Cam connecting rod mechanism for negative pressure type fresh food packaging machine

Abstract

The invention discloses a cam connecting rod mechanism for a negative pressure type fresh food packaging machine. The cam connecting rod mechanism comprises a crank, a connecting rod, a connecting frame rod, a sliding block, a variable-length rack and a cam. According to the cam connecting rod mechanism for the negative pressure type fresh food packaging machine, a specified point on a connecting rod plane can move according to a given track. The linear part of the track is used for heat sealing operation, so that the heat sealing head and the packaging film can move synchronously, and the situation that the film is scraped by a cutter due to the fact that the moving speed of the heat sealing head and the moving speed of the packaging film are not matched is avoided while enough heat sealing time is guaranteed. In addition, the curve part of the track is used for avoiding the materials, that is, after heat sealing is finished, the heat sealing head can be rapidly lifted to cross the packaging box and retreat.

Description

Technical Field

[0001] The present invention relates to the field of machinery, and in particular to a cam connecting rod mechanism for a negative pressure fresh food packaging machine. Background Art

[0002] Fresh foods such as fruits, vegetables, aquatic products, and meats have high moisture content, short shelf life, and are easily damaged by external forces during transportation. Therefore, appropriate packaging is required to reduce losses during sales. In the packaging of fresh foods, the most commonly used packaging method by processing companies and supermarkets is to place the fresh food in the packaging box first, and then wrap it with a layer of packaging film (such as polyvinyl chloride film) to achieve packaging. This packaging method is low-cost, can effectively reduce the loss of fresh food, and has a beautiful appearance. When this packaging method is used, the packaging film is placed on the film feeding mechanism, and the packaging film is transported to the rear of the frame by the traction of the film feeding mechanism roller. The packaging box containing the material is put into the conveyor belt of the conveying device. At this time, the packaging film is above the packaging box, and the packaging film and the packaging box move synchronously to the next station. When the packaging film passes through the longitudinal sealing device, the longitudinal sealing device tightens the packaging film, and the packaging film is gathered into a cylindrical shape to complete the bag forming of the packaging film. At this time, the packaging box is wrapped in the cylindrical packaging film. The conveying device continues to transport forward, and the horizontal sealing and cutting mechanism completes the heat sealing and cutting of the packaging film between the front and rear packaging boxes. The packaging box that has completed longitudinal and transverse sealing is sucked together by the negative pressure suction device to make the packaging film fit tightly to the packaging box. During the working process, the transverse sealing and cutting mechanism needs to move synchronously with the packaging film during the heat sealing operation, and needs to avoid the packaging box and return it after the heat sealing operation. Therefore, the working efficiency of the transverse sealing and cutting mechanism determines the working efficiency of the entire packaging machine.

[0003] like Figure 1 The figure shows the operation diagram of heat sealing and cutting in film packaging. Figure 1 In the figure, 1 is a packaging box, 2 is a heat sealing head of a transverse sealing and cutting mechanism, and 3 is a conveyor belt. When the packaging machine adopts a continuous operation mode, the motion trajectory of the heat sealing head of the transverse sealing and cutting mechanism needs to meet the requirements. Figure 1 The motion trajectory requirements are shown in the dotted line. That is, during the horizontal sealing and cutting operation, the heat sealing head should be able to move synchronously with the packaging film along the linear motion trajectory to achieve heat sealing, and ensure sufficient heat sealing time. After the heat sealing operation is completed, slowly separate to avoid film tearing due to excessive separation speed. Finally, the heat sealing head should be able to quickly lift over the packaged items and return. When the above motion trajectory is adopted, the problems of the cutter scraping the film and the incision being incorrect in the existing horizontal sealing and cutting mechanism can be effectively avoided. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a cam-connecting rod mechanism for a negative pressure fresh food packaging machine that can realize a specified motion trajectory. In order to solve the above technical problem, the technical solution provided by the present invention is as follows:

