Industrial robot's internal structure
First, the robot drive device
Concept: To make the robot run, it is necessary to set the actuator for each joint, that is, for each degree of freedom of movement: to provide the motive force for each part of the robot and each joint.
Drive system: It can be hydraulic drive, pneumatic drive, electric drive, or an integrated system that combines them; it can be driven directly or indirectly driven by mechanical transmission mechanisms such as timing belts, chains, gear trains, harmonic gears, etc.
1, electric drive device
The electric drive has a simple energy source, a wide range of speed variations, high efficiency, and high speed and position accuracy. However, they are often associated with deceleration devices and direct drive is difficult.
Electric drive can be divided into direct current (DC), alternating current (AC) servo motor drive and stepper motor drive. DC servo motor brush is easy to wear, and easy to form sparks. Brushless DC motors have also been used more and more widely. Stepper motor drive is mostly open-loop control, simple control but low power, mostly used in low-precision low-power robot systems.
Fourth, the robot sensing system
1. The sensory system consists of an internal sensor module and an external sensor module to obtain meaningful information in internal and external environmental conditions.
2. The use of smart sensors improves the maneuverability, adaptability, and intelligence of the robot.
3, the use of smart sensors to improve the robot's mobility, adaptability and intelligent standards.
4. For some special information, sensors are more effective than human sensory systems.
V. Robot position detection
Rotary optical encoders are the most commonly used position feedback devices. Photodetectors convert light pulses into binary waveforms. The rotation angle of the shaft is obtained by calculating the number of pulses and the direction of rotation is determined by the relative phase of the two square wave signals.
The inductive synchronizer outputs two analog signals - the sine and cosine signals of the shaft angle. The rotation angle of the shaft is calculated from the relative amplitudes of these two signals. Inductive synchronizers are generally more reliable than encoders, but their resolution is lower.
Potentiometers are the most direct form of position detection. It is connected in a bridge and can generate a voltage signal proportional to the angle of rotation of the shaft. However, due to low resolution, poor linearity and sensitivity to noise.
The tachometer can output an analog signal that is proportional to the speed of the shaft. If there is no such speed sensor, the speed feedback signal can be obtained by the difference of the detected position with respect to time.
Sixth, robot force detection
Force sensors are usually mounted on the operating arm in the following three positions:
1, installed in the joint drive. The torque or force output of the driver/reducer itself can be measured. However, the contact force between the end effector and the environment cannot be well detected.
2. Mounted between the end effector and the end joint of the operating arm, it can be called a wrist force sensor. Typically, three to six force/torque components applied to the end effector can be measured.
3, installed in the "fingertip" of the end effector. Usually, these forces feel that the strain gauge is built into the finger and can measure one to four force components acting on the fingertip.
VII. Robot-environment interaction system
1. The robot-environment interaction system is a system that realizes the interconnection and coordination between industrial robots and devices in the external environment.
2. Industrial robots and external devices are integrated into one functional unit, such as processing and manufacturing units, welding units, and assembly units. It can also be integrated with multiple robots, multiple machine tools or devices, multiple parts storage devices, and the like.
3, it can also be multiple robots, multiple machine tools or equipment, multiple parts storage devices integrated as a functional unit to perform complex tasks.
Eight, human-computer interaction system
The human-computer interaction system is a device that allows an operator to participate in robot control and contact the robot. The system can be divided into two categories: instruction given device and information display device.
Check the following before powering on the motor:
1) The power supply voltage is appropriate (overvoltage may cause damage to the drive module); The +/- polarity of the DC input must not be connected incorrectly, the motor model or current setpoint on the drive controller is appropriate (do not start Too big)
2) The control signal lines are connected securely, and it is best to consider the shielding problem in the industrial field (such as using twisted pair);
3) Don't start with all the wires you need to connect, just connect to the most basic system. After it works well, connect it gradually.
4) Be sure to find out the grounding method, or use floating air.
5) During the first half hour of operation, the status of the motor should be closely observed, such as whether the movement is normal, sound and temperature rise, and the problem is immediately shut down for adjustment.
2, hydraulic drive
It is accomplished by a high-precision cylinder and piston, and linear motion is achieved by the relative motion of the cylinder and the piston rod.
Advantages: Large power, can save the deceleration device directly connected to the driven rod, compact structure, good rigidity, fast response, servo drive with high accuracy.
Disadvantages: The need for additional hydraulic source, easy to produce liquid leakage, not suitable for high and low temperature applications, so the hydraulic drive is currently used in extra large power robot systems.
