I. Background of the development of industrial robots
The term ROBOT was first used in 1920 by Czech playwright Karilo Chibek in his science fiction play Rossum's Universal Robots, and has since become synonymous with robotics.
In March 1938, The Meccano Magazine reported on a model of a handling robot, one of the earliest reports of a model robot aimed at industrial applications. Designed by Griffith P. Taylor in 1935, it was capable of five axes of motion by means of a single electric motor. By 1954, the first electronically programmable industrial robot was designed by G.C. Devol in the United States. And in 1960, the American company AMF produced the column-coordinate Versatran robot with point and trajectory control, which was the world's first robot used in industrial production.
In 1974, Cincinnati Milacron successfully developed a multi-jointed robot. By 1979, Unimation launched the PUMA robot, which is a multi-joint, all-motor drive, multi-CPU secondary control of the robot, the use of VAL special language, can be equipped with visual, tactile, force sensors, at that time is the most technologically advanced industrial robots. Today's industrial robots are largely based on this structure. This period of the robot belongs to the "Teach-in/Playback" (Teach-in/Playback) type robots, only with memory, storage capacity, according to the corresponding program to repeat the operation, the surrounding environment basically has no perception and feedback control capability.
Into the 80s, with the development of sensing technology, including visual sensors, non-visual sensors and information processing technology, the second generation of robots - sensory robots. It is able to obtain part of the relevant information about the operating environment and the operating object, carry out certain real-time processing, and guide the robot to carry out operations. The second generation of robots has been widely used in industrial production.
Countries are currently researching the "intelligent robot", which not only has more than the second generation of robots with better environmental awareness, but also has a logical thinking, judgment and decision-making ability, according to the operational requirements and environmental information to work autonomously.
II. Application Scenarios of Industrial Robots
Since the early 1960s, mankind created the first industrial robots, robots show its great vitality, in just over 50 years, robotics technology has developed rapidly, in many manufacturing fields, industrial robots are most widely used in the field of automotive and automotive parts and components manufacturing industry, and is constantly expanding to other areas, such as machining industry, electronics, electrical industry, rubber and plastics industry, automobile and automotive parts and components manufacturing industry. Electrical industry, rubber and plastic industry, food industry, wood and furniture manufacturing and other fields. In industrial production, welding robots, grinding and polishing processing robots, welding robots, laser processing robots, spraying robots, handling robots, vacuum robots and other industrial robots have been adopted in large numbers. The following is an introduction to some of the application scenarios and technical characteristics of industrial robots.
III. The current situation of industrial robots
Along with the increasing rise of industrial robots, "machine for man" will become the trend. Foxconn has previously announced that it will purchase a million robots in three years, is expected to 2016 will be built in Shanxi Jincheng, "the world's largest intelligent robot production base".
Automotive, electronics, food, chemicals, plastics and rubber, metal products, six manufacturing industries, is seen as the current application of industrial robots in the main areas, the agency predicted that there will be 1 million to 2 million units of annual demand, accounting for China's industrial robots market demand of about 70%.
As of September this year, the whole of China's robotics enterprises has reached nearly 420. In addition, more than 30 robotics industrial parks are currently under construction across China.
The reason why industrial robots are surging in the Chinese market is, firstly, because in terms of cost, robots are usually only one-fourth of the cost of labor; secondly, robots can also bring a lot of new added value in terms of quality, efficiency and management. Therefore, in the rapid improvement of robotics technology, prices have fallen dramatically, labor shortages, rising labor costs and other factors, China's industrial robotics industry is in a blowout era.
IV. Key technologies of industrial robots
1. Robot basic system composition
Industrial robot consists of 3 major parts and 6 subsystems, which are mechanical part, sensing part and control part, and the 6 subsystems can be divided into mechanical structure system, drive system, sensing system, robot environment interaction system, human-machine interaction system and control system.
Industrial robot system composition
(1) The mechanical structure system of industrial robots consists of three major parts: the base, the arm, and the end manipulator, and each of these major parts has a number of mechanical systems with several degrees of freedom. If the base has a walking mechanism, it constitutes a walking robot; if the base does not have a walking and bending mechanism, it constitutes a single robot arm. The arm generally consists of an upper arm, a lower arm, and a wrist. The end manipulator is an important part directly mounted on the wrist, it can be two fingers or multi-finger hand grasp, can also be a paint spray gun, welding tools and other operating tools.
