Detailed explanation | detailed explanation of internal mechanism of industrial robot

Reading guide

Xiaobian will tell you about the internal structure of industrial robots today , Teach everyone to control 、 drive 、 Transmission 、 Execution and other basic knowledge about robots .

Don't underestimate this basic content , As the saying goes, sharpening a knife is not a mistake for cutting firewood , With a solid foundation , It is very helpful for future study and development .

Before understanding the construction of general industrial robots

Let's first look at the animation simulation of robot arm joints

Germany kuka Industrial robots

Main internal structure

One 、 Robot drive   

Concept ： To make the robot run , It is necessary to place the transmission device for each joint, that is, each degree of freedom of motion .

effect ： Provide all parts of the robot 、 The motive force of each joint action .

Drive system ： It can be hydraulic transmission 、 Pneumatic transmission 、 Electric drive , Or an integrated system that combines them ; It can be driven directly or through the synchronous belt 、 chain 、 gear train 、 Harmonic gear and other mechanical transmission mechanisms for indirect drive .

1、 Electric drive

The energy of the electric drive is simple , The speed variation range is large , Efficient , High speed and position accuracy . But they are mostly connected with the speed reducer , Direct drive is difficult .

The electric drive device can be divided into DC (DC)、 communication (AC) Servo motor drive and stepping motor drive . The brush of DC servo motor is easy to wear , And easy to form sparks . Brushless DC motor has also been more and more widely used . Stepper motor drive is mostly open-loop control , Simple control but low power , It is mostly used in low precision and low power robot systems .

The following checks shall be made before the electric motor is powered on for operation ：

1） Whether the power supply voltage is appropriate （ Overvoltage is likely to cause damage to the drive module ）;  For DC input +/- The polarity must not be connected wrong , Whether the motor model or current setting value on the drive controller is appropriate （ Don't be too big at first ）;

2） The control signal line is firmly connected , It is best to consider shielding in industrial sites （ If twisted pair is used ）;

3） Don't connect all the wires you need to connect at the beginning , Only connect into the most basic system , After running well , Then gradually connect ;

4） Be sure to find out the grounding method , Still use floating without receiving ;

5） The state of the motor shall be closely observed within half an hour of starting operation , If the movement is normal , Sound and temperature rise , If any problem is found, stop the machine immediately and adjust it .

2、 Hydraulic drive

Through high-precision cylinder and piston to complete , The linear motion is realized through the relative motion of the cylinder block and the piston rod .

advantage ： High power , The speed reducer can be omitted and directly connected with the driven rod , Compact structure , Good stiffness , Fast response , Servo drive has high precision .

shortcoming ： Additional hydraulic source is required , Prone to liquid leakage , Not suitable for high 、 Low temperature occasions , Therefore, hydraulic drive is mostly used in super high-power robot systems .

Choose the right hydraulic oil . Prevent solid impurities from mixing into the hydraulic system , Prevent air and water from invading the hydraulic system . Mechanical operation shall be gentle and smooth, and rough operation shall be avoided , Otherwise, shock load will inevitably occur , Make mechanical faults occur frequently , Greatly shorten the service life . Pay attention to cavitation and overflow noise . Pay attention to the sound of hydraulic pump and overflow valve during operation , If the hydraulic pump appears “ cavitation ” noise , It cannot be eliminated after exhaust , Find out the cause and eliminate the fault before using . Maintain proper oil temperature . The working temperature of the hydraulic system is generally controlled at 30～80℃ In between .

3、 Air pressure drives

The structure of pneumatic drive is simple , clean , Quick action , It has a buffering effect . But compared with hydraulic drive , Less power , Poor stiffness , It's noisy , Speed is not easy to control , Therefore, it is mostly used for point control robots with low precision .

（1） Fast speed 、 The system structure is simple , Easy to maintain 、 Low price characteristics . Suitable for 、 In small load robots . But because it is difficult to realize servo control , It is mostly used in robot controlled by program , As on 、 It is widely used in blanking and stamping robots .

（2） In most cases, it is used to realize two position or finite point position control 、 In small robots .

（3） At present, most control devices choose programmable controller (PLC controller ). It's flammable 、 In explosive situations, pneumatic logic elements can be used to form a control device .

Two 、 Linear transmission mechanism   

The transmission device is the key part connecting the power source and the moving connecting rod , According to the joint form , The commonly used transmission mechanisms include linear transmission and rotary transmission .

The linear transmission mode can be used in the design of rectangular coordinate robot X、Y、Z To drive , Radial drive and vertical lifting drive of cylindrical coordinate structure , And the radial telescopic drive of spherical coordinate structure .

Linear motion can be achieved through rack and pinion 、 Transmission elements such as lead screw and nut convert rotary motion into linear motion , It can also be driven by linear drive motor , It can also be directly generated by the piston of the cylinder or hydraulic cylinder .

1、 Rack and pinion unit

Usually the rack is fixed . The rotational motion of the gear is converted into the linear motion of the supporting plate .

advantage ： Simple structure .

shortcoming ： The return difference is large .

