A method for selecting a spring-type balancing cylinder and a two-axis joint for an industrial robot

Abstract

The present invention relates to a spring-type balance cylinder for an industrial robot and a method for selecting a second-axis joint. The method for selecting a spring-type balance cylinder for an industrial robot and a second-axis joint according to the present invention includes: obtaining the normal start-stop torque rate η1 and the uniform motion load rate η2 of the motor in the second-axis joint according to T1, T2, T f , T 0max , T and i, and setting the selection constraint conditions of the motor and the reducer in the second-axis joint according to the model parameters of the motor and the reducer and η1 and η2. The present invention has the advantages of reducing the assembly difficulty and optimizing the second-axis joint part.

Description

Technical Field

[0001] The invention relates to the field of industrial robots, and in particular to a method for selecting a spring-type balancing cylinder and a two-axis joint of an industrial robot. Background Art

[0002] Industrial robots play an increasingly important role in industrial production. The center of gravity of the arm of an industrial robot does not pass through the joint axis, thus generating an eccentric moment. In a six-axis industrial robot, the second-axis joint bears the largest eccentric moment, so a balancing device is often installed at the second-axis joint, so that when the arm rotates a certain angle, the position change of the balancing device generates a balancing force that does not pass through the joint axis, thereby balancing the eccentric moment of the second-axis joint. This method can effectively reduce the motor load and extend the life of the reducer. The balancing devices on the market include counterweight type, spring type, hydraulic-pneumatic type, etc., among which the spring-type balancing cylinder is the most commonly used balancing device. Please refer to Figure 1 , which is an industrial robot with a spring-type balancing cylinder, includes a spring-type balancing cylinder 1, a large arm 2, a bracket 3, a two-axis joint 4 and a three-axis joint 5. One end of the spring-type balancing cylinder 1 is connected to the large arm 2 and supported by the bracket 3. The two-axis joint 4 and the three-axis joint 5 are respectively arranged at both ends of the large arm 2.

[0003] At present, when selecting spring balance cylinders, the spring stiffness and pre-compression parameters are often too large. According to the formula spring stiffness k = Gd 4 / (8nD 3 ), where G is the shear elastic modulus of the material, d is the spring wire diameter, n is the effective number of turns, and D is the center diameter. If a larger spring stiffness k is to be met, the spring wire diameter d is required to be increased, the effective number of turns n and the center diameter D are reduced, which greatly increases the manufacturing difficulty; at the same time, the pre-compression of the spring is large, and the force required to compress the spring is large, making the assembly difficult. At the same time, during the operation of the two-axis joint, the output torque of the motor exceeds the rated torque for a long time, and the service life is short. Retrieve relevant papers, such as "Tool Technology" 2014 Vol. 48 No. 12, which studied the parameters of the spring balance cylinder of the industrial robot. After simplifying the robot model, the influence of the relevant parameters of the spring balance cylinder on the unbalanced torque was discussed separately. The main research content is the influence of different parameters on the balance torque provided by the balance cylinder. The relevant data are all unbalanced torques at different angles when the upper arm is stationary, ignoring the influence of the motion state on the joint. The rated torque of the motor is less than the actual required torque, and the torque rate is high. Summary of the invention

[0004] Based on this, the purpose of the present invention is to provide a method for selecting a spring balancing cylinder and a two-axis joint of an industrial robot, which has the advantages of reducing the difficulty of assembly and optimizing the two-axis joint position.

[0005] A method for selecting a spring-type balancing cylinder and a two-axis joint of an industrial robot, the method comprising:

[0006] Step S1, simplify the structure of the industrial robot into a two-dimensional model, where the fulcrum of the spring-type balancing cylinder is A, the rotation center of the connection point between the spring-type balancing cylinder and the big arm is B, the two-axis joint rotation axis is C, the three-axis rotation axis on the big arm is D, and the length of AC is l 1 , BC length is l 2 ;

[0007] Step S2, determine the design parameters and structural parameters of the industrial robot, the design parameters include the set operating angle θ of the two-axis joint, the acceleration and deceleration time t and the two-axis joint speed n, the structural parameters include the weight m of the front end load of the two-axis joint, the maximum moment of inertia J, and the farthest distance l between its center of gravity and the rotation axis of the two-axis joint 0 ;