[0005] A cam-connecting rod mechanism for a negative pressure fresh food packaging machine comprises a crank, a connecting rod, a connecting rod, a fixed slide rail, a cam push rod, a cam, and a frame. The cam is fixedly connected to the crank to push the cam push rod to move back and forth along the frame. Assume that the length of the crank is a, the length of the connecting rod is b, the length of the connecting rod is c, the length of the frame is d, the distance from point E on the connecting rod plane to hinge B is e, the length of the cam push rod is l, and the angle between the line from hinge B to point E and the direction of the connecting rod is θ E , the installation angle of the rack is θ D , the crank angle is θ A , the coordinate of the fixed hinge A of the crank is x A ,y A , the coordinates of the precision control points on the target trajectory are Then the Cartesian coordinates of point E on the connecting rod plane can be expressed as, x E =x A +a·cos(θ A +θ D )+e·cos(θ B +θ E +θ D ) y E =y A +a·sin(θ A +θ D )+e·sin(θ B +θ E +θ D ) in, It is characterized by the lengths of the cam-link mechanism a, b, c, d, the distance e from point E to hinge B, and the direction angle θ E , the coordinate x of the fixed hinge A A ,y A , installation angle θ D , crank angle θ A , should satisfy the equation is the objective function, equation is the constrained optimization equation, and the cam profile should satisfy the equation, R(θ A )=d(θ A )-l, in the constraint equation [γ0] is the allowable transmission angle.

[0006] Preferably, in the cam-connecting rod mechanism, the length of the crank is 39 mm, the length of the connecting rod is 106 mm, the length of the connecting rod is 478 mm, the distance from point E on the connecting rod plane to hinge B is 338 mm, the length of the cam push rod is 450 mm, the angle between the line between points BE and the direction of the connecting rod is 0.01 rad, the installation angle of the frame AD is 0.15 rad, and the x-axis coordinate x of the fixed hinge A is A Equal to 79mm, y-axis coordinate y A Equal to -299mm.

[0007] Preferably, when the cam-link mechanism passes through 20 precision control points, the lengths of the frame are 484.8mm, 486.0mm, 484.6mm, 484.5mm, 485.0mm, 485.3mm, 484.6mm, 484.8mm, 485.0mm, 485.0mm, 485.0mm, 484.8mm, 483.8mm, 484.5mm, 485.8mm, 484.8mm, 484.7mm, 484.6mm, 484.9mm, and 485.6mm respectively.

[0008] The cam connecting rod mechanism for the negative pressure fresh food packaging machine provided by the present invention can make the heat sealing head of the transverse sealing and cutting mechanism move according to the specified trajectory, ensuring the synchronous movement of the heat sealing head and the packaging film and sufficient heat sealing time. At the same time, after the heat sealing operation is completed, it can be slowly separated from the packaging film to avoid film tearing due to too fast separation speed. Finally, the heat sealing head can be quickly lifted over the packaged items and returned. It effectively avoids the problems of the cutter scraping the film and the incision being incorrect in the existing transverse heat sealing mechanism, and can realize continuous transverse heat sealing and cutting operations, avoiding frequent stops of the conveyor belt. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 , Schematic diagram of the operation of transverse heat sealing cutting in film packaging.

[0010] Figure 2 , schematic diagram of the planar four-bar mechanism.

[0011] Figure 3 , schematic diagram of a two-degree-of-freedom five-bar mechanism.

[0012] Figure 4 , schematic diagram of the cam-linkage mechanism.

[0013] Figure 5 , the coordinate system and geometric parameter diagram of the cam-connecting rod mechanism described in the present invention.

[0014] Figure 6 , the target motion trajectory diagram of the heat sealing head when the packaging object is 1912 plastic PP pallet.

[0015] Figure 7 When the packaging object is 1912 plastic PP pallet, the target motion trajectory of the heat sealing head is parallel to the connecting rod.

[0016] Motion trajectory of point E on the surface.

[0017] Figure 8 , the target motion trajectory of the heat sealing head when the packaging object is a 2116 type PET transparent plastic packaging box.

[0018] Fig. 9 , the target motion trajectory of the heat sealing head and the motion trajectory of point E on the connecting rod plane when the packaging object is a 2116 type PET transparent plastic packaging box.

[0019] Fig.10 , applicable to the x-axis and y-axis velocity curves of point E on the connecting rod plane of the cam connecting rod mechanism of 2116 type PET transparent plastic fruit packaging box.

[0020] Fig.11 , applicable to the schematic diagram of the cam-linkage mechanism of 2116 type PET transparent plastic fruit packaging box.

