A method for improving the impact force of a scissor lift mechanism

Abstract

The present invention discloses a method for improving the impact force of a scissor lift mechanism. The method controls a motor so that the motor rotates according to a certain function. The specific steps are as follows: 1) according to the user's requirement on the total time used for lifting the scissor lift mechanism, the lifting speed V is calculated. 举 ; 2) Lifting speed V 举 Converted into motor speed V 电 ; 3) The distance sensor measures the lifting height H; 4) Process the data and substitute H into the formula to get the motor speed V 电 The motor driver is used to issue a command to convert the electrode speed to V 电 The present invention ensures the uniform rise of the upper lifting platform by controlling the motor to move according to a certain function, thereby avoiding the excessive inertia force caused by the nonlinearity of the lifting speed of the scissor-type lifting mechanism, preventing the collapse of the overall structure, avoiding the collapse of the goods, improving the safety of operation and extending the service life of the lifting mechanism.

Description

Technical Field

[0001] The invention belongs to the technical field of AGV transportation, and in particular relates to a method for improving the impact force of a scissor-type lifting mechanism. Background Art

[0002] In recent years, with the gradual improvement of logistics-related infrastructure and the increasing development of network economic benefits, my country's smart logistics has developed rapidly. In the field of smart logistics, this requires that the logistics system should gradually develop towards automation, unmanned and intelligent.

[0003] In the process of smart logistics, smart warehousing is the most important and basic link. Whether smart warehousing is intelligent or not will greatly affect the development of smart logistics. It is urgent to develop a fully automatic warehousing system, design intelligent warehousing robots, and complete the operations of cargo shelving, picking, transportation, and packaging. In the development of smart warehousing, AGV has gradually occupied an important position. AGV refers to an automatic guided vehicle, which is equipped with an electromagnetic or optical guidance device and can automatically drive along a predetermined route. It also has a programming function and can drive along the path issued by the host computer or execute various instructions issued by the host computer. The mature development of AGV has become a great driving force for the rapid development of smart logistics.

[0004] In the process of rapid development of AGV, there are many types of AGV and working methods. For example, AGV can be divided into lurking, traction, dump, lifting and forklift types. Each type of AGV has its advantages and disadvantages and the working environment required by each type of AGV may be different. Therefore, in order to further realize high-efficiency and low-cost logistics operations on the basis of intelligence, standardized pallets came into being. The emergence of standardized pallets is conducive to standardizing and controlling the logistics process. Only on the basis of pallet standardization can the consistent operation of pallets be realized, making the logistics between production enterprises, logistics enterprises, wholesale enterprises and retail enterprises smoother, improving logistics efficiency and reducing logistics costs. On the other hand, since pallets have important connection operations in the logistics industry, the standardization and promotion of pallets are conducive to the integration of logistics equipment, infrastructure and logistics information systems related to standard pallets by logistics enterprises.

[0005] The working process of the pallet AGV is that the AGV automatically drives to the shelf according to the established route, and the shelf is placed with a cargo pallet. Then the AGV drives under the shelf, directly lifts the shelf and transfers it to the designated location. Due to the working principle of the pallet AGV, it has a smaller turning radius than the forklift AGV and the traction AGV, so the shelves can be placed more closely, bringing better space utilization.

[0006] However, the traditional pallet AGV still needs the cooperation of the shelf to realize the transfer of the pallet. Therefore, it is necessary to design an AGV that can get rid of the limitation of the shelf and obtain better space utilization. At present, there are pallet robots of this type on the market. Its structure consists of an E-shaped trolley body 1 and two sets of fork arms 2 installed in two blank slots of the E-shaped trolley body. Figure 1 shown.

[0007] The working process of the pallet robot is as follows: first, the AGV drives to the front of the cargo pallet placed directly on the ground according to the specified path; then the fork arm of the pallet robot moves horizontally relative to the body, moves to the appropriate position to insert into the bottom hole of the pallet and brakes; the scissor-type lifting mechanism on the fork arm lifts the pallet to a certain height above the vehicle body; the trolley moves horizontally relative to the fork arm to directly under the pallet; finally, the scissor-type lifting mechanism lowers the pallet and places it on the vehicle body, and transports the pallet to the target position according to the path.