(2) drive system, in order to make the robot operation, need to be placed in the joints, that is, each degree of freedom of movement on the transmission device, which is the drive system. The drive system can be hydraulic, pneumatic, electric, or a combination of them to apply the integrated system, can be a direct drive or indirect drive through the synchronous belt, chain, wheel system, harmonic gears and other mechanical transmission mechanism.
(3) The sensing system consists of an internal sensor module and an external sensor module to obtain meaningful information about the state of the internal and external environment. The use of smart sensors improves the level of mobility, adaptability and intelligence of the robot. The human sensory system is extremely dexterous in sensing information about the external world, however, sensors are more effective than the human sensory system for some specific information.
(4) Robot environment exchange system is a modern industrial robot and the external environment of the equipment interchangeable contact and coordination system. Industrial robots and external equipment set into a functional unit, such as processing unit, welding unit, assembly unit, etc.. Of course, it can also be multiple robots, multiple machine tools or equipment, multiple parts storage devices, etc. into a functional unit to perform complex tasks.
(5) man-machine exchange system is the operator and the robot control and contact with the robot device, for example, the standard terminal of the computer, command console, information display board, danger signal alarm, etc.. The system is summarized into two main categories: command-giving devices and information display devices.
6) The robot control system is the brain of the robot and is the main factor in determining the function and performance of the robot.
The task of the control system is to control the robot's actuator to complete the prescribed movement and function according to the robot's operation instruction program and the signal back from the sensor. If the industrial robot does not have information feedback characteristics, it is an open-loop control system; if it has information feedback characteristics, it is a closed-loop control system. According to the control principle, the control system can be divided into program control system, adaptive control system and artificial intelligence control system. According to the form of control operation, the control system can be divided into point control and trajectory control. The point position type only controls the accurate positioning of the actuator from one point to another, and is suitable for operations such as loading and unloading of machine tools, spot welding and general handling, loading and unloading, etc. The continuous trajectory type controls the movement of the actuator according to a given trajectory, and is suitable for operations such as continuous welding and painting.
The task of the control system is to control the robot's actuator to complete the prescribed movement and function according to the robot's operation instruction program and the signal back from the sensor. If the industrial robot does not have information feedback characteristics, it is an open-loop control system; if it has information feedback characteristics, it is a closed-loop control system. According to the control principle, the control system can be divided into program control system, adaptive control system and artificial intelligence control system. According to the form of control operation, the control system can be divided into point control and trajectory control. A complete set of industrial robots includes robot body, system software, control cabinet, peripheral mechanical equipment, CCD vision, fixture/gripper, PLC control cabinet for peripheral equipment, and demonstrator/demonstrator box.
The following section focuses on the drive system and sensing system of the robot.
2. Robot drive system
The drive system of industrial robots is divided into three major categories, namely hydraulic, pneumatic and electric, according to the power source. According to the needs of these three basic types can also be combined into a composite drive system. These three types of basic drive systems have their own characteristics.
Hydraulic drive system: As hydraulic technology is a more mature technology. It has a large power, force (or moment) and inertia ratio, fast response, easy to realize the characteristics of direct drive. Suitable for use in these robots with large load carrying capacity, large inertia and working in a welding-proof environment. However, the hydraulic system requires energy conversion (electrical energy into hydraulic energy), speed control in most cases using throttling speed regulation, the efficiency is lower than the electric drive system. The hydraulic system's liquid sludge drain can pollute the environment, and the operating noise is also higher. Because of these weaknesses, in recent years, they are often replaced by electric systems in robots with loads of 100kg or less.
Fully hydraulic heavy-duty robots
Pneumatic drive has the advantages of fast speed, simple system structure, easy maintenance and low price. However, due to the low working pressure of the pneumatic device, it is not easy to accurately position, generally only used for industrial robot end-effector drive. Pneumatic hand gripping, rotary cylinder and pneumatic sucker as the end-effector can be used for medium and small load workpiece gripping and assembly. Pneumatic suction cups and pneumatic robot grippers are shown in the figure.