[0021] Fig.12 , 3D model of cam-linkage mechanism for 2116 PET transparent plastic fruit packaging box DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 2 The figure shows a planar four-bar mechanism, the four hinges of which are A, B, C, and D. There is a specified point E on the connecting rod plane of the four-bar mechanism. According to mechanical principles, point E on the connecting rod of the planar four-bar mechanism can generate various forms of motion trajectories, but these trajectories can only accurately fit 5 points. Figure 3 As shown in the figure, when a slider is added to the four-bar mechanism, the planar four-bar mechanism can be transformed into a two-degree-of-freedom five-bar mechanism. However, the two-degree-of-freedom five-bar mechanism requires two independent active parts to meet the uniqueness requirement of the mechanism movement. By adding a cam fixedly connected to the active crank in the two-degree-of-freedom five-bar mechanism, the cam mechanism is used to close the five-bar mechanism with two degrees of freedom, so that it can be transformed into a Figure 4 The four-bar mechanism with variable frame length shown in the figure. The frame length parameter can be obtained from inverse kinematics. By expressing the frame length as a function of the crank angle, a single-degree-of-freedom cam-link mechanism with a precise cam profile is formed.

[0024] Therefore, the present invention proposes Figure 4The cam-link mechanism is used as a prototype mechanism for the control of the transverse heat sealing head of the negative pressure fresh food packaging machine. The cam-link mechanism includes a crank 4, a connecting rod 5, a connecting rod 6, a fixed slide rail 7, a cam push rod 8, a cam 9, and a frame 10. The cam 9 is fixedly connected to the crank 4 to push the cam push rod 8 to move back and forth along the frame 10.

[0025] like Figure 5 As shown, let the length of crank 4 be a, the length of connecting rod 5 be b, the length of connecting rod 6 be c, the length of frame 10 be d, the distance from point E on the plane of connecting rod 5 to hinge B be e, the length of cam push rod 8 be l, and the angle between the line from hinge B to point E and the direction of connecting rod 5 be θ E , the installation angle of the rack 10 is θ D , the rotation angle of crank 4 is θ A , the coordinate of the fixed hinge A of crank 4 is x A ,y A , the coordinates of the precision control points on the target trajectory are From the plane geometry relationship, we know that the Cartesian coordinates of point E on the connecting rod 5 plane can be expressed as: x E =x A +a·cos(θ A +θ D )+e·cos(θ B +θ E +θ D ) y E =y A +a·sin(θ A +θ D )+e·sin(θ B +θ E +θ D ) in, The rod lengths a, b, c, d of the cam-link mechanism, the distance e from point E to hinge B, and the direction angle θ E , the coordinate x of the fixed hinge A A ,y A , installation angle θ D , crank angle θ A , should satisfy the equation is the objective function, equation is the constrained optimization equation, and the radius of each point on the contour line of cam 9 should satisfy the equation, R(θ A )=d(θ A)-l, in the constraint equation [γ0] is the allowable transmission angle.

[0026] To ensure the transmission characteristics of the mechanism, the transmission angle [γ0] should be less than 30 degrees. When the transmission angle [γ0] is greater than 30 degrees, the transmission performance of the cam-link mechanism decreases significantly.

[0027] When the packaging object is a 1912-type plastic PP pallet, the size of the cam linkage mechanism and the contour of the cam 9 can be determined according to the above equation. The length, width and height of the 1912-type plastic PP pallet are 180mm, 120mm and 25mm respectively. According to the requirements of the heat sealing process, the heat sealing process can be divided into three steps, namely heating, heat preservation and pressure maintenance, slow separation and fast retreat. Therefore, the target motion trajectory of the heat sealing head can be determined as follows Figure 6 The target motion trajectory consists of three parts. The first part is the straight line part, which is used to control the heat sealing head to make horizontal uniform linear motion; the second part is the short arc part, which is used to control the heat sealing head to slowly separate from the packaging film; the third part is the long arc curve part, which is used to control the heat sealing head to quickly retreat and pass over the packaged items. In order to achieve the above requirements, 20 precision control points are distributed on the target motion trajectory. The motion trajectory between precision control points 2 to 7 is a horizontal straight line, and the distances between precision control points 2 to 7 are equal, which is used to control the heat sealing head to make horizontal uniform linear motion. The motion trajectory between precision control points 7 to 9 is a short arc line, which controls the heat sealing head to slowly separate from the packaging film to avoid film tearing due to too fast separation speed. The motion trajectory between precision control points 9 to 20 is a long arc curve, which is used for the rapid retreat of the heat sealing head.