[0008] During the lifting process, the fork arm lifting mechanism has three positions, namely the lowest position, the push position and the highest position. The lowest position is the normal height when the fork arm is not working, the push position is when the fork arm is raised to a certain height to touch the upper surface of the bottom hole of the pallet, that is, the height to lift the pallet off the ground, and the highest height is when the fork arm can lift the pallet to the maximum stroke.

[0009] At present, the control method of the fork arm motor is often to make it rotate at a simple uniform speed at the maximum speed of the motor. The disadvantage of this is that due to the principle of the scissor-type mechanism, the uniform rotation of the motor causes the lifting speed of the lifting platform to be nonlinear. This nonlinearity causes the lifting speed of the lifting platform to have acceleration. When the mass of the goods is large, the inertial force brought by the acceleration will be very large, causing a huge impact on the entire mechanism. In more serious cases, this inertial force exceeds the design strength of the entire scissor-type mechanism, causing failure of certain components in the mechanism and causing the overall structure to collapse, thereby causing the goods to fall and cause serious safety accidents. Summary of the invention

[0010] In view of the above-mentioned problems existing in the prior art, the purpose of the design of the present invention is to improve the impact force of the scissors-type lifting mechanism by changing the control method of the fork arm motor, so that the lifting platform of the scissors-type lifting mechanism has a uniform lifting speed, avoiding damage to the structure caused by additional inertia force.

[0011] The present invention is achieved through the following technical solutions:

[0012] A method for improving the impact force of a scissor lift mechanism, the scissor lift mechanism comprising a screw fixing seat, a ball screw, a micro guide rail, an outer scissor fork, an inner scissor fork, a motor, a reducer, a double connecting rod structure, a screw nut fixing seat, a screw nut, and a scissor mounting base plate, wherein the double connecting rod structure comprises a connecting rod 1 and a connecting rod 2. The method controls the motor so that the motor rotates at a certain function, and the specific steps are as follows:

[0013] 1) Calculate the lifting speed V according to the user's requirements for the total time used for the scissor lift mechanism to lift. 举 ;

[0014] 2) Lifting speed V 举 Converted into motor speed V 电 ;

[0015] 3) The distance sensor measures the lifting height H;

[0016] 4) Process the data and substitute H into the formula to get the motor speed V 电 The motor driver is used to issue a command to convert the electrode speed to V 电 .

[0017] Further, step 1) is specifically, according to the user's requirement on the total time used for lifting by the scissor lift mechanism, the lifting speed V is calculated according to formula (1): 举 , at this time the lifting speed is uniform,

[0018]

[0019] Among them, S is the maximum height that the scissors mechanism can lift, and t is the lifting time required by the user.

[0020] Further, step 2) is specifically as follows:

[0021] Set the lifting speed V 举 Substitute into equation (2), and set the screw nut fixing seat speed V G Converted into motor speed V through formula (3) 电 , we get the relation (4);

[0022]

[0023] V G =V 电 l (3)

[0024]

[0025] Furthermore, step 3) specifically measures the lifting height H by means of a TOF sensor installed on the scissor mechanism.

[0026] Further, step 4) is specifically as follows:

[0027] The lifting height H measured by the TOF sensor is sent to the lower computer of the fork arm, and the following control function is used to send a command to the motor controller to control the motor speed to change according to the function, so that the upper platform can move at a uniform speed at the speed required in step 1), thereby avoiding the harm of inertia force.

[0028]

[0029] Furthermore, in the above formula, S is the maximum height that the scissors mechanism can lift, t is the lifting time required by the user, l is the lead of the ball screw; L is half the length of the scissors arm; L1 is the length between the hinge point E and the hinge point O; L2 is the length of the second connecting rod; T is the height difference between the screw nut fixing seat and the lower hinge point of the scissors; α is the angle between the scissors and the horizontal direction; β is the angle between the second connecting rod and the horizontal direction.

[0030] Furthermore, the magnitudes of α and β and the lifting height H are related to each other in the following manner (5):

[0031]

[0032] The present invention ensures the uniform rise of the upper lifting platform by controlling the motor to move according to a certain function, thereby avoiding the occurrence of excessive inertia force due to the nonlinearity of the lifting speed of the scissor-type lifting mechanism, preventing the collapse of the overall structure, avoiding the collapse of goods, improving the safety of operation and extending the service life of the lifting mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the overall structure of the existing pallet robot;

[0034] Figure 2 It is a structural schematic diagram of a scissor-type lifting mechanism;

[0035] Figure 3 It is a structural schematic diagram of a double-link structure;

[0036] Figure 4 It is a schematic diagram of reaching the limit angle between the double-link structure;

[0037] Figure 5 It is a schematic diagram of the geometric relationship between the lifting speed of the lifting platform and the motor speed;

[0038] Figure 6 The geometric diagram of the scissor mechanism using the instantaneous center of velocity method;

[0039] Figure 7 It is a curve diagram of the relationship between lifting speed and lifting height;

[0040] Figure 8 This is the installation location diagram of the distance sensor.