[0008] Step S3: Calculate the maximum torque T required for normal start and stop of the front end load of the two-axis joint according to the design parameters and structural parameters. 1 , the gravity moment T borne by the two-axis joint at any angle 2 and the maximum balancing torque T provided by the spring-type balancing cylinder within the operating angle range of the two-axis joint 0max ;

[0009] Step S4, obtaining the model parameters of the motor and reducer to be selected, the total friction torque of the motor and reducer is T f The model parameters of the motor include rated torque T, rated speed n e , maximum speed n 电机max and moment of inertia j, the model parameters of the reducer include: reduction ratio i, maximum allowable output speed n' max , start-stop allowable peak torque T e ', Instantaneous maximum allowable torque T' max ;

[0010] Step S5: According to T 1 、T 2 、T f 、T 0max , T and i obtain the normal start-stop torque rate η of the motor in the two-axis joint 1 and uniform motion load factor η 2 , according to the model parameters and η of the motor and reducer 1 With η 2 Setting selection constraints for the motor and reducer in the two-axis joint;

[0011] Step S6, according to the selection constraint condition, selecting from the motors and reducers to be selected one or more motor and reducer combinations that meet the selection constraint condition;

[0012] Step S7: Determine the constraint condition of the spring in the spring-type balancing cylinder, and according to the constraint condition of the spring and the balancing torque T provided within the operating angle range of the two-axis joint. 0 Obtain the parameter variable l of the spring balance cylinder 1 , l 2 , spring stiffness k 0 and spring precompression x 0 The value range of

[0013] Step S8, taking the sum of the absolute values ​​of the slope of the normal start-stop torque rate of the motor within the operating angle range as the characteristic of the motor start-stop torque rate fluctuation, selecting multiple groups of parameter variable values ​​in the value range, calculating the sum of the absolute values ​​of the slope of the normal start-stop torque rate of the motor within the operating angle range under different parameter variable value conditions for each group of the motor and reducer combination, and outputting the model of the motor and reducer and the value of the variable parameter when the sum of the absolute values ​​is at the minimum value.

[0014] The spring-type balancing cylinder and the selection method of the two-axis joint of the industrial robot described in the present invention select the motor and the reducer of the two-axis joint by balancing the torque, and optimize the motor with the minimum absolute value of the slope of the normal start-stop torque rate as the goal, so as to avoid the performance waste and cost increase caused by the selection being too large or too small, and the problem of the motor output torque approaching the maximum allowable torque during acceleration and deceleration, resulting in a decrease in service life. At the same time, by constraining the spring selection, the manufacturability is improved and the assembly difficulty is reduced.

[0015] Further, in step S1 , BC is perpendicular to CD.

[0016] Further, in step S2, the angle range of θ is θ∈[+a,-b], and when θ is zero, AB is parallel to the ground.

[0017] Further, in step S3, the maximum torque required for normal start and stop of the front end load of the two-axis joint is T 1 =J·2πn / t, the gravity moment borne by the two-axis joint at any angle is T 2 =mgl 0 sinθ, the maximum balancing torque T provided by the spring-type balancing cylinder within the operating angle range of the two-axis joint 0max =(1~1.5)·T 2max .

[0018] Further, in step S5, the normal start-stop torque rate of the motor is η1 =(T 1 +T 2 +T f -T 0max ) / (T·i), the uniform motion load rate of the motor is η 2 =(T 2 +T f -T 0max ) / (T·i), where T 2 =T 2max .

[0019] Further, in step S5:

[0020] The constraint condition of the motor is the normal start-stop torque rate η 1 ≤200%, the uniform motion load rate η 2 ≤80%; the actual maximum output speed N of the motor max =n·i≤the maximum speed n of the motor 电机max , the actual average output speed N of the motor m =i·(n·t+(a+b-nt)) / (2t+a+b-nt)≤rated speed n of the motor e , inertia ratio r = J / i 2 / j<10;

[0021] The constraint condition of the reducer is that the actual maximum speed n of the two-axis joint is less than the maximum allowable output speed n' of the reducer. max The actual start-stop maximum torque of the two-axis joint (including gravity torque) (T 1 +T 2 +T f -T 0max )≤the start-stop allowable peak torque T of the reducer e '; The maximum impact torque T of the two-axis joint em =(T 1 +T 2 +T f -T 0max ) / 0.05≤the maximum instantaneous allowable torque T' of the reducer max .