Pneumatic suction cups and pneumatic robot grippers
Motor drive is a mainstream drive mode of modern industrial robots, divided into four categories of motors: DC servo motors, AC servo motors, stepper motors and linear motors. DC servo motors and AC servo motors with closed-loop control, generally used for high-precision, high-speed robot drive; stepper motors for precision and speed requirements are not high occasions, the use of open-loop control; linear motors and their drive control systems have become technically mature, has a traditional transmission device can not be compared to the superior performance, such as adapting to the very high-speed and very low-speed applications, high acceleration, high accuracy, no empty return, low wear, structure and structure of the robot gripper. No empty back, low wear, simple structure, no reducer and gear screw coupling. In view of the large number of linear drive requirements in parallel robots, linear motors have been widely used in the field of parallel robots.
3. Robot Sensing System
Robot perception system transforms various internal state information and environmental information of the robot from signals into data and information that can be understood and applied by the robot itself or between robots. In addition to the need to perceive mechanical quantities related to its own working state, such as displacement, velocity, acceleration, force and torque, visual perception technology is an important aspect of industrial robot perception.
Visual servo systems use visual information as feedback signals for control to adjust the position and attitude of the robot. Applications in this area are mainly in the semiconductor and electronics industries. Machine vision systems are also widely used in various aspects of quality inspection, identification of workpieces, food sorting, and packaging.
Usually, the robot visual servo control is position-based visual servo or image-based visual servo, which are also known as 3D visual servo and 2D visual servo, respectively, and each of these two methods has its own advantages and applicability, as well as some shortcomings, so 2.5-dimensional visual servo methods have been proposed.
The position-based visual servo system utilizes the parameters of the camera to establish the mapping relationship between the image information and the position/attitude information of the robot end-effector to realize the closed-loop control of the robot end-effector position. The end-effector position and attitude errors are estimated from the end-effector position information extracted from the real-time captured images and the geometric model of the localized target, and then based on the position and attitude errors, the new position and attitude parameters of each joint are obtained. Position-based visual servoing requires that the end-effector should always be observable in the visual scene and its 3D positional attitude information is calculated. Elimination of disturbances and noise in the image is the key to ensure accurate calculation of position and attitude errors.
The 2D vision servo derives the error signal by comparing the features of the image captured by the camera with a given image (not the 3D geometric information). The robot is then corrected by the joint controller and vision controller and the current operating state of the robot, allowing the robot to complete servo control. Compared with 3D visual servoing, 2D visual servoing is more robust to the calibration errors of the camera and the robot, but problems such as the singularity of the image Jacobi matrix and the local minima are inevitably encountered in the design of the visual servo controller.
To address the limitations of 3D and 2D visual servo methods, F. Chaumette et al. proposed a 2.5-dimensional visual servo method. It decouples the closed-loop control of camera translation displacement and rotation, and reconstructs the orientation and imaging depth ratio of the object in 3D space based on the image feature points, with the translation part represented by the coordinates of the feature points on the image plane. This method can successfully combine the image signals and the position signals extracted based on the image organically, and synthesize the error signals generated by them for feedback, which largely solves the problems of robustness, singularity, and local minima. However, there are still some problems to be solved in this method, such as how to ensure that the reference object is always located within the camera field of view during the servoing process, and the existence of non-unique solutions when decomposing the singularity matrix.
When modeling the vision controller, a suitable model needs to be found to describe the mapping relationship between the robot's end-effector and the camera. The method of image Jacobi matrices is a widely used class of methods in the field of robot vision servoing research. The Jacobi matrix of an image is time-varying, so, it needs to be calculated or estimated online.
4. Key Basic Robot Components
There are 4 major components of a robot, 22% of the cost of the body, 24% of the servo system, 36% of the reducer and 12% of the controller. The key basic components of the robot refers to the composition of the robot drive system, control system and human-machine interaction system, play a key role in influencing the performance of the robot, and has the generality and modularity of the component unit. Robot key components are mainly divided into the following three parts: high-precision robot reducer, high-performance AC and DC servo motors and drives, high-performance robot controller.
1) Reducer
Reducer is a key component of the robot, and at present, two types of reducers are mainly used: harmonic gear reducer and RV reducer.
