The process of designing industrial robots is so easy!

      The industrial robot design process is really easy!

The design of industrial robots is the same  as most mechanical design processes. First of all, you need to know why you want to design a robot ? What functions can the robot achieve? How big is its activity space (effective working range)? After understanding the basic requirements, the next step will be easy.

　　First, the type of robot is determined based on the basic requirements, whether it is a walking lifting (lifting) robot arm, a three-axis coordinate robot, a six-axis robot, etc. Once the type of robot is selected, the control method is determined, there is a guiding direction for designing in a limited space.

　　The next thing to do is to determine the design task. This is a relatively complex process. The first step in implementing this complex process is to clearly define the design requirements; the second step is to make a mechanical transmission diagram according to the design requirements, analyze the diagram, formulate an action flow chart (diagram), preliminarily determine the transmission power, control process method; the third step is to clarify the design content, design steps, points to overcome, design calculations, sketches, materials, processing technology, control procedures, circuit diagrams; the fourth step is to comprehensively review all aspects of the content confirm production.

　　Below I will use a six-axis industrial robot as a design object to illustrate this design process:

　　Before introducing robot design , let me talk about the application field of robots. The application field of robots can be said to be very wide. There are many examples in automated production lines, such as palletizing robots, packaging robots, line transfer robots; there are also many examples in welding, such as welding robots on automobile production lines , etc. Now the development of robots is very rapid, the application of robots has also been extended to various industries in civilian enterprises. The demand for robot design talents is also increasing.

　　The application scope of six-axis robots is different, the design forms are also different. There are many companies producing robots in the world now, each has its own unique structure. The most widely used robots in China include: ABB, Panasonic, FANUK, Motoman other imported robots.

　　Although robots are widely used, there are no well-known manufacturers in my country. This is a question worth pondering for Chinese mechanical engineers! Are there too few discussions on robot technology? Are there enough practitioners to form a group? Although there are discussions about robots in many places, there is no real popularization.

　　Since we are going to talk about design, I will start the beginning talk about it step by step. I will try my best to make it simple clear. Please correct me if I am wrong!

　　The six-axis robot is a multi-joint, multi-degree-of-freedom robot with many movements flexible changes. It is an industrial robot with high flexibility technology the widest application. So how to design it scratch? How to determine the working range? How to arrange the movements? How to control the posture? What are the requirements for the joints of each part? so on. . . . . . Let's move on slowly with many questions!

　　First, we set: the robot is a six-axis multi-degree-of-freedom robot, with a gripper holding a standard welding gun for oxygen-shielded welding; it can complete spot welding, continuous welding other welding parts with different requirements, automatic production lines with fast-changing process requirements process routes. The maximum extension is 1700mm; it rotates 270 degrees; the base is fixed horizontally with the horizon; it is fully motor-driven.

　　Well, with such basic requirements, we can start to think about the preliminary plan.

　　First of all, it is fully motor-driven, so when considering the solution, we should consider the various hydraulic pneumatic structures, that is, the transmission mechanism can only use mechanical mechanisms such as gear racks connecting rod mechanisms.

　　Robots are used for welding, so we will examine various welding techniques methods under manual behavior. There is a very complicated thing here, that is, welding technology; since the welding technology cannot be determined, we will distinguish it. Commonly used welding includes single-point spot welding, continuous discontinuous spot welding, continuous flat seam welding, fillet welding, vertical seam welding, overhead welding, circumferential seam welding, etc. . . . . .

　　After understanding various welding methods, you will also understand that to achieve these complex actions, you need a set of feasible control methods. Before the machine is completely designed, you don’t need to think too much about the control plan. It is enough to have a rough outline concept. After the mechanical structure is completed the driving power of various aspects is determined, you can do the detailed program.

　　The welding gun is a commonly used standard welding gun, which means that the welding gun can be replaced at any time, which requires us to quickly lock release the clamping part of the welding gun.

　　The welding gun needs to adjust various welding postures during the welding process, so the mechanical wrist must be very flexible adjustable in all directions angles.

　　With the above basic requirements set conditions, the scheme reasoning has become organized. Next, we will clarify the design requirements so that the design direction will deviate too much.

　　Design Tasks

　　Design requirements: The robot is suitable for the welding field can complete various welding actions; in order for the robot to adapt to various welding processes, the online process adjustment is fast, a flexible control program is used when compiling the control program, an adaptive online offline teaching program is used; the weld, weld pool, weld bead are imaged tracked, various parameters of the welding machine are automatically adjusted.

　　The robot is fully servo-driven fixed on the ground. It has six-axis control, each joint has flexible movement. The range of motion of each axis is designed according to the process description table, the mechanism is as compact as possible the overall appearance is beautiful.

　　design content

　　Mechanical design: Design the mechanical structure of each joint according to the design requirements process description, determine the material processing technology of each component; prepare calculations, verify the mechanical strength, drive power given grasping (lifting) weight, inertia calculation of each motion path, control calculation of posture. Verify the service life of each key component of the robot. Combine the control program circuit to prepare the robot maintenance manual.

　　Program control design: Design the control process according to the design requirements the process route finally formulated by the mechanical engineer; design the robot motion program in combination with the mechanical structure drive signal feedback methods; the program should have adaptive functions, automatic fixed-point tracking, real-time monitoring of the welding machine current voltage, automatic adjustment; use imaging monitoring identification technology for welds weld pools.

　　Design Circuit Diagram

　　With such a file, it will be easier for us to design; then the first thing we need to do is: draw a simple diagram of the robot's movement, plan the robot's movement trajectory, after doing these, we can design the mechanical structure consider the program circuit diagram.

