printing presses, such as the disconnect between online detection and physical waste rejection, the difficulty in smoothly diverting and receiving waste paper under ultra-high-speed conditions, and the difficulty in installing conventional negative pressure conveying structures in place and adapting them to different paper sizes due to limited space in the paper collection area. This invention enables the automatic rejection of defective products during high-speed continuous printing without affecting the normal continuous operation of the printing press.

[0008] The first aspect of this invention provides an automatic waste rejection system for sheet-fed offset printing with a bidirectional gripper mechanism, comprising a gripper bar that moves along a preset trajectory, characterized in that the waste rejection system includes: A bidirectional paper-gripping mechanism includes a cylinder motion control structure and a bidirectional paper-gripping block. The bidirectional paper-gripping block has an upstream paper-gripping trajectory and a downstream paper-gripping trajectory along the movement direction of the paper-gripping gripper bar. The cylinder motion control structure drives the bidirectional paper-gripping block to switch between a normal paper-gripping position and an avoidance position. In the normal paper-gripping position, the bidirectional paper-gripping block engages with the paper-gripping gripper bar at the upstream paper-gripping trajectory to open the paper-gripping gripper bar. In the avoidance position, the bidirectional paper-gripping block avoids the paper-gripping gripper bar at the upstream paper-gripping trajectory to keep the paper-gripping gripper bar closed. The downstream paper-gripping trajectory is located downstream of the movement direction of the paper-gripping gripper bar, and the bidirectional paper-gripping block engages with the paper-gripping gripper bar at the downstream paper-gripping trajectory to open the paper-gripping gripper bar. A belt frame, on which belt guide pulleys are provided; A negative pressure suction belt is wound around the belt guide pulley to form a conveying surface, and the feed end of the negative pressure suction belt is connected to the paper guiding structure. A movable belt vacuum chamber is located inside the negative pressure suction belt, the negative pressure suction belt covers the movable belt vacuum chamber, and the movable belt vacuum chamber is configured to generate negative pressure adsorption force on the conveying surface of the negative pressure suction belt. The paper guiding structure is directly connected to the sheet metal frame inside the maintenance window above the finished product unloading tray of the sheet offset printing machine, and is located below the movement trajectory of the gripper bar, between the bidirectional gripper track gripper block and the movable belt vacuum chamber. The positive pressure air blowing device is positioned towards the feed end of the negative pressure suction belt; A waste discharge guide and receiving box are located at the discharge end of the negative pressure suction belt; and The control unit is communicatively connected to the cylinder motion control structure and is used to receive the scrap detection signal from the online visual inspection system, and control the cylinder motion control structure to drive the bidirectional tooth-opening trajectory tooth-opening block to switch from the normal tooth-opening position to the avoidance position according to the scrap detection signal.

[0009] Furthermore, during normal operation of the waste rejection system, the bidirectional toothing track toothing block remains in the normal toothing position at the upstream toothing track; when the control unit receives the waste detection signal, the control unit controls the cylinder motion control structure to drive the bidirectional toothing track toothing block, causing its upstream toothing track to switch to an avoidance position, so that the paper gripper holding the waste remains closed and continues to move to the downstream toothing track of the bidirectional toothing track toothing block.

[0010] Furthermore, the apex of the downstream opening trajectory of the bidirectional opening trajectory opening block corresponds to the feed end of the negative pressure suction belt.

[0011] Furthermore, the paper guiding structure is an arc-shaped guide sheet metal part, configured to guide the paper into the feed end of the negative pressure suction belt in an arc-shaped path.

[0012] Furthermore, the belt guide pulley is a split-type belt guide pulley, which is independently installed on the belt frame, and the position of the split-type belt guide pulley can be adjusted individually.

[0013] Furthermore, the split-type belt guide pulley is configured to adjust the inlet angle of the negative pressure suction belt by adjusting its position, and to control the gap between the negative pressure suction belt and the movable belt vacuum chamber.