[0022] Further, in step S7, when the boom rotates, the spring-type balancing cylinder rotates around the fulcrum A, and the rotation center of the spring-type balancing cylinder and the boom connection point moves to B'. At this time, B'C = BC, the spring length increases, and the distance AB' The maximum compression required for the spring is x = l max -l 1 +l 2 +x 0According to the geometric relationship, the balancing torque T provided by the balancing cylinder within the operating angle range of the two-axis joint can be obtained. 0 =k 0 l 1 l 2 (x 0 +ll 1 +l 2 )|sinθ| / l, where k 0 is the spring stiffness, x 0 is the spring precompression, the T 0 The maximum value is T 0max .

[0023] Further, in step S7, the constraint condition of the spring is the spring pre-compression force k 0 x 0 ≤(200~800)N, where spring stiffness k 0 ≤(20~100), the actual maximum compression amount of the spring x'≥x.

[0024] Further, in step S8, the sum of the absolute values Among them, n is uniformly selected according to the size of the two-axis joint operation angle range. n Points, n n =(500-2000), and the normal start-stop torque rate value η of the motor corresponding to each point is obtained. i .

[0025] Furthermore, the method also includes step S9, checking the selected spring, and checking the fatigue strength and stability of the spring to ensure that the use requirements are met.

[0026] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of an industrial robot with a spring-type balancing cylinder;

[0028] Figure 2 A simplified two-dimensional model structure diagram of the industrial robot;

[0029] Figure 3 It is a simplified diagram of the structure after the big arm rotates;

[0030] Figure 4 This is a flow chart of a method for selecting a two-axis joint of an industrial robot with a spring-type balancing cylinder according to the present invention;

[0031] Figure 5 is a flow chart of the comparison process in step S8;

[0032] Figure 6 It is a curve diagram of the normal start-stop torque rate of the motor within the operating angle range. DETAILED DESCRIPTION

[0033] See also Figure 2-6 , Figure 2 A simplified two-dimensional model structure diagram of the industrial robot; Figure 3 It is a simplified diagram of the structure after the big arm rotates; Figure 4 This is a flow chart of a method for selecting a two-axis joint of an industrial robot with a spring-type balancing cylinder according to the present invention; Figure 5 is a flow chart of the comparison process in step S8; Figure 6 It is a curve diagram of the normal start-stop torque rate of the motor within the operating angle range.

[0034] The invention discloses a method for selecting a two-axis joint of an industrial robot with a spring-type balancing cylinder, comprising the following steps:

[0035] Step S1, simplify the structure of the industrial robot into a two-dimensional model, where the fulcrum of the spring-type balancing cylinder is A, the rotation center of the connection point between the spring-type balancing cylinder and the big arm is B, the two-axis joint rotation axis is C, the three-axis rotation axis on the big arm is D, and the length of AC is l 1 , BC length is l 2 , generally, line segment BC is perpendicular to line segment CD, and the initial position is that line segment AB is parallel to the ground.

[0036] Step S2, determining the design parameters of the industrial robot, the design parameters include the set operating angle θ of the two-axis joint, the acceleration and deceleration time t and the two-axis joint speed n, wherein the angle range of θ is θ∈[+a,-b], when θ is zero, the AB is parallel to the ground; determining the structural parameters of the industrial robot, the structural parameters include the weight m of the front end load of the two-axis joint, the maximum moment of inertia J, and the farthest distance l of its center of gravity relative to the rotation axis of the two-axis joint 0 .

[0037] Step S3: Calculate the maximum torque (excluding gravity moment) required for normal start and stop of the front end load of the two-axis joint as T 1 = J·2πn / t, and the gravity moment borne by the two-axis joint at any angle is T 2 =mgl 0 sinθ, the maximum balancing torque T provided by the spring-type balancing cylinder within the operating angle range of the two-axis joint 0max =(1~1.5)·T 2max .