Robot movement diagram:

　　After we draw a simple diagram of mechanical movement, we usually analyze the diagram first; although the simple diagram cannot fully reflect the composition of the mechanical structure, it shows the overall outline of the object to be designed.

　　So for our robot diagram, should we start to analyze it reasonably?

　　First, let's look at the design brief, which shows that three of the six axes are for rotational motion, the rest are for angular motion.

　　In combination with the task book, we look at the schematic diagram to see whether the 1st, 4th 6th axes are capable of rotation. In other words, we need to check whether the schematic diagram we drew is consistent with the requirements in the task book. If it is consistent, it means that our design ideas are consistent with the requirements (customer requirements) we can proceed to the next step. If , we have to redraw the schematic diagram.

　　As can be seen the simple diagram, the robot's arms have a large range of extension retraction; if the arms are fully extended, we assume that they are the same steel body, this will form a cantilever beam with one end fixed.

　　 the analysis of beams in the applied mechanics knowledge system, we know that to understand the deformation of a cantilever beam, we must first know the weight cross-sectional inertia of the beam.

　　As can be seen the simple diagram, due to the multiple joint connections, it is easy to know the cross-sectional shape inertia. Only after all the mechanisms are designed can we know the desired parameters.

　　As can be seen the diagram, the second axis is responsible for the up down movement of the arm, the arm is relatively long, so there must be an inertial impulse during the movement. That is to say, when the arm moves very slowly, the inertia is very small; if the speed increases, the inertia increases, this inertial impulse has a linear relationship with the speed; how to maintain a certain speed without changing the inertia? As we all know, increasing damping can effectively eliminate this relationship. In this way, everyone can understand the purpose of the two springs in the diagram.

　　In this case, we will start designing the wrist, which is also known as the top-to-bottom design method.

　　What issues should be considered when designing a wrist? We know that there is a welding gun, which is very heavy, a hand gripper is required to hold the welding gun. In other words, the load on the wrist when it rotates is large, so it is sufficient to choose a component with low driving power.

　　The wrist needs to rotate within a range of 360 degrees, there must be a joint behind it that swings up down; the wrist is at the front end of the robot arm, so of course the overall mass cannot be too heavy.

　　Planetary gear transmission has a large transmission ratio, a complex structure, a clearance between gear pairs, which cannot be self-locking. If it is used, the gear accuracy must be improved. Since it is a precision transmission, the gear material cannot be selected according to the conventional gear material, the processing technology is much more complicated than that of conventional gears.

　　Cycloid pinwheel transmission has a large transmission ratio, complex structure, small transmission gap, can be self-locking. If it is adopted, the size of the wrist will be too small, the parts are difficult to process the accuracy is easy to guarantee.

　　After comparing various aspects, it was decided to adopt a planetary gear transmission mechanical structure. Planetary gears have assembly clearance clearance caused by mechanical wear during transmission; to eliminate these mechanical clearances, the first thing to do is to make the matching clearance of the gear pair small, the surface of the gear material should be wear-resistant after heat treatment. Therefore, the design calculation of the planetary gear pair cannot be calculated according to the design method of conventional planetary gears. The robot's wrist is a very flexible joint, it needs to rotate in both positive negative directions. How to install the motor is a problem; the connection between the planetary gear transmission mechanism the wrist pitch joint is a problem.

　　In addition, the wrist movement speed may be non-uniform; how to control the motor? How to collect feedback signals? Is there any external interference in the process of sending control signals to the execution unit? does it come ?

　　Another thing is the accuracy of the wrist during movement. How to achieve the movement accuracy when the wrist moves relative to the space? What are the factors that affect the movement accuracy?

　　Before designing the wrist, you must understand the various factors contents that affect the wrist. Only after the problems are answered can you actually start designing the wrist.

　　The technical parameters of the servo motor are given below:

　　Model:MSMD04ZS1V

　　Rated output power: 400W

　　Rated torque: 1.3Nm Torque: 3.8Nm

　　Rated speed/maximum speed: 3000/5000rpm

　　Motor inertia (with brake): 1.7×10-4Kg.m2

　　Transformer capacity: 0.9KVA

　　Encoder : 17 bits (resolution: 131072). 7-wire incremental/absolute.

　　Applicable driver model: MBDDT2210

　　Since we have chosen planetary gear transmission, we need to perform relevant calculations for the planetary gears.

　　First, the modulus. Since the structure of the robot wrist is required to be as small as possible, the output torque is very large. However, it is possible to commutate at high speed in both the positive negative directions. That is to say, the gears have to overcome a large inertia force when commutating. Therefore, the selection calculation of the modulus should be calculated according to the multiple of the output torque. That is to say, when calculating the modulus according to strength, the safety factor should be larger. At the same time, due to structural limitations, try to use a small modulus. You can refer to the "Gear Design Manual" for the calculation formula of the gear. Here I choose the modulus as: 1m. After selecting the modulus, the transmission ratio will be calculated. For the calculation of planetary gear transmission, you can refer to the "Gear Design Manual" the "Gear Transmission Section" in the "Mechanical Design Manual", which contains detailed introductions calculation examples. I will introduce quote it here.

　　In planetary gear transmission, there must be a floating structure. Is this also applicable to the robot wrist? Which part does the output? Which part is floating?

　　First, the robot wrist can rotate 360 degrees has a relatively small structure. Second, its output part needs to have a flange for installing the clamping actuator.

　　If the planet carrier is allowed to float, the planetary gears are distributed on the circumference of the sun gear. When it is allowed to float, it does rotate around the fixed axis during operation, that is, it does meet the rotation conditions of the output flange.

　　Now let's consider letting the internal gear rotate the flange is fixed on the internal gear, so that the rotation conditions of the flange can be guaranteed.

　　The following is a diagram of the wrist structure, with no floating parts internal gears rotating.