[0014] Furthermore, the movable belt vacuum chamber is connected to the belt frame via a guide shaft. The movable belt vacuum chamber is configured to adjust its position within the defined range of the belt frame along the guide shaft to accommodate printing products of different sizes. The movable belt vacuum chamber is equipped with an independent vacuum source.

[0015] Furthermore, the negative pressure suction belt is embedded in the guide groove of the movable belt vacuum cavity, and the negative pressure suction belt has an adsorption hole with a diameter of 6mm. The negative pressure suction belt is made of polyurethane material with surface roughening treatment.

[0016] Furthermore, it also includes an adjustable belt pressure roller, which is mounted above the belt frame via a gantry bracket.

[0017] Furthermore, the installation position of the adjustable belt pressure roller is configured to adapt to the position of the negative pressure suction belt, and the adjustable belt pressure roller is configured to apply pre-tightening pressure to the paper adsorbed on the negative pressure suction belt.

[0018] Furthermore, the waste discharge guide and receiving box includes an inclined guide groove and a receiving box body. The inclined guide groove is located below the discharge end of the negative pressure suction belt, and the receiving box body is located at the end of the inclined guide groove.

[0019] Furthermore, the positive pressure air blowing device blows air toward the position where the feed end of the negative pressure suction belt is tangent to the belt guide pulley.

[0020] A second aspect of the present invention provides an automatic rejection method for sheet-fed offset printing, comprising the following steps: S1: After the online visual inspection system identifies waste, it transmits the waste detection signal to the control unit. The control unit records the position information of the paper gripper bar where the waste is located and tracks the movement of the paper gripper bar. S2: When the paper gripper carrying the waste runs to the position of the upstream opening track of the bidirectional opening track opening block, the control unit controls the cylinder motion control structure to drive the bidirectional opening track opening block, so that its upstream opening track moves to the avoidance position, and the paper gripper remains closed and continues to move; S3: The waste enters the paper guiding structure. When the paper gripper bar runs to the downstream position of the bidirectional opening track opening block, the bidirectional opening track opening block opens the paper gripper bar at its downstream opening track, and the waste is released. S4: The positive pressure blowing device blows air onto the waste, causing the waste to adhere to the conveying surface of the negative pressure suction belt. The movable belt vacuum chamber generates negative pressure adsorption force to adsorb the waste onto the negative pressure suction belt and convey it. S5: After the waste material leaves the negative pressure area of ​​the movable belt vacuum chamber, it continues to move by relying on the friction of the negative pressure suction belt and the thrust of the waste material that has not yet left the chamber. It then falls into the receiving box through the waste material discharge guide.

[0021] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes a bidirectional opening block with upstream and downstream opening trajectories along the movement path of the gripper bar. The control unit, based on waste detection signals from an online visual inspection system, controls the bidirectional opening block to avoid the gripper bar holding waste at the upstream opening trajectory. This prevents the waste gripper bar from opening above the finished product tray, instead continuing its movement to the downstream opening trajectory for delayed opening and release, thus separating waste from qualified products. The entire waste removal process requires no machine downtime and does not affect the normal continuous operation of the sheet-fed offset printing press.

[0022] This invention achieves a smooth transition through the coordinated operation of a paper guiding structure, a positive pressure air blowing device, a negative pressure suction belt, and an adjustable belt roller: After being guided along an arc-shaped path, waste paper is blown by the positive pressure air blowing device towards the tangential position of the belt guide roller, assisting the paper in adhering to the surface of the negative pressure suction belt; the movable belt vacuum chamber generates negative pressure adsorption force to attract the paper onto the belt for transport; the adjustable belt roller applies pre-tension pressure to the paper, guiding its movement and preventing vacuum leakage due to insufficient paper flatness, which could cause the paper to detach from the belt. Adsorption holes on the negative pressure suction belt prevent wrinkling and denting deformation during paper adsorption, and the surface-roughened polyurethane material increases the coefficient of friction, preventing slippage during operation.

