Understand the structure, drive and technical indicators of industrial robots in one article

Common kinematic configurations

1. Cartesian manipulator advantages: It is easy to achieve through computer control and high precision. Disadvantages: It hinders work, occupies a large area, has low movement speed and poor sealing.

① Welding, handling, loading and unloading, packaging, stacking, depalletizing, flaw detection, classification, assembly, labeling, coding, (soft profiling) spraying, target following, bomb disposal and other work.

② It is particularly suitable for flexible operations with multiple varieties and batches, and plays a very important role in stabilizing and improving product quality, increasing labor productivity, improving working conditions and rapid product renewal.

2. Articulated operating arm (joint type)

The joints of the joints are all rotating, similar to the most common structure in the human arm. Its working range is relatively complex.

① Rapid testing and product development of auto parts, molds, sheet metal parts, plastic products, sports equipment, glass products, ceramics, aviation, etc. ② Three-coordinate measurement and error detection for manufacturing quality control such as body assembly and general assembly. ③ Rapid prototyping of antiques, artworks, sculptures, cartoon character modeling, portrait products, etc. ④ On-site measurement and testing of complete vehicles. ⑤ Human body shape measurement, production of medical equipment such as bones, human body shape production, medical cosmetic surgery, etc.

3. SCARA manipulator

SCARA机器人常用于装配作业, 最显著的特点是它们在x-y平面上的运动具有较大的柔性, 而沿z轴具有很强的刚性, 所以, 它具有选择性的柔性。这种机器人在装配作业中获得了较好的应用。

① Used extensively for assembling printed circuit boards and components ② Moving and placing objects, such as boards, etc. ③ Widely used in plastics, automotive industry, electronics industry, pharmaceutical industry and food industry. ④ Moving parts and assembly work.

4. Spherical coordinate manipulator

Features: The working range near the center bracket is large, the two rotating drive devices are easy to seal, and the covered working space is large. However, the coordinates are complex and difficult to control, and there is a sealing problem with the linear drive device.

5. Cylindrical coordinate manipulator

Advantages: Simple calculation; The linear part can be driven by hydraulic pressure, which can output greater power; It can be inserted into the cavity machine. Disadvantages: The space that its arm can reach is limited, and it cannot reach the space near the column or the ground; The linear drive part is difficult to seal and dustproof; When the rear arm is working, the rear end of the arm will touch other objects within the working range.

6. Redundant institutions

Usually, six degrees of freedom are required for spatial positioning. Using additional joints can help the mechanism avoid singular configurations. The following figure shows the configuration of a 7-degree-of-freedom manipulator.

7. Closed-loop structure

The closed-loop structure can improve the rigidity of the mechanism, but it will reduce the range of joint movement and the working space. ① Movement device; ② Parallel machine tool; ③ Micro-manipulation robot; ④ Force; ⑤ Cell manipulation robot in biomedical engineering, which can realize cell injection and segmentation; ⑥ Micro-surgical robot; ⑦ Attitude adjustment device of large radio telescope; ⑧ Hybrid equipment, such as SMT's Tricept hybrid manipulator module, which is a successful example of modular design based on parallel mechanism unit.

Several common structural forms of industrial robots (picture)

Main technical parameters of the robot

The technical parameters of a robot reflect the work that the robot can do and its highest operational performance, which are issues that must be considered when designing and applying robots. The main technical parameters of a robot include degrees of freedom, resolution, workspace, working speed, and workload.

1. Degrees of Freedom

The number of independent coordinate axis motions that a robot has. The degrees of freedom of a robot refer to the number of independent motion parameters required to determine the position and posture of the robot's hand in space. The opening and closing of the fingers, as well as the degrees of freedom of the finger joints are generally not included. The number of degrees of freedom of a robot is generally equal to the number of joints. The number of degrees of freedom commonly used by robots generally does not exceed 5 to 6.

2. Joint

That is, the kinematic pair, which is the mechanism that allows relative movement between the various parts of the robot arm.