[0038] Step S4, obtaining model parameters of the motor and reducer to be selected;

[0039] The model parameters of the motor include rated torque T, rated speed n e , maximum speed n 电机max and moment of inertia j;

[0040] The model parameters of the reducer include: reduction ratio i, maximum allowable output speed n' max , start-stop allowable peak torque T e ', Instantaneous maximum allowable torque T' max ;

[0041] According to the experimental results, the total friction torque of the motor and reducer under no-load conditions is T f .

[0042] Step S5, setting selection constraints for the motor and reducer;

[0043] The normal start-stop torque rate of the motor is η 1 =(T 1 +T 2 +T f -T 0max ) / (T·i), the uniform motion load rate of the motor is η 2 =(T 2 +T f -T 0max ) / (T·i), where the rated torque of the motor is T and the reduction ratio of the reducer is i;

[0044] The constraint condition of the motor is the normal start-stop torque rate η 1 ≤200%, the uniform motion load rate η 2 ≤80%; the actual maximum output speed N of the motor max =n·i≤the maximum speed n of the motor 电机max , the actual average output speed N of the motor m =i·(n·t+(a+b-nt)) / (2t+a+b-nt)≤rated speed n of the motor e , inertia ratio r = J / i 2 / j<10;

[0045] The constraint condition of the reducer is that the actual maximum speed n of the two-axis joint is less than the maximum allowable output speed n' of the reducer. max The actual start-stop maximum torque of the two-axis joint (including gravity torque) (T 1 +T 2 +T f -T 0max )≤the start-stop allowable peak torque T of the reducer e '; The maximum impact torque T of the two-axis jointem =(T 1 +T 2 +T f -T 0max ) / 0.05≤the maximum instantaneous allowable torque T' of the reducer max ;

[0046] In the constraints, T 2 =T 2max .

[0047] Step S6: According to the selection constraints of the motor and the reducer, one or more combinations of motors and reducers that meet the constraints are selected from the motors and reducers to be selected.

[0048] Step S7: When the boom rotates, the spring-type balancing cylinder rotates around the fulcrum A, and the rotation center of the spring-type balancing cylinder and the boom connection point moves to B'. At this time, B'C = BC, and the spring length increases, so the distance AB' The maximum compression required for the spring is x = l max -l 1 +l 2 +x 0 According to the geometric relationship, the balancing torque T provided by the spring-type balancing cylinder within the operating angle range of the two-axis joint can be obtained. 0 =k 0 l 1 l 2 (x 0 +ll 1 +l 2 )|sinθ| / l, where k 0 is the spring stiffness, x 0 is the spring pre-compression amount;

[0049] Determine the spring constraint condition as the spring pre-compression force k 0 x 0 ≤(200~800)N, where spring stiffness k 0 ≤(20~100) to reduce the difficulty of assembly; the actual maximum compression of the spring x'≥x, and the parameter variable l is obtained 1 , l 2 , k 0 、x 0 The value range of .

[0050] Step S8: To ensure that the robot's two-axis joint starts and stops smoothly within the operating range, the sum of the absolute values ​​of the slopes of the normal start-stop torque rates of the motors within the operating angle range is used as the characteristic of the motor start-stop torque rate fluctuation, and multiple groups of the parameter variables l are selected. 1 , l 2 , k 0 、x0 The value of each group of the motor and reducer combination is calculated under different conditions of the parameter variable values, and the absolute value of the slope of the normal start-stop torque rate of the motor within the operating angle range is calculated. Among them, n is uniformly selected according to the size of the two-axis joint operation angle range. n Points, n n =(500-2000), and the normal start-stop torque rate value η of the motor corresponding to each point is obtained. i , comparing and obtaining the model of the motor and reducer and the value of the variable parameter when the K value is the smallest;