[0028] Using the coordinates of the above precision control points and the established cam-connecting rod mechanism optimization equation, it can be determined that the length of crank 4 is equal to 39mm, the length of connecting rod 5 is equal to 106mm, the length of connecting rod 6 is equal to 478mm, the distance from point E on the plane of connecting rod 5 to hinge B is equal to 338mm, the length of cam push rod 8 is equal to 450mm, the angle between the line between hinge B and point E and the direction of connecting rod 5 is equal to 0.01rad, the installation angle of frame 10 is equal to 0.15rad, the x-axis coordinate of fixed hinge A is equal to 79mm, and the y-axis coordinate is equal to -299mm. When the cam-linkage mechanism passes through 20 precision control points, the lengths of the frame 10 are 484.8mm, 486.0mm, 484.6mm, 484.5mm, 485.0mm, 485.3mm, 484.6mm, 484.8mm, 485.0mm, 485.0mm, 485.0mm, 484.8mm, 483.8mm, 484.5mm, 485.8mm, 484.8mm, 484.7mm, 484.6mm, 484.9mm, and 485.6mm respectively.

[0029] According to the determined length dimensions of the rack at 20 precision control points, the equation R(θ A )=d(θ A )-1 can calculate the profile curve of cam 9. The crank 4 is driven at a constant speed, and the motion trajectory of point E on the plane of connecting rod 5 is obtained by motion simulation as follows: Figure 7 As shown in the figure, the average error between the trajectory of point E on the connecting rod 5 plane and the 20 precision control points is only 0.6mm, indicating that the cam connecting rod mechanism has a high trajectory reproduction accuracy. At the same time, the precision control points 2 to 7 on the horizontal straight line segment can completely coincide.

[0030] Furthermore, when the packaging object is a 2116-type PET transparent plastic fruit packaging box, the size of the cam linkage mechanism and the contour line of the cam 9 can also be determined according to the above equation. The length, width and height of the 2116-type PET transparent plastic fruit packaging box are 205mm, 155mm and 52mm respectively. According to the requirements of the heat sealing process, the heat sealing process can be divided into three steps, namely heating, heat preservation and pressure maintenance, slow separation and rapid retreat. Therefore, the target motion trajectory of the heat sealing head can be determined as follows Figure 8 The trajectory shown.

[0031] Similar to the packaging object of 1912 type plastic PP pallet, the target motion trajectory consists of three parts. The first part is the straight line part, which is used to control the heat sealing head to make horizontal uniform linear motion; the second part is the short arc part, which is used to control the slow separation of the heat sealing head and the packaging film; the third part is the long arc curve part, which is used to control the rapid retreat of the heat sealing head and pass over the packaged items.

[0032] There are 20 precision control points distributed on the target motion trajectory. The motion trajectory between precision control points 2 to 7 is a horizontal straight line, and the distances between precision control points 2 to 7 are equal, which is used to control the heat sealing head to move horizontally at a uniform speed. The motion trajectory between precision control points 7 to 9 is a short arc line, which controls the heat sealing head to separate slowly from the packaging film to avoid film tearing due to too fast separation speed. The motion trajectory between precision control points 9 to 20 is an arc curve, which is used for the rapid retraction of the heat sealing head.

[0033] Using the coordinates of the above precision control points and the established cam-connecting rod mechanism optimization equation, it can be determined that the length of crank 4 is 59.5mm, the length of connecting rod 5 is 135mm, the length of connecting rod 6 is 472mm, the distance from point E on the plane of connecting rod 5 to hinge B is 360mm, the length of cam push rod 8 is 450mm, the angle between the line from hinge B to point E and the direction of the connecting rod is 0.133rad, the installation angle of frame 10 is 0.2rad, the x-axis coordinate of fixed hinge A is 95mm, and the y-axis coordinate is -300m m, when the cam-linkage mechanism passes through 20 precision control points, the lengths of the frame 10 are 500.0mm, 501.3mm, 499.7mm, 499.7mm, 500.3mm, 500.5mm, 499.1mm, 500.1mm, 500.2mm, 500.0mm, 500.0mm, 499.4mm, 497.7mm, 498.7mm, 500.9mm, 500.1mm, 500.2mm, 500.2mm, 499.8mm and 500.0mm respectively.