[0023] This invention directly connects to the operating door above the finished product unloading tray of a sheet-fed offset printing machine, eliminating the need for modifications to the main body of the printing press. The split-type belt guide pulley is independently mounted on the belt frame and its position can be individually adjusted to change the belt inlet angle, adapting to various feeding conditions. It also precisely controls the gap between the belt and the vacuum chamber, suppressing vacuum leakage and reducing belt friction. The movable belt vacuum chamber is connected to the belt frame via a guide shaft, allowing its position to be adjusted within the belt frame's defined range, accommodating printed products of different sizes. Furthermore, each chamber has an independent vacuum source, effectively avoiding the problems of large vacuum leakage and low vacuum build-up rate associated with multi-chamber series structures.

[0024] After the waste paper is removed from the negative pressure area of ​​the vacuum chamber by the negative pressure suction belt, it relies on its own inertia and the friction driven by the belt to detach from the belt line and slide down the inclined guide groove into the independent waste receiving box. Normal paper is still collected by the finished product discharge tray. The two collection paths do not interfere with each other. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments; Figure 1 This is a schematic diagram of the overall structure of the automatic waste rejection system for sheet-fed offset printing with a bidirectional toothed paper-grabbing mechanism provided in an embodiment of the present invention. Figure 2 This is a partial structural schematic diagram of the bidirectional toothed paper-grabbing mechanism provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the overall layout of the waste rejection system installed on a sheet-fed offset printing press according to an embodiment of the present invention. Figure 4 This is a side view of the waste removal system provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the overall structure of the waste removal system provided in an embodiment of the present invention from another perspective.

[0026] In the diagram: 1. Paper guiding structure; 2. Feed positive pressure blowing device; 3. Split belt guide pulley; 4. Movable belt vacuum chamber; 5. Adjustable belt pressure pulley; 6. Negative pressure suction belt. Detailed Implementation

[0027] This section will describe in detail specific embodiments of the present invention. Preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and overall technical solution of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0028] Example 1 like Figure 1 As shown and referenced Figures 2 to 5 This invention provides an automatic waste rejection system for sheet-fed offset printing with a bidirectional gripper mechanism, comprising a gripper bar that moves along a preset trajectory, the waste rejection system comprising: like Figure 2 As shown, the bidirectional paper-gripping mechanism includes a cylinder motion control structure and a bidirectional paper-gripping track block. The bidirectional paper-gripping track block is a redesigned version of the original paper-gripping block, transforming it into a cylinder-controlled paper-gripping structure. The bidirectional paper-gripping track block has an upstream paper-gripping track and a downstream paper-gripping track along the movement direction of the paper-gripping tooth bar, and is driven by a cylinder to switch between a normal paper-gripping position and a avoidance position. In the normal paper-gripping position, the bidirectional paper-gripping track block engages with the paper-gripping tooth bar at the upstream paper-gripping track to open the paper-gripping tooth bar. In the avoidance position, the bidirectional paper-gripping track block avoids the paper-gripping tooth bar at the upstream paper-gripping track to keep the paper-gripping tooth bar closed. The downstream paper-gripping track is located at the junction of the bidirectional paper-gripping track block and the movable belt vacuum chamber 4. The bidirectional paper-gripping track block engages with the paper-gripping tooth bar at the downstream paper-gripping track to open the paper-gripping tooth bar. The paper guide structure 1 is directly connected to the sheet metal frame inside the maintenance window above the finished product feeding tray of the sheet offset printing machine, and is located below the movement trajectory of the gripper bar, between the bidirectional gripper track gripper block and the movable belt vacuum chamber 4. A belt frame, on which belt guide pulleys 3 are provided; A negative pressure suction belt 6 is wound around the belt guide pulley 3 to form a conveying surface, and the feed end of the negative pressure suction belt 6 is connected to the paper guide structure 1. The movable belt vacuum chamber 4 is a hollow cavity structure, located inside the negative pressure suction belt 6. The negative pressure suction belt 6 covers the movable belt vacuum chamber 4, and the movable belt vacuum chamber 4 is configured to generate negative pressure adsorption force on the conveying surface of the negative pressure suction belt 6. The positive pressure air blowing device 2 is positioned towards the feed end of the negative pressure suction belt 6; A waste discharge guide and receiving box are located at the discharge end of the negative pressure suction belt 6; and The control unit is communicatively connected to the cylinder and is used to receive the scrap detection signal from the online visual inspection system, and control the cylinder to drive the bidirectional tooth-opening trajectory tooth-opening block to switch from the normal tooth-opening position to the avoidance position according to the scrap detection signal.