2、 Ball screw

Insert the ball into the spiral groove of the lead screw and nut , The ball can circulate continuously through the guide groove in the nut .

advantage ： Little friction , High transmission efficiency , No crawling , High precision .

shortcoming ： High manufacturing cost , Complicated structure .

Self locking problem ： In theory, the ball screw pair can also be self-locking , However, this self-locking is not used in practical application .

The main reason is the poor reliability , Or the processing cost is very high ; Because the diameter is much larger than the lead , Generally, a set of self-locking device such as worm gear and worm is added .

3、 ... and 、 Rotary transmission mechanism  

The purpose of adopting the rotary transmission mechanism is to convert the higher speed output by the driving source of the motor into a lower speed , And obtain a larger torque . The most widely used rotary transmission mechanism in robot is gear chain 、 Synchronous belt and harmonic gear .

1、 Gear chain

（1） Speed relationship

（2） Moment relation

2、 Synchronous belt

A synchronous belt is a belt with many teeth , It meshes with the synchronous belt pulley with the same profile teeth . It works like a soft gear .

advantage ： No sliding , Good flexibility , Cheapness , High accuracy of repeated positioning .

shortcoming ： It has certain elastic deformation .

3、 Harmonic gear

Harmonic gears consist of rigid gears 、 Harmonic generator and flexible gear are three main parts , Generally, rigid gears are fixed , The harmonic generator drives the flexible gear to rotate . 

The main features ：

(1) High transmission ratio , Single stage is 50—300;

(2) Smooth transmission , High bearing capacity ;

(3) High transmission efficiency , Can be up to 70%—90%;

(4) High transmission accuracy , Higher than ordinary gear transmission 3—4 times ;

(5) The difference is small , Less than 3’;

(6) Cannot get intermediate output , The flexspline has low stiffness .

Harmonic drive has been widely used in countries with advanced robot technology . In Japan alone , Design of robot driving device 60％ All adopt harmonic drive .

Robots sent to the moon by the United States , Each joint part of the utility model adopts a harmonic drive device , One of the upper arms is used 30 A harmonic drive mechanism .

The mobile robot sent to the moon by the former Soviet Union “ Lunar lander ”, They are installed in pairs 8 All wheels are driven separately by closed harmonic drive mechanism . Developed by Volkswagen AG ROHREN、GEROT R30 And the robot developed by Renault of France VERTICAL 80 All robots adopt harmonic transmission mechanism .

Four 、 Robot sensing system   

1、 The sensing system is composed of internal sensor module and external sensor module , To obtain meaningful information in the internal and external environmental state .

2、 The use of intelligent sensors improves the mobility of the robot 、 The level of adaptability and intelligence .

3、 For some special information , Sensors are more effective than human sensory systems .

5、 ... and 、 Robot position detection

Rotary optical encoder is the most commonly used position feedback device . Photodetectors convert light pulses into binary waveforms . The rotation angle of the shaft is obtained by calculating the number of pulses , The direction of rotation is determined by the relative phases of the two square wave signals .

The inductosyn outputs two analog signals —— Sine signal and cosine signal of shaft rotation angle . The rotation angle of the shaft is calculated from the relative amplitude of the two signals . Inductosyn is generally more reliable than encoder , But its resolution is low .

Potentiometer is the most direct form of position detection . It's connected in a bridge , It can generate a voltage signal proportional to the shaft angle . however , Due to low resolution 、 Poor linearity and sensitivity to noise .

The tachometer can output an analog signal proportional to the speed of the shaft . If there is no such speed sensor , The speed feedback signal can be obtained by the difference between the detected position and time .

6、 ... and 、 Machine manpower detection

The force sensor is usually installed in the following three positions of the operating arm ：

1、 Mounted on the joint drive . Measurable drive / The output of the torque or force of the reducer itself . However, the contact force between the end effector and the environment cannot be well detected .

2、 It is installed between the end effector and the end joint of the operating arm , It can be called wrist force sensor . Usually , Three to six forces applied to the end effector can be measured / Moment component .

3、 Installed on the end effector “ Fingertips ” On . Usually , These forceful fingers have built-in strain gauges , You can measure one to four components acting on your fingertips .

7、 ... and 、 robot － Environmental interaction system

1、 robot - Environmental interaction system is a system that realizes the interaction and coordination between industrial robots and equipment in the external environment .

2、 Industrial robots are integrated with external equipment into a functional unit , Such as processing and manufacturing unit 、 Welding unit 、 Assembly unit, etc ; It can also be multiple robots 、 Multiple machine tools or equipment 、 Integration of multiple parts storage devices, etc .

3、 It can also be multiple robots 、 Multiple machine tools or equipment 、 Multiple parts storage devices are integrated into a functional unit to perform complex tasks .

8、 ... and 、 Human computer interaction system  

Human computer interaction system is a device that enables operators to participate in robot control and contact with robots . The system can be divided into two categories : Instruction setting device and information display device

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