I. Classification of industrial robots
According to the operator coordinate form can be divided into:
(1) Cartesian coordinate type industrial robots
Its motion part consists of three mutually perpendicular linear movements (i.e. PPP), and its workspace graph 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, control without coupling, simple structure, but the space occupied by the body is large in size, the action range is small, 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, in the same workspace conditions, the body occupies a small volume, but the range of motion is large, its positional accuracy is second only to the Cartesian Coordinate robot, difficult to work in coordination with other industrial robots.
(3) Spherical Coordinate Robot
Also known as polar coordinate industrial robot, its arm movement by two rotation and a linear movement (i.e., RRP, a rotary, a pitch and a telescopic movement) composed of the workspace for a sphere, it can be up and down pitch action and can grasp the ground or teach the low position of the coordination of the workpiece, its positional accuracy is high, the positional error is proportional to the arm length.
(4) Multi-joint 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, columns and large arms see the formation of the shoulder joints, large arms and small arms to form elbow joints, can make the large arm to do rotary motion and pitch swing, 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 rear, 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.
According to the driving method can be divided into:
(1) pneumatic industrial robots
This type of industrial robots to compressed air to drive the operator, the advantages of the air source is convenient, rapid action, simple structure and low cost, no pollution, the disadvantage is that the air is compressible, resulting in poor stability of the working speed, but also because of the gas source pressure is generally only about 6kPa, so this type of industrial robots grasp force is smaller, generally only a few tens of Newtons, the maximum of more than a hundred Newtons.
(2) Hydraulic industrial robots
Hydraulic pressure is much higher than air pressure, generally about 70kPa, so the hydraulic drive industrial robot has a larger lifting capacity, up to thousands of Newtons. These industrial robots are compact, smooth transmission, sensitive action, but the sealing requirements are high, and should not work in high or low temperature environment.
(3) Electric industrial robots
This is currently the most used class of industrial robots, not only because of the many varieties of electric motors, industrial robot design provides a variety of options, but also because they can use a variety of flexible control methods. In the early days, stepper motors were used to drive them, then DC servo drive units were developed, and now AC servo drive units are also developing rapidly. These drive units either drive the operator directly, or through devices such as harmonic reducer to slow down the drive, the structure is very compact and simple.
II. industrial robot control system
Industrial robot control technology
- Is developed on the basis of the control technology of traditional mechanical systems, so there is no fundamental difference between the two but the industrial robot control system has many special features. The characteristics are as follows:
- Industrial robots have a number of joints, typical industrial robots have five or six joints, each joint is controlled by a servo system, the movement of multiple joints requires each servo system to work together.
- Industrial robot's work task is to require the operator's hand to carry out spatial point movement or continuous trajectory movement, the motion control of industrial robots, the need for complex coordinate transformation operations, as well as the inverse operation of the matrix function.
- The mathematical model of industrial robots is a multivariate, nonlinear and variable parameter complex model, there is also coupling between the variables, so the control of industrial robots is often used in the control of feed-forward, compensation, decoupling and adaptive and other complex control techniques.
- The more advanced industrial robots require the determination and analysis of environmental conditions, control instructions, the use of computers to establish a huge information base, the use of artificial intelligence for control, decision-making, management and operation, in accordance with the given requirements, the automatic selection of the best control law.
The control system of industrial robots sends out basic requirements:
- Realize the position, speed, acceleration and other control functions of industrial robots, for continuous trajectory movement of industrial robots must also have the trajectory of the planning and control functions.
- Convenient human-machine interaction function, the operator uses the direct command code to the industrial robot role instructions. The use of industrial robots with operational knowledge of the memory, correction and work program jump function.
- It has the function of detecting and feeling the external environment (including operating conditions). In order for the industrial robot to have the ability to adapt to changes in the external state, the industrial robot should be able to measure, recognize, judge, and understand functions such as vision, force sense, tactile sense, and other relevant information. In automated production lines, industrial robots apply the ability to exchange information with other equipment and coordinate their work.
Classification of industrial robot control system:
- Industrial robot control system can be classified from different perspectives, such as controlling the movement in different ways, which can be divided into joint control, Cartesian space motion control and adaptive control; according to the different ways of trajectory control, which can be divided into point control and continuous trajectory control; according to the different ways of speed control, which can be divided into speed control, acceleration control, force control.
- Program control system, to each degree of freedom to impose a certain regular control role, the robot can realize the required spatial trajectory.
- Adaptive control system, when the external conditions change, in order to ensure the required quality or in order to improve the quality of control by itself with the accumulation of experience, the process is based on the state of the operating machine and servo error observation, and then adjust the parameters of the nonlinear model, until the error disappears. The structure and parameters of such a system can change automatically over time and conditions.
- Artificial intelligence systems, which cannot prepare a motion program in advance, instead require that the control action be determined in real time during the motion process based on the surrounding state information obtained. When the external conditions change, in order to ensure the required quality or in order to improve the control quality by itself with the accumulation of experience, the process is based on the observation of the state of the operating machine and the servo error, and then adjust the parameters of the nonlinear model until the error disappears. The structure and parameters of such a system can change automatically with time and conditions. Thus this system is an adaptive control system.