[Reprinted] design principles and methods for industrial robot operation machines

Article Reprinted from http://www.52robot.cn/bbs/viewthread.php? Tid = 319 & extra = Page % 3d1

Industrial Robot Operator

Operating Machine Design Principles and Methods
1. Operating Machine Design Principles
(1) the principle of minimum inertia is subject to impact and vibration due to frequent changes in the movement status due to the large number of moving parts of the operator. The principle of minimum inertia can increase the stability of the motion of the operator, improve the dynamics of the operating machine. Therefore, the design should pay attention to the premise of meeting the strength and stiffness, as far as possible to reduce the quality of moving parts, and pay attention to the configuration of moving parts on the center of the rotating shaft.
(2) Optimization Principle of scale planning when the design requirements meet certain workspace requirements, the minimum arm bar size is selected through scale optimization, which will be conducive to the improvement of the stiffness of the operator, the moment of inertia is further reduced.
(3) selection principle of High Strength materials because the operator operates from the wrist, arm, arm to seat in sequence as the load, it is necessary to choose high strength materials to reduce the quality of parts.
(4) Principle of stiffness design in the design of the operating machine, stiffness is more important to the strength. To maximize the stiffness, the profile shape and size of the member must be properly selected, increase the bearing stiffness and contact stiffness, reasonably arrange the force and torque acting on the arm, and minimize the bending deformation of the member.
(5) reliability principle the reliability problem is particularly important for the robot operator due to its complicated structure and many links. In general, the reliability of components should be higher than that of components, and the reliability of components should be higher than that of the whole machine. Parts or structures that meet the requirements of reliability can be designed through the probability design method, and the reliability of the operating machine system can be evaluated through the system reliability synthesis method.
(6) technology principle robot operator is a high-precision, high-integration automatic mechanical system. Good processing and assembly technology are one of the important principles to be embodied in the design. Only reasonable structure design without good workmanship will inevitably lead to the reduction of the operating machine performance and cost improvement.
2. design methods and steps of the operator
(1) Before determining the work object and task, you must first determine the work object and task.
1) welding task: if the working object is an automobile or an object with a complex curved surface and the task is to perform arc welding or spot welding, the manufacturing precision of the robot is required to be very high, the arc welding task has high requirements on the trajectory precision, pose precision, and speed stability of the robot. The spot welding task has high requirements on the robot's pose precision, both tasks require the robot to have the arc pendulum function, and to be able to freely move in a small space, with the anti-collision function. Therefore, the robot has at least six degrees of freedom.
2) painting task: if the work object is a car or an object with a complex surface, the work task is to spray the interior of the car and the surface of the door or complex curved objects, therefore, it is required that the robot's wrist should be flexible, be able to freely move in a small space, and be capable of anti-collision. The robot should be able to work continuously, stably and reliably for a long time; at the same time, it is required that the robot have a smooth and streamlined external surface. It is best to pass the paint and gas pipeline through its arm and wrist, so that the robot's external surface is not easy to accumulate paint and ash, and will not pollute the sprayed work objects, moreover, paint and gas pipelines are not easy to damage. Spray Paint robots work in inflammable and explosive working environments, so they must have explosion-proof functions. At the same time, it also has high requirements on the trajectory accuracy, pose precision, and speed stability of robots. The robot must have at least six degrees of freedom.
3) handling tasks: if the work object is heavy, the work task is fixed-point handling, and the positioning accuracy requirements are high, there are high requirements on the robot's carrying capacity and positioning accuracy. If the work object is relatively lightweight and the work task is also fixed-point handling, but it must be lightweight and the positioning accuracy must be high, there are high requirements for the speed stability and positioning accuracy of the robot.
4) Assembly tasks: high requirements on speed, precision, and pose accuracy of robots.
Some robots can complete a variety of work tasks, such as MOTOMAN-SKI20 series robots, can be used for both processing can also be used for spot welding, with fast, exquisite, strong and high security characteristics; another kind of MOTOMAN-SK6/sk16 series robot, can complete arc welding, transportation, gluing, spray glaze and assembly a variety of tasks, with high speed, exquisite and high reliability characteristics.
When designing a new type of robot, we should fully consider the above factors. We should also refer to the advanced models of similar products at home and abroad, refer to the design parameters, after repeated research and comparison, determine the characteristics of the desired mechanical part and determine the design scheme.
The following describes the design process with a six-degree-of-freedom AC Servo general robot, as shown in figure 14.
(2) Determine design requirements
1) load: Determine the robot load according to the user's work object and task requirements, and refer to the advanced models of similar products at home and abroad. Generally, the load of spray paint and arc welding robots is 5 ~ 6 kg.
2) precision: based on the requirements of the user's work objects and tasks, refer to the advanced models of similar products at home and abroad to determine the maximum composite speed and the maximum angular velocity of each single axis of the robot.
3) precision: based on the requirements of the user's work objects and work tasks, refer to the advanced models of similar products at home and abroad to determine the precision of repeated robot positioning, such as the accuracy of repeated positioning of arc welding robots is ± 0. 4mm, the precision of repeated positioning of the model 5003 spray paint robot developed by ABB is ± 1mm. At the same time, it is necessary to determine the accuracy of the parts that constitute the robot, the dimensional precision of the arm, the shape and position accuracy and the gap between the transmission chain, such as the accuracy of the gear and the transmission gap; it also determines the precision of the components used on the robot, such as the transmission precision of the reducers and the accuracy of the bearings.

