This article provides a detailed description of the structure, drive, and technical specifications of industrial robots, making it worth a closer look!

1. Common Kinematic Configurations

1. Cartesian Manipulator

Advantages: Easy to implement via computer control and can achieve high precision. Disadvantages: Interferes with work, occupies a large area, has low movement speed, and poor sealing.

① A series of tasks including welding, handling, loading and unloading, packaging, palletizing, de-palletizing, inspection, flaw detection, classification, assembly, labeling, coding, (soft contour) spraying, target tracking, bomb disposal, etc.

② Especially suitable for flexible operations with a variety of products in small batches, playing a crucial role in stability, improving product quality, enhancing labor productivity, and facilitating rapid product updates.

Understanding the Structure, Drive, and Technical Specifications of Industrial Robots

2. Articulated Manipulator (Joint Type)

The joints of articulated robots are all rotating, similar to a human arm, and this is the most common structure in industrial robots. Its working range is quite complex.

① Rapid inspection and product development of automotive parts, molds, sheet metal parts, plastic products, sports equipment, glass products, ceramics, aviation, etc.

② Coordinate measurement and error detection for body assembly, general machinery assembly, etc., for quality control in manufacturing.

③ Rapid prototyping of antiques, artworks, sculptures, cartoon figures, and human portraits.

④ On-site measurement and inspection of complete vehicles.

⑤ Measurement of human shapes, production of medical devices like bones, human shape modeling, and medical aesthetics.

3. SCARA Manipulator

SCARA robots are commonly used for assembly tasks, characterized by their high flexibility in the x-y plane and strong rigidity along the z-axis, thus having selective flexibility. This type of robot has achieved good applications in assembly tasks.

① Widely used for assembling printed circuit boards and electronic components.

② Moving and placing objects, such as integrated circuit boards.

③ Extensively applied in the plastic industry, automotive industry, electronic product industry, pharmaceutical industry, and food industry.

④ Picking parts and assembly work.

4. Spherical Coordinate Manipulator

Characteristics: The working range near the central support is large, the two rotating drive devices are easy to seal, covering a large working space. However, the coordinates are complex, difficult to control, and there are sealing issues with linear drive devices.

5. Cylindrical Coordinate Manipulator

Advantages: Simple calculations; the linear part can use hydraulic drive, providing large power output; capable of reaching inside cavity-type machines. Disadvantages: The space accessible by its arms is limited, unable to reach areas close to columns or the ground.

The linear drive part is difficult to seal and dustproof; during operation, the back end of the arm may collide with other objects within the working range.

6. Redundant Mechanisms

Typically, spatial positioning requires six degrees of freedom, and additional joints can help the mechanism avoid singular configurations. The following image shows a 7-degree-of-freedom manipulator configuration.

7. Closed-loop Structure

A closed-loop structure can improve the rigidity of the mechanism but will reduce the joint’s range of motion, resulting in a certain reduction in working space.

① Motion simulators;

② Parallel machine tools;

③ Micro-operation robots;

④ Force sensors;

⑤ Cell manipulation robots in biomedical engineering, capable of performing cell injection and segmentation;

⑥ Micro-surgical robots;

⑦ Position adjustment devices for large radio astronomical telescopes;

⑧ Hybrid equipment, such as the Tricept hybrid robotic arm module from SMT Company, which is a successful example based on modular design of parallel mechanism units.

Common structural forms of industrial robots (illustration)

2. Main Technical Parameters of Robots

The technical parameters of robots reflect the work they can perform and their highest operational performance, which are crucial considerations in the design and application of robots. The main technical parameters of robots include degrees of freedom, resolution, working space, working speed, and payload.

1. Degrees of Freedom

The number of independent coordinate axes of motion that a robot possesses. The degrees of freedom of a robot refer to the number of independent motion parameters required to determine the position and orientation of the robot’s end effector in space. The opening and closing of fingers, as well as the degrees of freedom of finger joints, are generally not included. The number of degrees of freedom of a robot typically equals the number of joints. Commonly used robots usually do not exceed 5 to 6 degrees of freedom.

2. Joints

Also known as motion pairs, these allow relative motion between the various parts of the robot arm.

3. Working Space

The total spatial area that the installation point of the robot’s arm or end effector can reach. Its shape depends on the number of degrees of freedom and the types and configurations of the various joints. The working space of a robot is usually represented using graphical and analytical methods.

4. Working Speed

The distance moved or angle rotated by the mechanical interface center or tool center point per unit time during uniform motion under working load conditions.