[0029] As one implementation method, the online visual inspection system described in this embodiment includes an upper inspection camera and a lower inspection camera, which are used to collect image information of the upper and lower surfaces of the flat paper to detect printing defects and defects inherent in the raw paper.

[0030] In one implementation, when the waste rejection system in this embodiment is operating normally, the bidirectional opening trajectory opening block is maintained at the normal opening position at the upstream opening trajectory; when the control unit receives the waste detection signal, the control unit controls the cylinder to drive the bidirectional opening trajectory opening block, so that its upstream opening trajectory switches to the avoidance position, so that the paper gripper bar holding the waste remains closed and continues to move to the downstream opening trajectory of the bidirectional opening trajectory opening block.

[0031] In one implementation, the apex of the downstream opening trajectory of the bidirectional opening trajectory opening block in this embodiment corresponds to the feed end of the negative pressure suction belt 6. When the paper gripper passes through the downstream opening trajectory, the opening is released, allowing the paper to dock with the negative pressure suction belt 6.

[0032] In one embodiment, the paper guiding structure 1 described in this example is an arc-shaped guide sheet metal part, configured to guide the paper into the feed end of the negative pressure suction belt 6 in an arc-shaped path.

[0033] In one embodiment, the belt guide pulley 3 is a split belt guide pulley, which is independently installed on the belt frame, and the position of the split belt guide pulley can be adjusted individually.

[0034] As one implementation method, the split belt guide wheel in this embodiment is configured to adjust the inlet angle of the negative pressure suction belt 6 by adjusting its position, so as to adapt to various feeding conditions and control the gap between the negative pressure suction belt 6 and the movable belt vacuum chamber 4, effectively suppressing vacuum leakage problems and alleviating belt friction.

[0035] In one embodiment, the movable belt vacuum chamber 4 is connected to the belt frame via a guide shaft. The movable belt vacuum chamber 4 is configured to adjust its position within the defined range of the belt frame along the guide shaft to accommodate printing products of different sizes. The movable belt vacuum chamber 4 is equipped with an independent vacuum source, which can effectively avoid the problems of large vacuum leakage and low vacuum build-up rate caused by the multi-chamber series structure.

[0036] In one embodiment, the negative pressure suction belt 6 is embedded in the guide groove of the movable belt vacuum chamber 4 to enhance the negative pressure adsorption force; the negative pressure suction belt 6 has adsorption holes with a diameter of 6mm, the size of which is adapted to the paper to be adsorbed, which can effectively prevent wrinkling and denting deformation of the paper during adsorption; the negative pressure suction belt 6 is made of polyurethane material with surface roughening treatment, which can improve the friction coefficient and prevent slippage during operation.

[0037] As one implementation, this embodiment also includes an adjustable belt pressure roller 5, which is mounted above the belt frame via a gantry bracket.

[0038] As one implementation method, the installation position of the adjustable belt pressure roller 5 in this embodiment is configured to adapt to the position of the negative pressure suction belt 6, which has strong adaptability; the adjustable belt pressure roller 5 is configured to apply pre-tightening pressure to the paper adsorbed on the negative pressure suction belt 6, which on the one hand guides the movement of the paper, and on the other hand avoids vacuum leakage caused by insufficient flatness of paper adsorption, thereby preventing the paper from falling off the belt surface.