[0051] The specific process of the above comparison is as follows: let the minimum K value be K min , first select a set of motor and reducer combinations, and set the minimum K value of the combination to be K 1 , obtain the values ​​of a set of parameter variables, and calculate a K value, denoted as K 11 , K 1 =K 11 , and then select the values ​​of the second set of parameter variables to calculate a K value, denoted as K 12 , compare K 12 With K 1 Get the minimum value and replace K with this minimum value 1 Then select the values ​​of the third set of parameter variables and convert the calculated K 1 The values ​​are compared, and so on, until all possible values ​​of the parameter variables are calculated, and the K corresponding to the motor and reducer combination of the group is obtained. 1 value, and make K min =K 1 If there are multiple motor and reducer combinations, then continue to select the second motor and reducer combination, and calculate the minimum K value K of the combination. 2 , the calculation process is the same as K 1 Similar, compare K 2 With K min , so that their minimum value replaces K min The value in , and so on, until the calculation of all the motor and reducer combinations is completed.

[0052] Step S9, when the output K value is the smallest, the models of the motor and reducer and the values ​​of the variable parameters are selected, and the selected spring is checked. The relevant calculation formula is detailed in GB / T 23935-2009, and the fatigue strength and stability of the spring are checked to ensure that the use requirements are met.

[0053] The spring-type balancing cylinder and the selection method of the two-axis joint of the industrial robot described in the present invention select the motor and the reducer of the two-axis joint by balancing the torque, and optimize the motor with the minimum absolute value of the slope of the normal start-stop torque rate as the goal, so as to avoid the performance waste and cost increase caused by the selection being too large or too small, and the problem of the motor output torque approaching the maximum allowable torque during acceleration and deceleration, resulting in a decrease in service life. At the same time, by constraining the spring selection, the manufacturability is improved and the assembly difficulty is reduced.

[0054] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and the present invention is also intended to include these modifications and modifications.

Claims

1. A method for selecting a spring-type balancing cylinder and a two-axis joint of an industrial robot, characterized in that: The method comprises: Step S1, simplifying the structure of the industrial robot into a two-dimensional model, wherein the fulcrum of the spring-type balancing cylinder is A, the rotation center of the connection point between the spring-type balancing cylinder and the boom is B, the two-axis joint rotation axis is C, the three-axis rotation axis on the boom is D, and the length of AC is l1, and the length of BC is l2; Step S2, determining the design parameters and structural parameters of the industrial robot, wherein the design parameters include the set operating angle θ, acceleration / deceleration time t and the rotation speed n of the two-axis joint, and the structural parameters include the weight m of the front end load of the two-axis joint, the maximum moment of inertia J, and the farthest distance l0 of its center of gravity relative to the rotation axis of the two-axis joint; Step S3: According to the design parameters and structural parameters, the maximum torque T1 required for the normal start and stop of the front end load of the two-axis joint, the gravity moment T2 borne by the two-axis joint at any operating angle, and the maximum balancing moment T provided by the spring-type balancing cylinder within the operating angle range of the two-axis joint are calculated. 0max ; Step S4, obtaining the model parameters of the motor and reducer to be selected, the total friction torque of the motor and reducer is T f The model parameters of the motor include rated torque T, rated speed n e , maximum speed n 电机max and moment of inertia j, the model parameters of the reducer include reduction ratio i, maximum allowable output speed n' max , start-stop allowable peak torque T e ', Instantaneous maximum allowable torque T' max ; Step S5: According to T1, T2, T f , T 0max , T and i to obtain the normal start-stop torque rate η1 and the uniform motion load rate η2 of the motor in the two-axis joint, and set the selection constraints of the motor and the reducer in the two-axis joint according to the model parameters of the motor and the reducer and η1 and η2; The constraints of the motor are: the normal start-stop torque rate η1≤200%, the uniform motion load rate η2≤80%; the actual maximum output speed N of the motor max =n·i≤the maximum speed n of the motor 电机max , the actual average output speed N of the motor m =i·(n·t+(a+b-nt)) / (2t+a+b-nt)≤rated speed n of the motor e , inertia ratio r = J / i 2 / j<10; The constraint condition of the reducer is that the actual maximum speed n of the two-axis joint is less than the maximum allowable output speed n' of the reducer. max The actual start-stop maximum torque of the two-axis joint (including gravity torque) (T1+T2+T f -T 0max )≤the start-stop allowable peak torque T of the reducer e '; The maximum impact torque T of the two-axis joint em =(T1+T2+T f -T 0max ) / 0.05≤the maximum instantaneous allowable torque T' of the reducer max ; Step S6, according to the selection constraint condition, selecting from the motors and reducers to be selected one or more motor and reducer combinations that meet the selection constraint condition; Step S7, determining the constraint conditions of the spring in the spring balancing cylinder, and obtaining the value ranges of the parameter variables l1, l2, spring stiffness k0 and spring pre-compression x0 of the spring balancing cylinder according to the constraint conditions of the spring and the balancing torque T0 provided within the operating angle range of the two-axis joint; Step S8, taking the sum of the absolute values ​​of the slope of the normal start-stop torque rate of the motor within the operating angle range as the characteristic of the motor start-stop torque rate fluctuation, selecting multiple groups of parameter variable values ​​in the value range, calculating the sum of the absolute values ​​of the slope of the normal start-stop torque rate of the motor within the operating angle range under different parameter variable value conditions for each group of the motor and reducer combination, and outputting the model of the motor and reducer and the value of the variable parameter when the sum of the absolute values ​​is at the minimum value.