5. Payload

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 size and direction of operating speed and acceleration, with the weight of the parts that can be grasped during high-speed operation generally used as a capacity indicator.

6. Resolution

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

7. Accuracy

Repeatability or repeat positioning accuracy: Refers to the degree of variation when a robot repeatedly reaches a specific target position. Or the dispersion of the robot’s position when it continuously repeats its position under the same position command. It is used to measure the density of error values, i.e., repeatability.

3. Common Materials Used in Robots

1) Carbon structural steel and alloy structural steel: These materials have good strength, especially alloy structural steel, which increases strength by 4 to 5 times, has a large elastic modulus E, and strong resistance to deformation, making them the most widely used materials.

2) Aluminum, aluminum alloys, and other lightweight alloy materials: These materials are characterized by low weight, not very high elastic modulus E, but due to their low density, the ratio of E/ρ can still compare to that of steel. Some rare aluminum alloys have seen significant improvements in quality, such as aluminum alloy with 3.2% (weight percentage) lithium, which increases the elastic modulus by 14%, and the E/ρ ratio by 16%.

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

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

5) Fiber-reinforced composite materials: These materials have an excellent E/ρ ratio and also feature outstanding damping properties. Traditional metal materials cannot achieve such high damping, so the application of composite materials in high-speed robots is increasing.

6) Viscoelastic damping materials: Increasing the damping of the robot’s link components is an effective way to improve the robot’s dynamic characteristics. Currently, many methods are used to increase the damping of structural materials, with one of the most suitable methods for robots being the use of viscoelastic damping materials for constrained layer damping treatment of original components.

4. Main Structures of Robots

(1) Robot Drive Devices

Concept: To make the robot operate, it is necessary to install drive devices for each joint and each degree of freedom. Function: Provide the original power for the actions of various parts and joints of the robot.

Drive systems: These can be hydraulic, pneumatic, electric, or a combination of these systems; they can be direct drive or indirect drive through mechanisms such as synchronous belts, chains, gear systems, harmonic gears, etc.

1. Electric Drive Devices

Electric drive devices have simple energy sources, a wide range of speed variations, high efficiency, and high speed and position accuracy. However, they are often linked with reduction devices, making direct drive difficult.

Electric drive devices can be divided into DC (direct current), AC (alternating current) servo motor drives, and stepper motor drives. DC servo motors have brushes that wear easily and can create sparks. Brushless DC motors are increasingly being used. Stepper motor drives are mostly open-loop control, simple to control but low power, often used in low-precision, low-power robot systems.

Before powering on the electric drive, the following checks should be made:

1) Is the power supply voltage appropriate (over-voltage may damage the drive module)? Ensure that the +/- polarity for DC inputs is not reversed, and check if the motor model or current setting on the drive controller is appropriate (do not set it too high initially);

2) Ensure control signal lines are securely connected; consider shielding issues in industrial environments (e.g., using twisted pairs);

3) Do not connect all necessary wires at the start; only connect the basic system, and once it operates well, gradually connect more.

4) Be clear about the grounding method; it is better to use floating grounding.

5) Closely monitor the motor status within the first half hour of operation, checking for normal movement, sounds, and temperature rise; stop and adjust immediately if any issues arise.

2. Hydraulic Drive

Achieved through high-precision cylinders and pistons, linear motion is realized through the relative movement of the cylinder and piston rod.

Advantages: High power, can connect directly to the driven rods without needing a reduction device, compact structure, good rigidity, and fast response; servo drive has high precision.

Disadvantages: Requires an additional hydraulic source, prone to liquid leaks. It is not suitable for high or low-temperature environments, so hydraulic drive is currently mostly used in very high-power robot systems.

Select suitable hydraulic oil. Prevent solid impurities from entering the hydraulic system and prevent air and water intrusion. Mechanical operations should be gentle and smooth to avoid rough handling, which can cause shock loads, frequent mechanical failures, and significantly shorten service life. Pay attention to cavitation and overflow noise. Always monitor the sounds of the hydraulic pump and overflow valve during operation; if the hydraulic pump produces “cavitation” noise that cannot be eliminated after venting, the cause must be identified and resolved before use. Maintain suitable oil temperatures; the working temperature of the hydraulic system should generally be controlled between 30-80℃.

3. Pneumatic Drive

Pneumatic drive has a simple structure, is clean, and has a quick response but has lower power compared to hydraulic drive, poorer rigidity, higher noise, and speed control is difficult, so it is mainly used in robots with lower precision for point control.