4) Teaching Mode: Determine the robot teaching mode based on the user's work object and task requirements. Generally, robots can be taught in the following ways:
① Offline teaching (Offline Programming );
② Teaching box;
③ Manual teaching.
If it is a spray paint robot, it should have the manual hand teaching function, and for other robots, there are the first two functions.
5) Workspace: Determine the workspace size and shape of a robot based on the user's work object and task requirements and advanced models of similar products at home and abroad.
6) dimensional planning: according to the requirements on the workspace, refer to the advanced models of similar products at home and abroad, determine the length of the arm and the angle of the arm, and optimize the size.
(3) Robot Motion Coupling Analysis for most non-direct-driven robots, the motion of the front joint causes the additional motion of the rear joint and produces the motion coupling effect. For example, the six-axis motor is mounted in the turret of the robot, and the design of other joints is carried through the chain, connecting rod or gear transmission, and then the design of the wrist joint is carried by the concentric gear sleeve, it will produce a motion coupling effect. In order to decouple, when the robot's kinematics control software is compiled, the following joints need to be converted to a corresponding number to compensate. For a six-degree-of-freedom robot, if there is a motion coupling between the 2 and 3 axes, and there is a motion coupling between the 3, 4, 5, and 6 axes, so the 3, 4, 5, and 6-axis Motors must be converted to the corresponding number of turns (sometimes positive or reverse, depending on the structure) to eliminate the impact of motion coupling, 3 axis to remove 2 Axis, 4 axis to remove 2 Axis and 3 axis, and so on, if you want to forward to 6 axis, the motor must have a high speed to eliminate the influence of the multi-axis. Sometimes the motor's speed is not enough and there are too many axes with Motion Coupling Relationships, the robot's kinematics analysis and control will be very troublesome. Therefore, the design of a Six-Degree-of-Freedom AC Servo robot is generally designed to be relatively independent of the movements of the first four axes, the Motion Coupling only occurs between the 4, 5, and 6 axes, that is, the motion of the 5 axis is affected by the motion of the 4 axis, and the motion of the 6 axis is affected by the motion of the 4 axis and the 5 axis. In this way, both the Compact mechanical structure and the majority of coupling axes can be ensured.
(4) Balancing and balancing of the robot's arm the heavy torque of the robot's operating arm has the following advantages:
· For spray paint robots, manual hands can be easily taught.
· The actuator basically only needs to overcome the inertia force when the robot is moving, while ignoring the influence of Heavy torque. Therefore, you can choose a drive with a small volume and low power consumption.
· Eliminating the danger of dropping robots and hands under their own weight.
· Servo control can achieve more precise servo control because it reduces the impact of load changes.
Generally, the robot operator does not balance the rotation of the 1-axis turret. The arm of the 4, 5, and 6-axis is often not balanced because of its small gravity, therefore, it is necessary to balance the heavy torque of the 2 and 3 axes arm.
1) Weight balancing mechanism: This mechanism principle is shown in 2a. Set the arm weight to M1 and the weight to M2. The unbalanced torque is
M1 = m1glcos Gamma
The moment generated by the weight distribution is
M2 = m2gl 'cos Gamma
The static equilibrium condition is
M1 = m2
That is, m1l = m2l'

This balancing mechanism is simple, with good balancing effect, easy adjustment, and reliable operation. However, it increases the inertia of the arm and the load on the joints, and is suitable for situations where the imbalance torque is small.
2) Spring balancing mechanism: the principle 2b shows that the arm's unbalanced torque is
M1 = M11-M12 = mglcos gamma-ia
Medium M11-static unbalanced moment;
M12-inertial moment;
I -- moment of inertia of the arm against the joint axis;
A: average acceleration of arm motion.
The balancing moment generated by the spring is

Type K-spring stiffness;
L '-- distance from the spring Installation Point on the arm to the Joint Axis;
E -- distance from the installation point on the other end of the spring to the Joint Axis;
R -- free spring length.
The static equilibrium condition is
M2 = M11
The dynamic equilibrium condition is
M2 = M11 + M12
The balancing mechanism has a simple structure, good balance effect, and reliable operation. It is suitable for medium and small loads, but has a small balance range.
3) Cylinder balancing mechanism: shows the principle of this balancing mechanism 2C. Arm imbalance torque is
M1 = M11 + M12 = mglcos gamma + ia
The cylinder's equilibrium torque is