[0034] According to the determined length dimensions of the rack 10 at the 20 precision control points, the equation R(θ A )=d(θ A )-1 can calculate the profile curve of cam 9. The crank is driven at a constant speed, and the motion trajectory of point E on the plane of connecting rod 5 is obtained by motion simulation as follows: Fig. 9 As shown in the figure. The average error between the precision control points is only 0.7mm, indicating that the cam-link mechanism has a high trajectory reproduction accuracy. At the same time, the precision control points 2 to 7 on the horizontal straight line segment can completely overlap. The crank is driven at 40 revolutions per minute, and the x-axis and y-axis speeds of point E on the connecting rod 5 plane are obtained as follows Fig.10 As shown. Between 1s and 1.29s, the speed in the x-axis direction is a horizontal straight line with a value of 358mm / s, while the speed in the y-axis direction is close to 0. Fig. 9 and Fig.10 It can be seen that the horizontal straight line segment of the motion trajectory of point E on the connecting rod plane 5 can not only completely coincide with the precision control point on the target trajectory, but also meet the requirements of uniform motion. 11 gives the principle diagram of the cam connecting rod mechanism suitable for 2116 type PET transparent plastic fruit packaging box. Fig.12A three-dimensional model of a cam-linkage mechanism suitable for a 2116 type PET transparent plastic fruit packaging box is given. In the figure, 11 is a heat sealing head and 12 is a conveyor belt. The above two specific embodiments are combined with the accompanying drawings to explain the implementation of the present invention in detail, but the present invention is not limited to the above implementation. Various changes can be made to it within the knowledge of ordinary technicians in this field. Therefore, the protection scope of the present invention is not limited to the above examples, and all technical solutions under the idea of ​​the present invention belong to the protection scope of the present invention.

Claims

1. A cam-connecting rod mechanism for a negative pressure fresh food packaging machine, comprising a crank (4), a connecting rod (5), a connecting rod (6), a fixed slide rail (7), a cam push rod (8), a cam (9), and a frame (10), wherein the cam (9) is fixedly connected to the crank (4) and pushes the cam push rod (8) to move back and forth along the frame (10), assuming that the length of the crank (4) is a, the length of the connecting rod (5) is b, the length of the connecting rod (6) is c, the length of the frame (10) is d, the distance from point E on the plane of the connecting rod (5) to hinge B is e, the length of the cam push rod (8) is l, and the angle between the line from hinge B to point E and the direction of the connecting rod (5) is θ E , the installation angle of the frame (10) is θ D , the rotation angle of the crank (4) is θ A , the coordinate of the fixed hinge A of the crank (4) is x A ,y A , the coordinates of the precision control points on the target trajectory are Then the Cartesian coordinates of point E on the connecting rod (5) plane can be expressed as, x E =x A +a·cos(θ A +θ D )+e·cos(θ B +θ E +θ D ) y E =y A +a·sin(θ A +θ D )+e·sin(θ B +θ E +θ D ) in, It is characterized by the lengths of the cam-link mechanism a, b, c, d, the distance e from point E to hinge B, and the direction angle θ E , the coordinate x of the fixed hinge A A ,y A , installation angle θ D , crank angle θ A , should satisfy the equation is the objective function, equation is the constrained optimization equation. In the constraint equation, [γ0] is the allowable transmission angle. At the same time, the radius of each point on the contour line of the cam (9) should satisfy the equation, R(θ A )=d(θ A )-l.

2. The cam-linkage mechanism according to claim 1, characterized in that: The length of the crank (4) is 39 mm, the length of the connecting rod (5) is 106 mm, the length of the connecting rod (6) is 478 mm, the distance from point E on the plane of the connecting rod (5) to the hinge B is 338 mm, the length of the cam push rod (8) is 450 mm, the angle between the line from the hinge B to point E and the direction of the connecting rod (5) is 0.01 rad, the installation angle of the frame (10) is 0.15 rad, and the x-axis coordinate x of the fixed hinge A is A Equal to 79mm, y-axis coordinate y A Equal to -299mm.

3. The cam-linkage mechanism according to claim 2, characterized in that: When the cam-link mechanism passes through 20 precision control points, the lengths of the frame (10) are 484.8mm, 486.0mm, 484.6mm, 484.5mm, 485.0mm, 485.3mm, 484.6mm, 484.8mm, 485.0mm, 485.0mm, 485.0mm, 484.8mm, 483.8mm, 484.5mm, 485.8mm, 484.8mm, 484.7mm, 484.6mm, 484.9mm and 485.6mm respectively.

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