3. Workspace

The total space that can be reached by the robot arm or hand mounting point. Its shape depends on the number of degrees of freedom of the robot and the type and configuration of each motion joint. The robot's workspace is usually described by two methods: graphical method and analytical method.

Method to express.

4. Working speed

The distance moved or angle rotated by the center of the mechanical interface or the center of the tool per unit time when the robot is in constant motion under working load conditions.

5. Workload

Refers to the maximum load that a robot can bear at any position within its working range, generally expressed in terms of mass, torque, and moment of inertia. It is also related to the running speed and the magnitude and direction of acceleration. Generally, the weight of the workpiece that can be grasped during high-speed operation is specified as the load-bearing capacity indicator.

6. Resolution

The minimum movement distance or minimum rotation angle that can be achieved.

7. Accuracy

Repeatability or repeatability: refers to the degree of difference when a robot repeatedly reaches a certain target position. Or the dispersion of the robot's position when it repeats several times in a row under the same position instruction. It is a measure of the density of a series of error values, that is, repeatability.

Common materials for robots

1) Carbon structural steel and alloy structural steel have good strength, especially alloy structural steel, whose strength is increased by 4 to 5 times, elastic modulus E is large, and deformation resistance is strong, so it is the most widely used material.

2) Aluminum, aluminum alloys and other light alloy materials have the common characteristics of light weight and low elastic modulus E, but the material density is small, so the E/ρ ratio is still comparable to that of steel. The quality of some rare aluminum alloys has been significantly improved. For example, the aluminum alloy with 3.2% (weight percentage) lithium added has an elastic modulus increased by 14% and an E/ρ ratio increased by 16%.

3) Fiber-reinforced alloys: Such alloys as boron fiber-reinforced aluminum alloys and graphite fiber-reinforced magnesium alloys have E/ρ ratios of 11.4×107 and 8.9×107, respectively. This fiber-reinforced metal material has a very high E/ρ ratio, but is expensive.

4) Ceramics Ceramic materials have good quality, but are brittle and difficult to process. Japan has trial-produced ceramic robot arm samples for use in small high-precision robots.

5) Fiber-reinforced composites have an excellent E/ρ ratio and a very outstanding advantage of large damping. Traditional metal materials cannot have such large damping, so there are more and more examples of using composite materials in high-speed robots.

6) Viscoelastic high damping materials Increasing the damping of robot links is an effective way to improve the dynamic characteristics of robots. There are many methods to increase the damping of structural materials. One of the most suitable methods for robots is to use viscoelastic high damping materials to perform constrained layer damping on the original components.

Main structure of the robot

1. Robot drive device

Concept: To make the robot run, a transmission device must be installed for each joint, that is, each degree of freedom of movement. Function: Provide the motive force for the movement of each part and joint of the robot.

Drive system: It can be hydraulic drive, pneumatic drive, electric drive, or a comprehensive system that combines them; it can be directly driven or indirectly driven through mechanical transmission mechanisms such as synchronous belts, chains, gear trains, harmonic gears, etc.

1. Electric drive device

Electric drive devices have simple energy, wide speed range, high efficiency, and high speed and position accuracy. However, they are often connected to a reduction gear, making direct drive difficult.

Electric drive devices can be divided into direct current (DC), alternating current (AC) and drive. DC servo brushes are easy to wear and form sparks. Brushless DC motors are also increasingly widely used. Stepper motor drives are mostly open-loop control, which is simple to control but not very powerful, and are mostly used in low-precision, low-power robot systems.

Before starting the electric motor, make the following checks:

1) Is the voltage appropriate (overvoltage may damage the drive module); the +/- polarity of the DC input must not be connected incorrectly, and the motor model or setting value on the drive controller is appropriate (not too large at the beginning); 2) The control line is connected securely, and it is best to consider shielding issues at industrial sites (such as using twisted pair cables); 3) Do not connect all the wires that need to be connected at the beginning, only connect the most basic system, and then gradually connect after it runs well. 4) Be sure to understand the grounding method, or use floating without connection. 5) Closely observe the status of the motor within half an hour of starting operation, such as whether the movement is normal, the sound and temperature rise, and stop and adjust immediately if any problems are found.