The harmonic transmission method was invented by American inventor C. WaltMusser in the mid-1950s. Harmonic gear reducer is mainly composed of wave generator, flexible gear and rigid gear 3 basic components, relying on the wave generator to make flexible gear to produce controlled elastic deformation, and with rigid gear meshing to transfer motion and power, single-stage transmission speed ratio up to 70 ~ 1000, with the help of flexible wheel deformation can be done in reverse without backlash meshing. Compared with the general reducer, when the output torque is the same, the volume of the harmonic gear reducer can be reduced by 2/3, the weight can be reduced by 1/2. flexible wheel to withstand a large alternating load, and thus its material fatigue strength, processing and heat treatment requirements are high, the manufacturing process is complex, the flexible wheel performance is the key to high-quality harmonic gear reducer.
The German LorenzBaraen proposed the principle of cycloid planetary gear transmission in 1926, and the Japanese TEIJINSEIKICo., Ltd. took the lead in developing the RV reducer in the 1980's. The RV reducer consists of the front stage of a planetary gearhead and the rear stage of a cycloid reducer. Compared to harmonic gearheads, RV gearheads offer better slewing accuracy and accuracy retention.
Chen Shixian invented the live gear transmission technology. The fourth generation of oscillatory roller transmission (ORT) has been successfully applied to many industrial products. Compound oscillatory roller transmission (CORT) proposed on the basis of ORT not only has the similar advantages of RV transmission, but also overcomes the shortcomings of the RV transmission crankshaft shaft bearing force, low life, and further improves the service life and load carrying capacity; CORT's structure allows it in the same The structure of CORT makes the return difference smaller under the same precision index, and the movement precision and rigidity higher, which alleviates the defects of RV transmission requiring high manufacturing precision, and can relatively reduce the processing requirements and manufacturing costs.CORT is independently developed in China, and owns independent intellectual property rights. Anshan Wear-resistant Alloy Research Institute and Zhejiang Hengfengtai Reducer Manufacturing Co., Ltd. have both successfully developed CORT reducers for robots.
ORT reducer CORT reducer
At present, in terms of high-precision robot reducer, 75% of the market share are monopolized by two Japanese reducer companies, respectively, to provide RV cycloid reducer Japan Nabtesco and provide high-performance harmonic reducer Japan Harmonic Drive. including ABB, FANUC, KUKA, MOTOMAN, including the international mainstream robot manufacturers, the reducer by the above two companies to provide, with the domestic and international robot manufacturers, the reducer by the above two companies. The gearboxes of international mainstream robot manufacturers, including ABB, FANUC, KUKA and MOTOMAN, are all provided by the above two companies. What is different from the general models chosen by domestic robotics companies is that the international mainstream robot manufacturers have signed a strategic cooperative relationship with the above two companies, and most of the products provided are specialized models improved according to the special requirements of the manufacturers on the basis of the general models. Domestic research in high-precision cycloid reducer started late, only in some colleges and universities, research institutes have had relevant research. At present, there are no mature products used in industrial robots. In recent years, some domestic manufacturers and institutions have begun to devote to the localization and industrialization of high-precision cycloid reducer research, such as Zhejiang Hengfengtai, Chongqing University State Key Laboratory of Mechanical Transmission, Tianjin Reducer Factory, Qinchuan Machine Tool Factory, Dalian Railway Institute and so on. In terms of harmonic reducer, there are alternative products in China, such as Beijing Sinotech Kemi, Beijing Harmonic Drive, but the corresponding products in the input speed, torsion height, transmission accuracy and efficiency with Japanese products there is still a small gap, the mature application of industrial robots has just begun.
2) Servo motors
In the servo motor and drive, the current European robot drive part is mainly provided by Lenze, Lust, Bosch Rexroth and other companies, these European motors and drive components overload capacity, dynamic response is good, the drive openness is strong, and has a bus interface, but the price is expensive. The Japanese brand industrial robot key components are mainly provided by Yaskawa, Panasonic, Mitsubishi and other companies, its price is relatively low, but the dynamic response is poor, openness is poor, and most of them only have analog and pulse control mode. In recent years, China has also carried out basic research and industrialization of high-power AC permanent magnet synchronous motors and drive parts, such as Harbin Institute of Technology, Beijing and Lisi, Guangzhou CNC and other units, and has a little bit of production capacity, but its dynamic performance, openness and reliability need to be verified by more practical robotics project applications.