[0039] In one embodiment, the waste discharge guide and receiving box in this embodiment includes an inclined guide groove and a receiving box body. The inclined guide groove is located below the discharge end of the negative pressure suction belt 6, and the receiving box body is located at the end of the inclined guide groove.

[0040] In one embodiment, the positive pressure air blowing device 2 blows air toward the position where the feed end of the negative pressure suction belt 6 is tangent to the belt guide wheel 3, so as to help the paper adhere to the negative pressure suction belt 6.

[0041] like Figure 3As shown, the waste rejection system in this embodiment is installed above the finished product feeding tray of the sheet offset printing machine. The upper and lower detection cameras of the online vision inspection system collect images from the upper and lower surfaces of the sheet paper, respectively. The gripper bar clamps and conveys the paper along the circulation path. The bidirectional gripper mechanism is set along the movement direction of the gripper bar. Normal paper is collected at the finished product feeding tray. The detected waste is guided by the paper guide structure 1 and collected by the waste discharge guide and the receiving box, forming two non-interfering receiving paths for finished products and waste.

[0042] like Figure 4 As shown in the side view, the bidirectional opening track of the bidirectional paper-gripping mechanism has two opening positions: an upstream opening track and a downstream opening track. It switches between the normal opening position and the avoidance position. The positive pressure blowing device 2 blows positive pressure air towards the feed end of the negative pressure suction belt 6. The adjustable belt pressure roller 5 presses against the negative pressure suction belt 6. After being released, the paper is adhered to the negative pressure suction belt 6 through the paper guide structure 1 and is discharged from it, realizing the smooth diversion and transition of waste paper.

[0043] Figure 5 This is a schematic diagram of the overall structure of the waste removal system from another perspective in this embodiment, showing the composition and connection relationship of its components. Figure 1 Consistent.

[0044] The working process of this embodiment is as follows: The upper and lower detection cameras of the online visual inspection system respectively acquire image information of the upper and lower surfaces of the sheet paper. After identifying defective waste products, the waste product detection signal is transmitted to the control unit. The control unit records the position information of the gripper bar where the waste product is located and tracks the movement of the gripper bar. When the gripper bar carrying the waste product moves to the upstream gripper track position of the bidirectional gripper track above the finished product feeding tray, the control unit controls the cylinder to drive the bidirectional gripper track to switch to the avoidance position, so that it does not open at the upstream gripper track, and the gripper bar carrying the waste product remains closed and continues to run. The front end of the waste product enters the paper guide structure 1 first, and then the gripper bar moves to the downstream gripper track position of the bidirectional gripper track, and the gripper bar opens. Under the blowing action of the positive pressure blowing device 2, the waste paper adheres to the surface of the negative pressure suction belt 6. Then, the negative pressure adsorption force generated by the movable belt vacuum chamber 4 drives the waste paper to move with the negative pressure suction belt 6. The adjustable belt pressure roller 5 applies pre-tight pressure to the waste paper to prevent it from falling off during the conveying process. When the waste paper moves out of the negative pressure area of ​​the movable belt vacuum chamber 4, the negative pressure disappears, and the waste paper relies on its own inertia and the friction force driven by the negative pressure suction belt 6 to detach from the belt and slide down the inclined guide groove into the receiving box, completing the waste removal. This process does not affect the continuous operation of the printing press, and waste separation can be achieved without stopping the machine. Normal paper is still collected by the finished product discharge tray.