Select the appropriate hydraulic oil. Prevents the mixing of solid impurities into the hydraulic system and prevents air and water from invading the hydraulic system. Mechanical operations should be gentle and smooth mechanical operations should avoid rough, otherwise it will inevitably produce impact load, so that frequent mechanical failure, greatly reducing the service life. Pay attention to cavitation and overflow noise. Always pay attention to the sound of the hydraulic pump and relief valve during operation. If the hydraulic pump has “cavitation” noise, it cannot be eliminated after being exhausted. It should be found out after troubleshooting. Keep an appropriate oil temperature. The working temperature of the hydraulic system is generally controlled between 30 ~ 80 °C.
3, pneumatic drive
The pneumatically driven structure is simple, clean, sensitive, and has a cushioning effect. However, compared with the hydraulic drive device, the power is small, the rigidity is poor, the noise is large, and the speed is not easy to control. Therefore, it is mostly used for a point-controlled robot with low precision.
(1) It has the characteristics of high speed, simple system structure, convenient maintenance and low price. Suitable for use in medium- and low-load robots. However, due to the difficulty in achieving servo control, many robots are used in program control, such as in the upper and lower materials and stamping robots.
(2) In most cases it is used in small and medium robots that implement two-position or finite-point control.
(3) Most control devices currently use programmable controllers (PLC controllers). Pneumatic logic components can be used to control devices in flammable and explosive environments.
Second, the linear transmission mechanism
The transmission is a key part of connecting the power source and the moving link. According to the joint form, the commonly used transmission mechanism is a linear transmission and a rotary transmission mechanism.
The linear transmission method can be used for the X, Y, Z-direction driving of the Cartesian coordinate robot, the radial driving and vertical lifting driving of the cylindrical coordinate structure, and the radial telescopic driving of the spherical coordinate structure.
Linear motion can be converted into linear motion through gears, racks, nuts, and other transmission elements. It can also be driven by a linear drive motor, or it can be generated directly by the piston of a cylinder or a hydraulic cylinder.
1, gear rack device
The rack is usually fixed. The rotational motion of the gear is converted into the linear motion of the pallet.
Advantages: simple structure.
Disadvantages: Large difference in return.
2, ball screw
The ball is embedded in the spiral groove of the screw and nut, and the ball can continuously circulate through the guide groove in the nut.
Advantages: Small friction, high transmission efficiency, no creep, high precision
Disadvantages: high manufacturing costs and complex structures.
Self-locking problem: In theory, the ball screw can also be self-locking, but the actual application does not use this self-locking, mainly because: poor reliability, or high processing costs; because the diameter and lead ratio is very large, In general, a self-locking device such as a worm gear is added.
Third, rotating transmission mechanism
The purpose of using a rotary transmission mechanism is to convert the higher speed output from the drive source of the motor into a lower speed and obtain a larger torque. The most frequently used rotary transmission mechanisms in robots are gear trains, timing belts, and harmonic gears.
1, gear chain
(1) Speed relationship
(2) Torque relationship
2, timing belt
The timing belt is a belt with many types of teeth that meshes with a timing belt pulley that also has gear teeth. When working, it is equivalent to a soft gear.
Advantages: no sliding, good flexibility, low price, high repeatability of positioning.
Disadvantages: Has a certain degree of elastic deformation.
3, harmonic gear
The harmonic gear consists of three main parts: a rigid gear, a harmonic generator and a flexible gear. The rigid gear is generally fixed, and the harmonic generator drives the flexible gear to rotate.
main feature:
(1) Large transmission ratio, 50-300 for single stage.
(2) Smooth transmission and high bearing capacity.
(3), high transmission efficiency, up to 70% -90%.
(4), high transmission accuracy, 3-4 times higher than the ordinary gear transmission.
(5) The return difference is small and can be less than 3'.
(6) No intermediate output can be obtained, and the flex-wheel stiffness is low.
Harmonic transmission devices have been widely used in countries with advanced robot technology. For Japan alone, 60% of robotic drives use harmonic transmission.
The robots sent to the moon by the United States use harmonic transmissions at their joints. One of the upper arms uses 30 harmonic transmission mechanisms.
For the former Soviet Union, the mobile robot “moon landing” that was sent to the moon, the eight wheels installed in pairs were driven by a closed harmonic transmission mechanism. ROHREN, GEROT R30 robots developed by Volkswagen AG and VERTICAL 80 robots developed by Renault of France have adopted harmonic transmission mechanisms.