(1) It features fast speed, simple system structure, easy maintenance, and low cost, making it suitable for medium and small load robots. However, due to difficulties in achieving servo control, it is mostly used in programmed control robots, such as in loading and unloading and stamping robots.

(2) In most cases, it is used for two-position or limited point control in medium and small robots.

(3) Most control devices currently use programmable logic controllers (PLC). In flammable and explosive environments, pneumatic logic elements can be used to form control devices.

(2) Linear Transmission Mechanisms.

The transmission device is a key part connecting the power source and the moving links. Depending on the joint form, commonly used transmission mechanisms include linear and rotational transmission mechanisms.

Linear transmission methods can be used for the X, Y, and Z drive of Cartesian robots, radial drive and vertical lift drive of cylindrical coordinate structures, and radial extension drive of spherical coordinate structures.

Linear motion can be converted from rotational motion through transmission elements such as gear racks, lead screws, or can be driven directly by linear motors or by the pistons of cylinders or hydraulic cylinders.

1. Gear Rack Device

Typically, the rack is fixed. The rotational motion of the gear is converted into linear motion of the tray.

Advantages: Simple structure.

Disadvantages: Large backlash.

2. Ball Screw

In the screw and nut’s helical grooves, balls are embedded and guided to continuously circulate through the guiding grooves in the nut.

Advantages: Low friction, high transmission efficiency, no crawling, high precision.

Disadvantages: High manufacturing costs, complex structure.

Self-locking issue: Theoretically, the ball screw pair can be self-locking, but in practice, this self-locking is not used.

The main reasons are: poor reliability or high processing costs; because the ratio of diameter to lead is very large, it is generally accompanied by a set of worm gear or similar self-locking devices.

(3) Rotational Transmission Mechanisms

The purpose of using rotational transmission mechanisms is to convert the high speed output of the motor’s drive source into lower speed while obtaining a larger torque. Commonly used rotational transmission mechanisms in robots include gear chains, synchronous belts, and harmonic gears.

1. Gear Chain

(1) Speed relationship;

(2) Torque relationship.

2. Synchronous Belt

The synchronous belt is a belt with many tooth profiles that meshes with a similarly toothed synchronous pulley. When working, it acts like a flexible gear.

Advantages: No slipping, good flexibility, low cost, high repeat positioning accuracy.

Disadvantages: Certain elastic deformation.

3. Harmonic Gear

The harmonic gear consists of three main parts: rigid gear, harmonic generator, and flexible gear, usually with the rigid gear fixed and the harmonic generator driving the flexible gear to rotate. Main features:

(1) Large transmission ratio, single-stage 50~300.

(2) Smooth transmission, high load capacity.

(3) High transmission efficiency, reaching 70%~90%.

(4) High transmission precision, 3~4 times higher than ordinary gear transmission.

(5) Small backlash, can be less than 3’.

(6) Cannot obtain intermediate output, the rigidity of the flexible gear is relatively low.

Harmonic transmission devices have been widely used in countries with advanced robot technology. For instance, in Japan, 60% of robot drive devices use harmonic transmission.

The robot sent to the moon by the United States used harmonic transmission devices in all its joints, with one arm using 30 harmonic transmission mechanisms.

The Soviet Union’s mobile robot “Lunar Lander” sent to the moon had eight wheels driven by closed harmonic transmission mechanisms. The ROHREN, GEROT R30 robot developed by Volkswagen in Germany and the VERTICAL 80 robot developed by Renault in France also use harmonic transmission mechanisms.

(4) Robot Sensor Systems

1. The sensing system consists of internal sensor modules and external sensor modules to acquire meaningful information from the internal and external environmental states.

2. The use of intelligent sensors enhances the robot’s mobility, adaptability, and level of intelligence.

3. The use of intelligent sensors enhances the robot’s mobility, adaptability, and level of intelligence.

4. For some specific information, sensors can be more effective than human sensory systems.

(5) Robot Position Detection

Rotary optical encoders are the most commonly used position feedback devices. Photoelectric detectors convert light pulses into binary waveforms. The angle of rotation of the shaft is obtained by calculating the number of pulses, and the direction of rotation is determined by the relative phase of two square wave signals.

Inductive synchronizers output two analog signals—the sine signal and cosine signal of the shaft’s rotation angle. The rotation angle is calculated from the relative amplitudes of these two signals. Inductive synchronizers are generally more reliable than encoders but have lower resolution.