3) Controller
In terms of robot controllers, the current mainstream foreign robot manufacturers are in the general multi-axis motion controller platform based on independent research and development. At present, the general multi-axis controller platform is mainly divided into embedded processors (DSP, POWER PC) as the core of the motion control card and industrial computer plus real-time system as the core of the PLC system, which are represented by Delta Tau's PMAC card and Beckhoff's TwinCAT system. Domestic in the motion control card, solid high company has developed the corresponding mature products, but in the application of the robot is relatively small.
5. Robot operating system
The common robot operating system (robot operating system, ROS) is a standardized construction platform designed for robots, which enables every robot designer to use the same operating system for robot software development.ROS will promote the development of the robot industry in the direction of hardware and software independence. The hardware-software independent development model has greatly contributed to the development and rapid advancement of PC, laptop and smartphone technologies.
ROS is more difficult to develop than a computer operating system. Computers only need to deal with some well-defined mathematical operations, while robots need to face more complex actual motion operations.
ROS provides standard operating system services, including hardware abstraction, underlying device control, implementation of common functions, inter-process messages, and packet management.
ROS is divided into two layers, the lower layer is the operating system layer, and the higher layer is the various software packages contributed by the user community to realize different functions of the robot.
The main existing robot operating system architectures are the linux-based Ubuntu open source operating system. In addition, various types of ROS systems have been developed at Stanford University, Massachusetts Institute of Technology, and the University of Munich in Germany. Microsoft's robotics development team also released a "Windows robotics version" in 2007.
6. Robot Motion Planning
In order to improve the efficiency of work, and so that the robot can complete a specific task in the shortest possible time, there must be a reasonable motion planning. Offline motion planning is divided into path planning and trajectory planning.
The goal of path planning is to make the distance between the path and the obstacle as far as possible while the length of the path is as short as possible; the purpose of trajectory planning is mainly to make the robot's joints in the spatial movement of the robot's running time is as short as possible, or the energy is as small as possible. Trajectory planning in the path planning based on the addition of time series information, the robot to perform the task of speed and acceleration planning, in order to meet the requirements of smoothness and speed controllability.
Demonstration reproduction is one of the methods to realize path planning, through the operation space for demonstration and recording the results of the demonstration, and reproduced in the work process, on-site demonstration directly corresponds to the robot needs to complete the action, the path is intuitive and clear. The disadvantage is that it requires experienced operators and consumes a lot of time, and the path may not be optimized. In order to solve the above problems, a virtual model of the robot can be built, and the path planning of the operation task can be accomplished through virtual visualization.
Path planning can be carried out in the joint space.Gasparetto uses five times B-splines as the interpolation function for the joint trajectories, and the integral of the square of the added acceleration with respect to the motion time is used as the objective function for optimization to ensure that the motion of each joint is smooth enough. Songguo Liu calculates the interpolation of the robot's joint trajectories by using five times B spline, and the velocity and acceleration endpoint values of the robot's individual joints can be configured arbitrarily according to the smoothness requirements. In addition, trajectory planning in the joint space can avoid the singularity problem in the operation space.Huo et al. designed a joint trajectory optimization algorithm for avoiding singularity in the joint space by using the redundancy in the functionality of a certain joint of a 6-degree-of-freedom arc welding robot during a task, and taking the robot's singularity and joint limitations as the constraints to optimize the computation by using the TWA method.
The joint space path planning has the following advantages compared with the operation space path planning:
① Avoiding the singularity problem of the robot in the operation space;
② Since the motion of the robot is controlled by controlling the motion of the joint motors, a large number of forward and inverse kinematics calculations are avoided in the joint space;
③The individual joint trajectories in the joint space facilitate the optimization of the control.
V. Classification of industrial robots
1. From the point of view of mechanical structure, it is divided into series and parallel robots.
(1) series robot is characterized by the movement of one axis will change the origin of the coordinates of the other axis, in the position solution, the series robot is easy to solve the positive solution, but the reverse solution is very difficult;
(2) The parallel robot uses a parallel mechanism, and the motion of one axis does not change the coordinate origin of the other axis. The parallel robot has the advantages of large stiffness, stable structure, large load carrying capacity, high precision of micro-motion and small motion load. Its positive solution is difficult to inverse solution is very easy. Series and parallel robots are shown in the figure.
Tandem robot, parallel robot
2. Industrial robots are divided into the following categories according to the form of the operator's coordinates: (The form of the coordinates refers to the form of the reference coordinate system taken by the operator's arm in motion.)