[0045] Example 2 This embodiment provides an automatic rejection method for sheet-fed offset printing, including the following steps: S1: The online visual inspection system collects image information of the upper and lower surfaces of the flat paper through the upper and lower inspection cameras. After identifying the waste, it transmits the waste detection signal to the control unit. The control unit records the position information of the gripper bar where the waste is located and tracks the movement of the gripper bar. S2: When the paper gripper carrying the waste moves to the position of the upstream opening track of the bidirectional opening track opening block, the control unit controls the bidirectional opening track opening block to move its upstream opening track to the avoidance position, and the paper gripper remains closed and continues to move; S3: The waste enters the paper guide structure 1. When the paper gripper bar runs to the position of the downstream opening track of the bidirectional opening track opening block, the opening point of the downstream opening track causes the paper gripper bar to open and the waste is released. S4: The positive pressure air blowing device 2 blows air onto the waste, causing the waste to adhere to the conveying surface of the negative pressure suction belt 6. The movable belt vacuum chamber 4 generates negative pressure adsorption force to adsorb the waste onto the negative pressure suction belt 6 and convey it. S5: After the waste material leaves the negative pressure area of ​​the movable belt vacuum chamber 4, it continues to move by relying on the friction of the negative pressure suction belt 6 and the thrust of the waste material that has not yet left the vacuum chamber. It then falls into the receiving box through the waste material discharge guide.

[0046] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. An automatic waste rejection system for sheet-fed offset printing with a bidirectional paper-gripping mechanism, comprising a paper-gripping gripper bar that moves along a preset trajectory, characterized in that, The rejection system includes: A bidirectional paper-gripping mechanism includes a cylinder motion control structure and a bidirectional paper-gripping block. The bidirectional paper-gripping block has an upstream paper-gripping trajectory and a downstream paper-gripping trajectory along the movement direction of the paper-gripping gripper bar. The cylinder motion control structure drives the bidirectional paper-gripping block to switch between a normal paper-gripping position and an avoidance position. In the normal paper-gripping position, the bidirectional paper-gripping block engages with the paper-gripping gripper bar at the upstream paper-gripping trajectory to open the paper-gripping gripper bar. In the avoidance position, the bidirectional paper-gripping block avoids the paper-gripping gripper bar at the upstream paper-gripping trajectory to keep the paper-gripping gripper bar closed. The downstream paper-gripping trajectory is located downstream of the movement direction of the paper-gripping gripper bar, and the bidirectional paper-gripping block engages with the paper-gripping gripper bar at the downstream paper-gripping trajectory to open the paper-gripping gripper bar. A belt frame, on which belt guide pulleys are provided; A negative pressure suction belt is wound around the belt guide pulley to form a conveying surface, and the feed end of the negative pressure suction belt is connected to the paper guiding structure. A movable belt vacuum chamber is located inside the negative pressure suction belt, the negative pressure suction belt covers the movable belt vacuum chamber, and the movable belt vacuum chamber is configured to generate negative pressure adsorption force on the conveying surface of the negative pressure suction belt. The paper guiding structure is directly connected to the sheet metal frame inside the maintenance window above the finished product unloading tray of the sheet offset printing machine, and is located below the movement trajectory of the gripper bar, between the bidirectional gripper track gripper block and the movable belt vacuum chamber. The positive pressure air blowing device is positioned towards the feed end of the negative pressure suction belt; A waste discharge guide and receiving box are located at the discharge end of the negative pressure suction belt; and The control unit is communicatively connected to the cylinder motion control structure and is used to receive the scrap detection signal from the online visual inspection system, and control the cylinder motion control structure to drive the bidirectional tooth-opening trajectory tooth-opening block to switch from the normal tooth-opening position to the avoidance position according to the scrap detection signal.

2. The automatic waste rejection system for sheet-fed offset printing with a bidirectional paper-gripping mechanism according to claim 1, characterized in that, When the waste rejection system is operating normally, the bidirectional tooth-opening trajectory tooth-opening block is maintained at the normal tooth-opening position at the upstream tooth-opening trajectory. When the control unit receives the waste detection signal, the control unit controls the cylinder motion control structure to drive the bidirectional tooth-opening trajectory tooth-opening block, so that its upstream tooth-opening trajectory switches to the avoidance position, so that the paper gripper holding the waste remains closed and continues to move to the downstream tooth-opening trajectory of the bidirectional tooth-opening trajectory tooth-opening block.