[0041] In the figure, 1-trolley body, 2-fork arm, 3-screw fixing seat, 4-ball screw, 5-micro guide rail, 6-external scissors, 7-internal scissors, 8-motor, 9-reducer, 10-double connecting rod structure, 101-connecting rod one, 102-cam follower, 103-connecting rod one connecting piece, 104-connecting rod two, 105-connecting rod two connecting piece, 11-screw nut fixing seat, 12-screw nut, 13-scissors mounting base plate, 14-upper platform, 15-lower base, 16-TOF sensor. DETAILED DESCRIPTION

[0042] The present invention is described in further detail below in conjunction with the accompanying drawings in order to better understand the technical solution.

[0043] The scissor-type lifting mechanism studied in the present invention has a structural schematic diagram as shown in FIG. Figure 2 As shown, it specifically includes a screw fixing seat 3, a ball screw 4, a micro guide rail 5, an outer scissor fork 6, an inner scissor fork 7, a motor 8, a reducer 9, a double connecting rod structure 10, a screw nut fixing seat 11, a screw nut 12, and a scissor fork mounting base plate 13. The structural schematic diagram hides the upper platform and lower base plate of the scissor fork lifting mechanism. The scissor fork mounting base plate 13 is installed on the lower base plate, and the screw fixing seat 3 and the micro guide rail 5 are both installed on the scissor fork mounting base plate 13; the screw nut 12 and the screw nut fixing seat 11 are threadedly connected to transmit torque, and the guide rail slider on the micro guide rail 5 is installed under the screw nut fixing seat 11.

[0044] The working principle of the mechanism is as follows: the motor 8 amplifies the torque under the action of the reducer 9, driving the ball screw 4 to perform a rotary motion. Since the screw nut 10 is fixed on the screw nut fixing seat 11, and the screw nut fixing seat 4 can only move horizontally under the action of the micro guide rail 5, the rotary motion of the ball screw 4 is converted into a linear motion of the screw nut fixing seat 11 along the micro guide rail 5. The screw nut fixing seat 11 is hinged with the double connecting rod structure 10, so the double connecting rod structure moves with the screw nut fixing seat, and the double connecting rod structure 10 is hinged with the inner scissor fork 7. The inner scissor fork 7 and the outer scissor fork 6 are also hingedly connected. Due to the movement of the double connecting rod structure, the angle between the inner scissor fork and the outer scissor fork changes, realizing the lifting and lowering of the scissor-type lifting mechanism.

[0045] The structural schematic diagram of the double connecting rod structure 10 is shown in FIG. Figure 3 As shown, the cam follower 102 is fixedly connected to the connecting rod 101 by welding, and the connecting rod 1 connecting piece 103 and the connecting rod 2 connecting piece 105 are respectively connected to the two connecting rods 101 and 104 by threads.

[0046] When the double-link structure 10 moves under the push of the screw nut fixing seat 11, first, under the action of the gravity of the heavy object, the connecting rod 1 101 and the double-link structure 10 only move horizontally to reach the limit angle. The role of the six cam followers 102 is to support the connecting rod 1 101 at this time, and the connecting rod 2 104 rotates relative to the connecting rod 1 101. At this time, the rotation of the connecting rod 2 104 will cause the angle between the inner and outer scissors to change, and the height of the upper platform of the lifting mechanism will gradually increase. When the upper platform contacts the bottom hole of the pallet and is about to bear the weight, the position of the double-link structure 10 is called the push position; when the screw nut fixing seat 11 continues to move, the scissors-type lifting mechanism lifts the pallet off the ground and continues to rise. At this time, the double-link structure reaches the limit angle, which is called the limit position. The schematic diagram of the limit position is shown in FIG. Figure 4 After reaching the limit position, the height of the lifting mechanism continues to increase. At this time, the connecting rod 101 no longer moves horizontally, and there is no mutual movement between the connecting rod 101 and the connecting rod 2 104. The double connecting rod structure 10 can be equivalent to a rod, and the two ends of the rod are the two ends of the connecting rod 101 and the connecting rod 2 104 that are not connected to each other. Under the action of this equivalent rod, the lifting height of the scissors continues to increase until the highest height that the mechanism can reach, and this position is called the highest position.