(1) Cartesian coordinate type industrial robots
Its motion part consists of three mutually perpendicular linear movements (i.e., PPP), and its workspace figure is rectangular. Its moving distance in each axial direction can be read out directly on each coordinate axis, which is intuitive, easy to program and calculate the position and attitude, high positioning accuracy, coupling-free control, simple structure, but the space occupied by the body is large in volume, small action range, poor flexibility, and difficult to work in coordination with other industrial robots.
(2) Cylindrical coordinate type industrial robot
The form of motion is realized by a rotation and two mobile motion system, the workspace graph for the cylinder, compared with the Cartesian Coordinate Industrial Robot, under the same conditions of the workspace, the body occupies a small volume, but the range of motion is large, its positional accuracy is second only to Cartesian Coordinate Robot, difficult to coordinate with other industrial robots.
(3) Ball coordinate industrial robot
Ball-coordinate industrial robot, also known as polar-coordinate industrial robot, its arm movement by two rotating and a linear movement (i.e., RRP, a rotary, a pitch and a retractable movement) composed of a sphere in the workspace, it can be up and down pitching action and can grasp the ground or teach the coordination of low position of the workpiece, its positional accuracy is high, the positional error and the length of the arm is proportional to the length of the arm.
4)Multi-articulated industrial robots
Also known as rotary coordinate industrial robots, this industrial robot arm and human upper limb similar to the first three joints are rotary vice (i.e., RRR), the industrial robot is generally composed of columns and large and small arms, the columns and the big arm see the formation of shoulder joints, the big arm and the elbow joints between the small arm, so that the big arm to do rotary motion and pitch swing, the small arm to do the pitch swing. Its structure is the most compact, flexibility, smallest footprint, can work in coordination with other industrial robots, but the positional accuracy teach low, there is a balance problem, control coupling, this industrial robot is more and more widely used.
(5) Plane joint type industrial robot
It uses a mobile joint and two rotary joints (i.e., PRR), mobile joints to achieve up and down movement, while the two rotary joints control the front and back, left and right movements. This form of industrial robot is also known as (SCARA (Seletive Compliance Assembly Robot Arm) assembly robot. In the horizontal direction, it has flexibility, while in the vertical direction, it has taught great rigidity. It is a simple structure, flexible action, mostly used in assembly operations, especially suitable for small-size parts insertion assembly, such as in the electronics industry, insertion, assembly in a wide range of applications.
3. Industrial robots according to the program input method to distinguish between two types of programming input type and teaching input type:
(1) Programming input type is the computer has been programmed on the operating program file, through the RS232 serial port or Ethernet and other communication methods to the robot control cabinet.
(2) There are two types of teaching methods for the Teach-In type: Teaching box teaching and direct operator-led actuator teaching.
Teaching box teaching by the operator with a manual controller (teaching box), the command signal to the drive system, so that the actuator in accordance with the required sequence of action and the trajectory of the exercise once. The use of teaching box for teaching industrial robots is relatively common, the general industrial robots are equipped with teaching box teaching function, but for the complex trajectory of the situation, teaching box teaching can not achieve the desired results, such as for complex surfaces of the paint spraying work of the painting robot.
Robot Teaching Box
When the operator leads the actuator directly, the robot is taught to perform the required sequence of movements and trajectory. In the teaching process at the same time, the work program information is automatically stored in the program memory in the robot automatically work, the control system from the program memory to detect the corresponding information, the command signal to the drive mechanism, so that the actuator to reproduce the teaching of a variety of actions.
Ⅵ. industrial robot performance evaluation index
The basic parameters and performance indicators of robot characteristics mainly include workspace, degrees of freedom, payload, motion accuracy, motion characteristics, dynamic characteristics.
Industrial robot performance judgment indicators
1. Work space (Work space) refers to the specific part of the robot arm in certain conditions can reach the space position collection. The traits and size of the workspace reflect the size of the robot's working capacity. When understanding the work space of a robot, the following points should be noted:
(1) Usually the workspace indicated in the manual of industrial robots refers to the range that the origin of the coordinate system of the mechanical interface on the wrist can reach in space, that is, the range that the center point of the flange at the end of the wrist can reach in space, rather than the range that can be reached by the endpoint of the end-effector. Therefore, when designing and selecting the robot, it is important to pay attention to the working space that the robot can actually reach after installing the end-effector.