3. The automatic waste rejection system for sheet-fed offset printing with a bidirectional paper-gripping mechanism according to claim 1 or 2, characterized in that, The apex of the downstream opening trajectory of the bidirectional opening trajectory opening block corresponds to the feed end of the negative pressure suction belt.

4. The automatic waste rejection system for sheet-fed offset printing with a bidirectional paper-gripping mechanism according to claim 1, characterized in that, The paper guiding structure is an arc-shaped guide sheet metal part, configured to guide the paper into the feed end of the negative pressure suction belt in an arc-shaped path.

5. The automatic waste rejection system for sheet-fed offset printing with a bidirectional paper-gripping mechanism according to claim 1, characterized in that, The belt guide pulley is a split-type belt guide pulley, which is independently installed on the belt frame, and the position of the split-type belt guide pulley can be adjusted individually.

6. The automatic waste rejection system for sheet-fed offset printing with a bidirectional paper-gripping mechanism according to claim 5, characterized in that, The split-type belt guide pulley is configured to adjust the inlet angle of the negative pressure suction belt and control the gap between the negative pressure suction belt and the movable belt vacuum chamber by adjusting its position.

7. The automatic waste rejection system for sheet-fed offset printing with a bidirectional paper-gripping mechanism according to claim 1, characterized in that, The movable belt vacuum chamber is connected to the belt frame via a guide shaft. The movable belt vacuum chamber is configured to adjust its position within the defined range of the belt frame along the guide shaft to accommodate printing products of different sizes. The movable belt vacuum chamber is equipped with an independent vacuum source.

8. The automatic waste rejection system for sheet-fed offset printing with a bidirectional paper-gripping mechanism according to claim 1, characterized in that, The negative pressure suction belt is embedded in the guide groove of the movable belt vacuum chamber. The negative pressure suction belt has an adsorption hole with a diameter of 6mm. The negative pressure suction belt is made of polyurethane material with surface roughening treatment.

9. The automatic waste rejection system for sheet-fed offset printing with a bidirectional paper-gripping mechanism according to claim 1, characterized in that, It also includes an adjustable belt pressure roller, which is mounted above the belt frame via a gantry bracket; the installation position of the adjustable belt pressure roller is configured to adapt to the position of the negative pressure suction belt, and the adjustable belt pressure roller is configured to apply pre-tightening pressure to the paper adsorbed on the negative pressure suction belt.

10. An automatic waste rejection method for sheet-fed offset printing, characterized in that, The method employs the system as described in any one of claims 1 to 9, and includes the following steps: S1: After the online visual inspection system identifies waste, it transmits the waste detection signal to the control unit. The control unit records the position information of the paper gripper bar where the waste is located and tracks the movement of the paper gripper bar. S2: When the paper gripper carrying the waste runs to the position of the upstream opening track of the bidirectional opening track opening block, the control unit controls the cylinder motion control structure to drive the bidirectional opening track opening block, so that its upstream opening track moves to the avoidance position, and the paper gripper remains closed and continues to move; S3: The waste enters the paper guiding structure. When the paper gripper bar runs to the downstream position of the bidirectional opening track opening block, the bidirectional opening track opening block opens the paper gripper bar at its downstream opening track, and the waste is released. S4: The positive pressure blowing device blows air onto the waste, causing the waste to adhere to the conveying surface of the negative pressure suction belt. The movable belt vacuum chamber generates negative pressure adsorption force to adsorb the waste onto the negative pressure suction belt and convey it. S5: After the waste material leaves the negative pressure area of ​​the movable belt vacuum chamber, it continues to move by relying on the friction of the negative pressure suction belt and the thrust of the waste material that has not yet left the chamber. It then falls into the receiving box through the waste material discharge guide.

Images