[0047] The structure is analyzed to obtain the relationship between the lifting speed of the lifting platform and the motor speed. The geometric relationship diagram of the structure is shown in Figure 5 As shown. Among them, AC rod is the external scissor fork, BD rod is the internal scissor fork, EG rod is the second connecting rod, and GF rod is the first connecting rod. The size relationship is that the length of the internal and external scissor forks is 2L, and point O divides the scissor forks equally; L1 is the length from the hinge point of connecting rod 2 and the internal scissor fork to point O, and L2 is the length of connecting rod 2; T is the distance from the hinge point of the screw nut fixing seat and connecting rod 1 to the hinge point at the bottom of the scissor fork; α is the angle between the scissor fork and the horizontal direction; β is the angle between connecting rod 2 and the horizontal direction.

[0048] In this geometric relationship, there are some relationships as follows. From the relationship (5), we can get that the size of α and β is related to the lifting height H:

[0049]

[0050] In this geometric relationship, the instantaneous center of velocity method is used. The instantaneous center of velocity refers to the point in the plane motion of a rigid body where the instantaneous velocity is 0. Applying the instantaneous center of velocity method to this mechanism yields Figure 6 . Figure 6 The velocity of point B is V B It is the vertical lifting speed of the lifting platform, the G point speed V G is the horizontal moving speed of the screw nut fixing seat. The speeds of the hinge points E and O are V E and V OUsing the velocity instantaneous center method, we know that the velocity instantaneous center of the scissor arm BD rod is point A, and the velocity instantaneous center of the connecting rod EG rod is point K. According to the principle of similar triangles and geometric relationships, the lifting speed V B and slider moving speed V G The specific derivation process is as follows:

[0051] According to the similar triangle principle of △AED and △EIK, L AE and L KE The relationship is as follows (6):

[0052]

[0053] The velocity V of the hinge point E is calculated according to the velocity instantaneous center method E and the moving speed V of the screw nut fixing seat G The relationship is as follows (7):

[0054]

[0055] Apply the velocity instantaneous center method to the BD rod to calculate the velocity V of the hinge point E E and lifting speed V B The relationship is as follows (8):

[0056]

[0057] Finally, the moving speed V of the screw nut fixing seat is obtained G and lifting speed V B The relationship is as follows (9):

[0058]

[0059] According to the geometric relationship, the length of each segment is calculated as follows (10):

[0060]

[0061] Bring the length of each section into the moving speed V of the screw nut fixing seat G and lifting speed V B The final expression is as follows:

[0062]

[0063] Assuming that the motor speed is a constant, the relationship between the motor speed and the horizontal moving speed of the screw nut fixing seat is as follows (3). It can be obtained that when the motor speed is a constant, the horizontal moving speed of the screw nut fixing seat is also a constant.

[0064] V 丝 =V电 l(3)

[0065] Among them, V 丝 is the horizontal moving speed of the screw nut holder, that is, V in the figure above G ; V 电 is the speed of the motor; l is the lead of the screw.

[0066] Substitute the specific values ​​of the scissor mechanism studied in this application into formula (2), and take a point every 1 mm from the lowest height to the highest height according to the scissor height, calculate α and β according to formula (5), and let the motor move at a uniform speed at the highest speed, and the lifting speed V of the lifting mechanism can be obtained. B The variation curve of the lifting height of the scissor lift mechanism is as follows: Figure 7 shown.

[0067] according to Figure 7 It can be seen that when the motor speed is constant, the lifting speed of the upper platform is decreasing as the lifting height increases. Since the lifting speed changes, its rate of change is acceleration, which proves that when the motor speed is constant, the upper platform is rising at a certain acceleration. At this time, the acceleration will bring a certain inertia force. When the mass of the goods is large, this inertia force will become so large that it exceeds the design strength of the mechanism, thus causing serious safety accidents.

[0068] Based on this, the present application proposes a motor control method, which allows the motor to rotate according to a certain function, so that the lifting speed can be kept constant and the harm caused by inertia force can be avoided. The specific steps are as follows:

[0069] 1) According to the user's requirement for the total time used for lifting, the lifting speed is calculated according to the following formula (1), and the lifting speed is uniform at this time.