(2) The working space provided in the robot manual is often smaller than the maximum space in the kinematic sense. This is because in the reachable space, the arm position is different while the payload, the maximum speed and maximum acceleration are not the same, in the arm pole maximum position allows the limit value is usually smaller than other positions. In addition, there may be degradation of degrees of freedom at the boundary of the robot's maximum reachable space, which is called the singular bit pattern, and the evolution of degrees of freedom occurs in a considerable range around the singular bit pattern, and this part of the workspace can not be utilized when the robot is working.
(3) In addition to the edge of the workspace, industrial robots in practical applications may also be limited by the mechanical structure of the workspace, there also exists an area inside the workspace that cannot be reached by the end of the arm, which is often referred to as the hollow or cavity. Cavity is a completely closed space within the workspace that cannot be reached by the end of the arm. And the cavity is along the shaft around the entire length of the arm can not reach the space.
2. Motion degrees of freedom refers to the number of variables required for the robot operator to move in space, used to indicate the degree of flexibility of the robot action parameter, generally to move along the axis and rotate around the axis of the number of independent movement to indicate.
A free object has six degrees of freedom in space (three degrees of freedom for rotation and three degrees of freedom for movement). Industrial robots are often open linkage systems with only one degree of freedom per joint kinematics, so usually the number of degrees of freedom of a robot is equal to its number of joints. The more degrees of freedom a robot has, the more powerful it is. A few days ago, industrial robots usually had 4-6 degrees of freedom. Redundant degrees of freedom occur when the number of joints (degrees of freedom) of a robot increases to the point where it is no longer useful for end-effector orientation and localization. The presence of redundant degrees of freedom increases the flexibility of the robot's work, but also makes control more complex.
Industrial robots can always be divided into two kinds of linear motion (abbreviated as P) and rotary motion (abbreviated as R) in terms of motion, and the application of the shorthand symbols P and R can indicate the characteristics of the degrees of freedom of motion of the manipulator, for example, RPRR indicates that the robot manipulator has four degrees of freedom, and that the joints move in the order of rotary-linear-rotary-rotary, starting from the base to the end of the arm. In addition, the degrees of freedom of motion of industrial robots have the limitations of the range of motion.
3. Payload
Payload refers to the weight of the object that the robot operator may carry at the end of the arm or the force or moment that it can withstand during operation, and is used to indicate the load capacity of the operator.
Robot in different positions, the maximum allowable mass is different, so the rated mass of the robot is the arm in any position in the workspace of the wrist joint end can handle the maximum mass.
4. Motion Accuracy
The accuracy of the robot mechanical system mainly involves position accuracy, repeat position accuracy, trajectory accuracy, repeat trajectory accuracy and so on.
Accuracy of position refers to the deviation between the commanded position and the actual position center when approaching the commanded position from the same direction. Repeat position accuracy refers to the degree of inconsistency of the actual position after responding to the same command position from the same direction for n times.
Trajectory accuracy is the degree of proximity of the robot mechanical interface to the commanded trajectory from the same direction n times. Trajectory repeatability refers to the degree of inconsistency between a given trajectory and the actual trajectory after following it n times in the same direction.
5. Motion characteristics (Sped)
Speed and acceleration are the main indicators of the robot's motion characteristics. In the robot manual, usually provides the maximum stabilized speed of the main degrees of freedom of motion, but in practice, simply consider the maximum stabilized speed is not enough, should also pay attention to its maximum permissible acceleration.
6. Dynamic characteristics of the structure dynamic parameters mainly include mass, moment of inertia, stiffness, damping coefficient, intrinsic frequency and vibration modes.
The design should minimize the mass and inertia. For the stiffness of the robot, if the stiffness is poor, the positional accuracy of the robot and the intrinsic frequency of the system will be decreased, which will lead to the dynamic instability of the system; however, for some operations (e.g., assembly operations), it is advantageous to appropriately increase flexibility, and ideally, it is desired to have the stiffness of the robot's arm bar adjustable. Increasing the damping of the system is advantageous for reducing the decay time of the oscillations and improving the dynamic stability of the system. Increasing the intrinsic frequency of the system to avoid the operating frequency range is also beneficial to improve the stability of the system.