Potentiometers are the most direct form of position detection. They are connected in a bridge circuit and can generate a voltage signal proportional to the rotation angle of the shaft. However, they have low resolution, poor linearity, and are sensitive to noise.

Speedometers can output an analog signal proportional to the shaft’s speed. If such speed sensors are not available, speed feedback signals can be obtained by differentiating the detected position with respect to time.

(6) Robot Force Detection

Force sensors are usually installed in three positions on the manipulator’s arm:

1. Installed on the joint driver. It can measure the torque or force output of the driver/reducer itself. However, it cannot effectively detect the contact force between the end effector and the environment.

2. Installed between the end effector and the terminal joint of the manipulator, known as wrist force sensors. Typically, they can measure three to six force/torque components applied to the end effector.

3. Installed at the “fingertips” of the end effector. Typically, these force-sensitive fingers are equipped with strain gauges to measure one to four components of force applied at the fingertips.

(7) Robot-Environment Interaction Systems

1. The robot-environment interaction system is a system that enables industrial robots to connect and coordinate with external devices in the environment.

2. Industrial robots are integrated with external devices into a functional unit, such as processing and manufacturing units, welding units, assembly units, etc. It can also be an integration of multiple robots, multiple machine tools or devices, and multiple parts storage devices.

3. It can also be an integration of multiple robots, multiple machine tools or devices, and multiple parts storage devices into a functional unit to perform complex tasks.

(8) Human-Machine Interaction Systems

The human-machine interaction system is a device that allows operators to participate in robot control and communicate with the robot. This system can be summarized into two main categories: command input devices and information display devices.

5. Robot Control Systems

1. The robot control system

The purpose of “control” is to make the controlled object exhibit the expected behavior of the controller. The basic condition of “control” is to understand the characteristics of the controlled object. The essence is to control the output torque of the driver.

2. Principles of Robot Teaching

The basic working principle of robots is teaching and reproduction, also known as guidance, where the user guides the robot step by step through the actual task operation. During the guidance process, the robot automatically memorizes the position, posture, movement parameters/process parameters of each action taught and automatically generates a program to execute all operations continuously. Once teaching is complete, the robot only needs a start command to accurately perform all operations step by step as taught.

3. Classification of Robot Control:

1) According to feedback, it can be divided into: open-loop control and closed-loop control; open-loop precise control conditions: accurately knowing the model of the controlled object and that this model remains unchanged during the control process.

2) According to the desired control quantity, it can be divided into: position control, force control, and hybrid control; position control is divided into: single-joint position control (position feedback, position speed feedback, position speed acceleration feedback), multi-joint position control, and multi-joint position control can be divided into decomposed motion control and centralized control; force control is divided into direct force control, impedance control, and force-position hybrid control.

3) Intelligent control methods: fuzzy control, adaptive control, optimal control, neural network control, fuzzy neural network control, expert control, and others.

4. Hardware Configuration and Structure of Control Systems:

Due to the large number of coordinate transformations and interpolation calculations involved in the control process of robots, as well as lower-level real-time control, most current robot control systems adopt a layered structure of microcomputer control systems, usually employing a two-level computer servo control system.

1) Specific Process:

After the main control computer receives the job instructions input by the operator, it first analyzes and interprets the instructions to determine the motion parameters of the end effector.

Then, kinematic, dynamic, and interpolation calculations are performed, ultimately deriving the coordinated motion parameters for each joint of the robot. These parameters are output through communication lines to the servo control level as the set signals for each joint’s servo control system. The joint drivers convert this signal from D/A to drive each joint to produce coordinated motion. Sensors feedback the output signals of each joint’s motion back to the servo control level computer to form a local closed-loop control, thus achieving more precise control of the robot’s end effector’s motion in space.

2) PLC-based Motion Control

Two control methods:

1. Using certain output ports of the PLC to issue pulse output instructions to generate pulse drive for the motor, while using general I/O or counting components to achieve closed-loop position control of the motor.

2. Using an externally expanded position control module of the PLC to achieve closed-loop position control of the motor, mainly controlling in high-speed pulse mode, often using point-to-point position control methods.

☞ Source: Robot Network ☞ Editor: You Xiaoxiu☞ Reviewer: Wang Ying

☞ Advertising Cooperation: Sun Ha 13811718902

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Statement: If there are copyright issues with the videos, images, or text used in this article, please inform us immediately, and we will verify the copyright based on the proof materials you provide and pay remuneration according to national standards or delete the content immediately!

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