2. The method for selecting a spring-type balancing cylinder and a two-axis joint of an industrial robot according to claim 1, characterized in that: In step S1 , BC is perpendicular to CD.

3. The method for selecting a spring-type balancing cylinder and a two-axis joint of an industrial robot according to claim 1, characterized in that: In step S2, the angle range of θ is θ∈[+a,-b], and when θ is zero, AB is parallel to the ground.

4. A method for selecting a spring-type balancing cylinder and a joint of an industrial robot according to any one of claims 1 to 3, characterized in that: In step S3, the maximum torque required for the normal start and stop of the front end load of the two-axis joint is T1=J·2πn / t, the gravity moment borne by the two-axis joint at any angle is T2=mgl0sinθ, and the maximum balancing torque T provided by the spring-type balancing cylinder within the operating angle range of the two-axis joint is 0max =(1~1.5)·T 2max .

5. The method for selecting a spring-type balancing cylinder and a joint of an industrial robot according to claim 4, characterized in that: In step S5, the normal start-stop torque rate of the motor is η1=(T1+T2+T f -T 0max ) / (T·i), the uniform motion load rate of the motor is η2=(T2+T f -T 0max ) / (T·i), where T2=T 2max .

6. The method for selecting a spring-type balancing cylinder and a joint of an industrial robot according to claim 5, characterized in that: In step S7, when the boom rotates, the spring-type balancing cylinder rotates around the fulcrum A, and the rotation center of the spring-type balancing cylinder and the boom connection point moves to B'. At this time, B'C = BC, the spring length increases, and the distance AB' The maximum compression required for the spring is x = l max -l1+l2+x0, according to the geometric relationship, the balancing torque T0 provided by the balancing cylinder within the operating angle range of the two-axis joint is obtained = k0l1l2(x0+l-l1+l2)sinθ / l, where k0 is the spring stiffness, x0 is the spring pre-compression, and the maximum value of T0 is T 0max .

7. The method for selecting a spring-type balancing cylinder and a joint of an industrial robot according to claim 6, characterized in that: In step S7, the constraint condition of the spring is that the spring pre-compression force k0x0≤(200-800)N, wherein the spring stiffness k0≤(20-100), and the actual maximum compression amount x'≥x of the spring.

8. The method for selecting a spring-type balancing cylinder and a joint of an industrial robot according to claim 7, characterized in that: In step S8, the sum of the absolute values Among them, n is uniformly selected according to the size of the two-axis joint operation angle range. n Points, n n =(500-2000), and the normal start-stop torque rate value η of the motor corresponding to each point is obtained. i .

9. The method for selecting a spring-type balancing cylinder and a joint of an industrial robot according to claim 8, characterized in that: The method further comprises step S9, checking the selected spring, and checking the fatigue strength and stability of the spring to ensure that the use requirements are met.

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