Industrial robot operating machine design principles and design methods
1. The design principle of the operation machine
(1) The principle of minimum motion inertia Because there are many moving parts of the manipulator, and the motion state changes frequently, impact and vibration will inevitably occur. The principle of minimum inertia can increase the motion stability of the manipulator and improve the dynamic characteristics of the manipulator. Therefore, when designing, attention should be paid to reducing the mass of the moving parts as much as possible on the premise of satisfying the strength and rigidity, and paying attention to the centroid configuration of the moving parts on the rotating shaft.
(2) Scale planning optimization principle When the design requirements meet a certain working space requirement, the minimum boom size is selected through scale optimization, which will be conducive to the increase of the rigidity of the manipulator and further reduce the motion inertia.
(3) Principles for selection of high-strength materials Since the manipulator functions sequentially from the wrist, forearm, and arm to the base, it is necessary to select high-strength materials to reduce the quality of the parts.
(4) Principles of stiffness design In the design of manipulators, stiffness is a more important issue than strength. To maximize stiffness, the cross-sectional shape and size of the rod must be properly selected to increase the support stiffness and contact stiffness, and reasonably arrange the action on the arm The forces and moments on the rod minimize the bending deformation of the rod.
(5) Reliability principle The robot manipulator is particularly important because of its complicated mechanism and many links. Generally speaking, the reliability of components should be higher than the reliability of components, and the reliability of components should be higher than the reliability of the whole machine. The parts or structures whose reliability meets the requirements can be designed by a probabilistic design method, or the reliability of the manipulator system can be assessed by a comprehensive system reliability method.
(6) Technological principles The robot operating machine is a high-precision, highly integrated automatic mechanical system. Good processing and assembly manufacturability is one of the important principles to be reflected in the design. Only a reasonable structural design without good manufacturability will inevitably lead to a reduction in the performance of the operating machine and an increase in cost.
2. The design method and steps of the operation machine
(1) Determining the working objects and tasks Before starting to design the operating machine, first determine the working objects and tasks.
1) Welding task: If the work object is a car or a complex curved surface object, and the work task is to perform arc welding or spot welding on it, the manufacturing accuracy of the robot is required to be very high, and the arc welding task has a trajectory accuracy and Pose accuracy and speed stability have high requirements. The spot welding task has high requirements for the robot's pose accuracy. Both tasks require the robot to have the function of swinging the arc, while being able to freely in a small space Movement, with anti-collision function, so the robot has at least six degrees of freedom.
2) Painting task: If the work object is a car or a complex curved object, the task is to paint the interior of the car and the door or the surface of a complex curved object, the robot wrist must be flexible and able to be in a small space Free movement, with anti-collision function; the robot must be able to work stably and reliably for a long time; at the same time, the robot must have a smooth and streamlined outer surface, and the paint and gas lines should preferably pass through the inside of its cross arm and wrist to make the robot The surface is not easy to accumulate paint and dust, will not pollute the sprayed work objects, and the paint and gas pipelines are also not easy to damage; because the painting robot works in a flammable and explosive working environment, it must have an explosion-proof function. At the same time, the robot's trajectory accuracy, pose accuracy and speed stability also have high requirements. The robot should have at least six degrees of freedom.
3) Handling task: If the work object is bulky, the work task is fixed-point handling, and the positioning accuracy is high, then the robot's carrying capacity and positioning accuracy are high. If the work object is relatively light, the work task is also fixed-point transportation, but it is required to be handled lightly, and the positioning accuracy is required to be high, which has high requirements for the speed stability and positioning accuracy of the robot.
4) Assembly task: It has high requirements for the speed stability and pose accuracy of the robot.
Some robots can complete a variety of tasks, such as MOTOMAN-SKI20 series robots, which can be used for both handling and spot welding. They are fast, compact, powerful, and safe; another MOTOMAN-SK6 / SK16 The series of robots can perform a variety of tasks such as arc welding, handling, gluing, glaze spraying and assembly, and have the characteristics of high speed, compactness and high reliability.
When designing a new type of robot, it is necessary to fully consider the above factors, and should refer to advanced models of similar products at home and abroad, refer to its design parameters, and after repeated research and comparison, determine the characteristics of the required mechanical parts and determine the design plan.