Ⅶ. industrial robots face technical challenges
1, the robot market accounted for ninety percent of foreign capital
Robotics market is thriving, but China's robotics industry is not optimistic. According to market statistics, mainland China's industrial robotics market is monopolized by foreign manufacturers, Japanese brand manufacturers accounted for 52%, European manufacturers accounted for 30%, the remaining about 10% of mainland China manufacturers.
As the robotics industry entry threshold is quite high, so the global robotics market rankings of the top four vendors were Japan Fanuc, Yaskawa Electric, ABB and KUKA, a total of 50% of the market share.
On the other hand, in the next 30 years, mainland China's industrial robotics market will maintain at least 30% of the rapid growth. To this end, the global brand robotics manufacturers actively expand the scale of robot business sales in the Chinese mainland market, including FANUC, YASKAWA Electric, ABB and KUKA, etc. are actively in the Chinese mainland, set up factories.
At present, mainland China's industrial robots, although the industrialization of some initial progress, but due to the accuracy, speed and other aspects of foreign manufacturers than similar products, resulting in the industrialization of these products to a low degree of application, the market share is very small; some of the products of the technological level of foreign countries is only equivalent to the level of the middle of the 90s of the last century.
Li Xiaojia, director of the China Robot Industry Alliance Data Statistics Center, said that in 2013, China purchased and assembled nearly 37,000 industrial robots, of which foreign-funded robots are generally 6-axis or more high-end industrial robots, almost monopolizing the automotive manufacturing, welding and other high-end industry sectors, accounting for 96%. The main application of domestic robots is still mainly handling and loading and unloading robots, in the low-end areas of the industry.
It is worth noting that the current development of China's robotics industry with foreign countries, the gap between the risk of being further widened. At present, China's robotics industry in general is still in its infancy, the lack of brand recognition of industrial robots, the largest robotics companies annual production of robots only a few thousand units. With foreign robotics companies have China as a production base, the development of independent brands of industrial robots will be further compressed.
At the same time, due to the key core components subject to others, the risk of industrial hollowing out expanded. The three key components of industrial robots (motors and servers, gearboxes, control systems) are mainly sourced from abroad, and mainland Chinese manufacturers relatively lack competitive R&D and manufacturing capabilities, and have long relied on imports. As the upstream of the industrial chain is not supported by core component manufacturers, it will be subject to long-term constraints.
2, industrial robots face technical challenges
We need to soberly see the huge challenges facing the development of China's industrial robotics industry.
First of all, the robot's top-level architectural design and basic technology is controlled by developed countries, in the robot cost structure of a larger proportion of reducers, servo motors, controllers, CNC systems are heavily reliant on imports, domestic robots do not have a significant cost advantage.
Secondly, there is the risk of low-end locking. On the one hand, developed countries will not easily to China to transfer or authorize the core robotics technology, patents, China's robotics enterprises through participation in the development of international standards, technology cooperation and research and development to enter the middle and high-end market impediments; on the other hand, the local government's blind investment in the industry may form a surplus of production capacity, resulting in duplication of construction and low-priced competition.
Again, there is a lack of effective connection between robot R&D, manufacturing and application. Robot-related technology research and development of leading universities and institutes do not have the ability to develop the market, and enterprises in the basic R & D investment is still very low, the domestic combination of industry, academia and research and the existence of a number of institutional barriers, resulting in R & D and manufacturing link disconnect.
Foreign monopoly of the domestic market for the status quo, experts suggest that through a variety of ways to seek a "breakthrough" and catch up: first of all, we must strengthen the tracking of international robotics research, the development and introduction of the actual development of China's "Robotics Roadmap", clear steps for technological development, focus on breakthroughs, and the development of the robotics roadmap, the development of the robotics roadmap. Clearly the steps of technological development, key breakthroughs in key core technologies, processes and components, as well as industrialization path.
Secondly, we need to establish a robot development model in line with China's actual development. Strengthen the integrated application of industry segments, strengthen the combination of industry, academia, research and use of collective research, focusing on breakthroughs in key core components, as soon as possible to form a robot body, key components, system integrators and other robotics industry chain to promote the whole.
In addition, it is necessary to accelerate the cultivation of leading industrial robot enterprises and brands. China should cultivate and develop its own brand of industrial robots as an important task to create an upgraded version of China's economy. The introduction of industrial robot industry directory, collaborative promotion to carry out the localization of industrial robots.