In formula F-cylinder piston thrust;
The other parameters are the same as above.
The static equilibrium condition is
M2 = M11
The dynamic equilibrium condition is
M2 = M11 + M12
The cylinder balancing mechanism is mostly used on heavy-duty handling and spot welding robot operating machines. The hydraulic pressure is small and the balancing force is large. The pneumatic pressure has good damping effect, but the volume is large.
(5) robot dynamics analysis the heavy torque of each axis has been basically balanced, so when these axes run, the motor mainly needs to overcome the Dynamic Torque brought about by the moment of inertia of each shaft.
1 axis: After analysis, when the robot's end reaches the farthest distance, the inertia of the 1 axis is the maximum. The calculation result shows that the moment of inertia of the 1 axis J1 is calculated. If the start time is T1, the dynamic torque is
M1 = J1 ω 1/T1
2-axis: After analysis, when the angle between the arm and the arm is the largest, the moment of inertia of the Two-axis is the largest. After calculation, the moment of inertia of the Two-axis is J2. If the start time is T2, the dynamic torque is
M2 = J2 ω 2/T2
3 axis: The Moment of Inertia between the robot arm and the upper center of the arm is the 3 axis of inertia. Likewise
M3 = J3 ω 3/T3
4-axis: 4-axis zero Torque balancing device, so the 4-axis motor should not only overcome the dynamic torque at startup, but also overcome the heavy torque caused by the wrist and load during operation. After calculation, the inertia of the 4-axis is obtained, and the transmission torque required for the 4-axis is calculated.
5 axis: 5 axis also has no heavy Torque balancing device, so the 5 axis motor is not only to overcome the dynamic torque at the start, but also to overcome the heavy torque caused by the wrist and load during operation. After calculation, the moment of inertia of the five-axis is obtained, and the transmission torque required for the five-axis is calculated.
6 axis: 6 axis also has no heavy Torque balancing device, so the 6 axis motor is not only to overcome the dynamic torque at the start, but also to overcome the heavy torque caused by the wrist and load during operation. After calculation, the moment of inertia of the six-axis is obtained, and the driving torque required for the six-axis is calculated.
(6) selecting an AC servo motor is the key to the design of the operating machine. Because the robot requires compact structure, light weight, and good motion characteristics, it is hoped that the weight of the motor should be light and the shape and size should be small under the same power. In particular, the motor mounted inside the robot's horizontal arm or vertical arm should be as light as possible, and the shape and size should be as small as possible.
Based on the transmission torque required for each shaft calculated by dynamics, divided by the deceleration ratio of the reductor, and then the efficiency of the transmission chain, such as the efficiency of the CER, the efficiency of the bearing and the efficiency of the gear, are taken into account, the motor can be selected based on the rotation speed required by each shaft (the coupling factor of motion should also be taken into account.
Note that the speed of the AC servo motor can be adjusted, and the torque output by the motor is constant within a considerable speed range, therefore, when using a motor, as long as the rated speed of the motor is greater than the maximum speed required by each axis.
At the same time, pay attention to the choice of the Position Encoder configured together with the AC servo motor, and indicate whether the motor needs to be equipped with a brake.
(7) Selection of the reducers used on the robot, the common ones are RV reducers and Harmonious Wave reducers.
RV reducers have long-term use without additional lubricant, long life, good rigidity, large reduction ratio, low vibration, high precision, convenient maintenance, and other advantages, suitable for use on robots. Its transmission efficiency is 0.8, which is very high compared with the gear group with the same deceleration ratio.
Its disadvantage is its heavy weight and large shape and size.
The advantage of harmonic reduction gear is light weight, small shape and size, large reduction ratio range, and high precision.
In robot design, RV reducers are generally used on the 1, 2, and 3 axes, and harmonic reducers are commonly used on the 4, 5, and 6 axes.
(8) The robot's arm should carry out the intensity check and stiffness check. When the strength and stiffness are met, the arm should use light materials as much as possible to reduce the inertia of motion, and reduce the pressure on the balancing mechanism.
(9) Check the parts of the Organization
1) bearing check: all the important bearings used in the design must go through the strength check. To meet the size and strength requirements, try to use domestic bearings to reduce the cost of robots.
2) axis check: all the important axes used in the design must pass the Strength Check and stiffness check.
3) gear selection: All the gears used in the design must undergo strength check.
4) Key and Spline: all the key and Spline used in the design must go through the intensity check.
5) pin and screw: all the more important pins and screws used in the design must go through the strength check.
(10) The design of the robot should take into account the convenience of processing and assembly, as well as the convenience of maintenance and adjustment.