Let's take a six-degree-of-freedom AC servo universal robot as an example to talk about the design process, as shown in Figure 14.
(2) Determine the design requirements
1) Load: According to the requirements of the user â€™s working objects and tasks, refer to the advanced models of similar products at home and abroad to determine the load of the robot. The load of general painting and arc welding robot is 5 ï½ž 6kg.
2) Accuracy: According to the requirements of the user â€™s working objects and tasks, refer to the advanced models of similar products at home and abroad to determine the maximum compound speed of the robot end and the maximum angular speed of each single axis of the robot.
3) Accuracy: According to the requirements of the user â€™s working objects and tasks, refer to the advanced models of similar products at home and abroad to determine the repeat positioning accuracy of the robot, such as the repeat positioning accuracy of the arc welding robot is Â± 0.4mm, Model 5003 developed by ABB The repeated positioning accuracy of the type painting robot is Â± 1mm. At the same time, it is necessary to determine the accuracy of the parts constituting the robot, the dimensional accuracy of the arm body, the shape and position accuracy, and the clearance of the transmission chain, such as the accuracy of the gear and the transmission clearance; also determine the accuracy of the components used on the robot, such as the transmission of the reducer Precision, precision of bearings, etc.
4) Teaching method: determine the teaching method of the robot according to the requirements of the user's working objects and tasks. The general robot teaching methods are as follows:
â‘ Offline teaching (offline programming);
â‘¡ Teaching by teaching box;
â‘¢Teaching by hand.
If it is a painting robot, it should have the function of manual hand-to-hand teaching, while for other robots, the first two functions are enough.
5) Work space: According to the requirements of the user's working objects and tasks, refer to the advanced models of similar products at home and abroad to determine the size and shape of the robot's working space.
6) Dimension planning: According to the requirements of the working space, refer to the advanced models of similar products at home and abroad, determine the length of the arm of the robot and the angle of the arm, and optimize the size.
(3) Coupling analysis of robot motion For most robots that are not directly driven, the motion of the front joint will cause additional motion of the rear joint, resulting in a motion coupling effect. For example, the motors of the six axes are all installed in the turret of the robot, and the design of other joints driven by chains, connecting rods or gears, and the design of the wrist joints driven by concentric gear sets will produce a kinematic coupling effect. In order to understand the coupling, when programming the robot kinematics control software, the following joints must be rotated by a corresponding number of revolutions to compensate. For a six-degree-of-freedom robot, if there is kinematic coupling between the 2 and 3 axes, and there is kinematic coupling between the 3, 4, 5, and 6 axes, then the 3, 4, 5, and 6 axes The motor must rotate the corresponding number of revolutions (sometimes forward, sometimes reverse, depending on the structure) to eliminate the effect of kinematic coupling, 3 axis to eliminate 2 axis, 4 axis to eliminate 2 axis and 3 axis , And so on, if you want to rotate forward, to 6 axes, the motor must have a very high speed to eliminate the influence of so many axes, sometimes the motor speed will not be enough, and there are too many axes with kinematic coupling relationship, the robot's Kinematic analysis and control will be very troublesome. Therefore, when designing a six-degree-of-freedom AC servo robot, under normal circumstances, the movements of the first four axes are designed to be relatively independent, and the kinematic coupling only occurs between 4, 5, and 6, that is, the movement of the five axes is The influence of the axis movement, the 6-axis movement is affected by the 4-axis and 5-axis movements. In this way, it can not only ensure the compactness of the mechanical structure, but also do not make most of the shafts with coupling relationship.
(4) Balance of the robot arm The advantages of balancing the gravity moment of the robot operating arm are as follows:
Â· If it is a paint spraying robot, it is convenient for teaching by hand.
Â· Make the driver basically only need to overcome the inertial force when the robot moves, and ignore the influence of gravity moment. Therefore, the driver with smaller volume and lower power consumption can be selected.
Â· Eliminate the danger of the robot arm hurting people under its own weight.
Â· In servo control, the influence of load change is reduced, so more accurate servo control can be realized.
Generally, the robot manipulator does not balance because the 1-axis turret rotates. The arms of the 4, 5 and 6 axes are often very small due to the gravity, and do not need to be balanced. Therefore, the gravity moment of the 2 and 3 axis arms is balanced. (Organized by China Educational Equipment Purchasing Network)
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