[0070]

[0071] Wherein, S is the maximum height that the scissor lift mechanism studied in the present invention can lift, and t is the lifting time required by the user.

[0072] 2) Substitute the lifting speed into formula (2), V 举 That is V B , the screw nut fixing seat speed V G Converted into motor speed V through formula (3) 电 The relationship obtained is as follows:

[0073]

[0074] Since the magnitude of α and β in the above formula is related to the lifting height H, that is, formula (5), it is necessary to use a distance sensor to measure the lifting height of the scissor lift mechanism. The installation position of the distance sensor is as follows: Figure 8 As shown, the TOF sensor 16 is a laser distance sensor installed on the lower base 15 of the fork arm, and can measure the distance from the lower base 15 to the plane of the upper platform 14, that is, the lifting height H

[0075] The lifting height H is measured by the TOF sensor 16, and the data is sent to the lower computer of the fork arm. Through the following control function, a command is sent to the controller of the motor to control the motor speed to change according to the function, so that the upper platform can move at a uniform speed at the speed required in step 1), thereby avoiding the harm of inertia force.

[0076]

[0077] Among them, S is the maximum height that the scissors-fork mechanism studied in the present invention can lift, t is the lifting time required by the user, l is the lead of the ball screw; L is half the length of the scissors-fork arm; L1 is the length between the hinge point E and the hinge point O; L2 is the length of the connecting rod 2; T is the height difference between the screw nut fixing seat and the lower hinge point of the scissors-fork.

[0078] The present application can keep the lifting speed of the upper platform of the scissor mechanism uniform by controlling the motor speed. Since most motors currently only control the motor to rotate at a simple uniform speed, the lifting speed of the upper platform is nonlinear, and the inertial force caused will cause harm to the mechanism. This control method avoids the influence of the inertial force by uniformly moving the upper platform.

Claims

1. A method for improving the impact force of a scissor lift mechanism, the scissor lift mechanism comprising a screw fixing seat, a ball screw, a micro guide rail, an outer scissor fork, an inner scissor fork, a motor, a reducer, a double connecting rod structure, a screw nut fixing seat, a screw nut, and a scissor mounting base, wherein the double connecting rod structure comprises a connecting rod 1 and a connecting rod 2, and is characterized in that This method controls the motor to rotate according to a certain function. The specific steps are as follows: 1) Calculate the lifting speed V according to the user's requirements for the total time used for the scissor lift mechanism to lift. 举 ; 2) Lifting speed V 举 Converted into motor speed V 电 , specifically: Set the lifting speed V 举 Substitute into equation (2), and at the same time change the screw nut fixing seat speed V G Converted into motor speed V through formula (3) 电 , we get the relation (4); ； 3) The distance sensor measures the lifting height H; 4) Process the data and substitute H into the formula to get the motor speed V 电 The motor driver is used to issue a command to convert the electrode speed to V 电 , specifically: The lifting height H measured by the TOF sensor is sent to the lower computer of the fork arm, and the following control function is used to send a command to the motor controller to control the motor speed to change according to the function, so that the upper platform can move at a uniform speed at the speed required in step 1), thereby avoiding the harm of inertia force. ； S is the maximum height that the scissors mechanism can lift, t is the lifting time required by the user, and is the lead of the ball screw; L is half the length of the scissors arm; L1 is the length between the hinge point E and the hinge point O; L2 is the length of the second connecting rod; T is the height difference between the screw nut fixing seat and the lower hinge point of the scissors; α is the angle between the scissors and the horizontal direction; β is the angle between the second connecting rod and the horizontal direction.

2. A method for improving the impact force of a scissor lift mechanism as claimed in claim 1, characterized in that Step 1) Specifically, according to the user's requirement for the total time taken for the scissor lift mechanism to lift, the lifting speed V is calculated according to formula (1): 举 , at this time the lifting speed is uniform, ； Among them, S is the maximum height that the scissors mechanism can lift, and t is the lifting time required by the user.

3. A method for improving the impact force of a scissor lift mechanism as claimed in claim 1, characterized in that Step 3) specifically measures the lifting height H by using a TOF sensor installed on the scissor mechanism.

4. A method for improving the impact force of a scissor lift mechanism as claimed in claim 1, characterized in that The magnitude of α and β and the lifting height H are related by the following equation (5): 。

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