Advantages of Six-Axis Robotic Arms:

Six-axis robotic arms reduce labor requirements, enhance efficiency, lower costs, improve product quality, offer superior safety, and elevate factory image.

The benefits of multi-joint robotic arms include: flexible motion, low inertia, high versatility, the ability to grasp workpieces near the base, and the capacity to navigate around obstacles between the robot body and work machinery. As production demands evolve, higher requirements are placed on articulated arms regarding flexibility, positioning accuracy, and operational space. Articulated arms have transcended traditional concepts, featuring joint counts ranging from three to over a dozen. Their form is no longer limited to human-like arms but adapts to diverse applications. The superior performance of articulated arms is unmatched by single-joint manipulators.

Composition of a Six-Axis Manipulator:

The manipulator primarily consists of three major components: the end-effector, the drive mechanism, and the control system. The end-effector is the component used to grasp workpieces (or tools). Its structure varies based on the shape, size, weight, material, and operational requirements of the object being grasped, including types such as gripping, cradling, and suction. The motion mechanism enables the end-effector to perform various rotations (swivels), translations, or compound motions to execute specified actions, altering the position and orientation of the grasped object. The independent motion modes of the mechanism—such as lifting, telescoping, and rotating—are referred to as the manipulator's degrees of freedom (DOF). Six DOFs are required to grasp objects at any position and orientation in space. DOF is a critical parameter in manipulator design. Greater degrees of freedom enhance the manipulator's flexibility and versatility but also increase structural complexity. Special-purpose manipulators typically have 2 to 3 degrees of freedom. The control system executes specific actions by controlling the motors for each degree of freedom. It simultaneously receives feedback from sensors to establish stable closed-loop control. The core of the control system is usually a microcontroller chip, such as a microcontroller or DSP, programmed to achieve the desired functionality.

Actuator

The actuator of a robotic arm consists of the hand, arm, and torso.

1. Hand

The hand is mounted at the end of the arm. A drive shaft within the arm's inner bore transmits motion to the wrist, enabling rotation, extension, flexion, and finger opening/closing.

The structure of the robotic hand mimics human fingers, categorized into three types: fingerless, fixed-joint, and free-joint. The number of fingers can be two, three, or four, with two-finger configurations being the most common. Various gripper shapes and sizes can be equipped based on the shape and size of the object being grasped to meet operational requirements. A fingerless hand typically refers to a vacuum suction cup or magnetic chuck.

2. Arm

The arm guides the fingers to accurately grasp workpieces and transport them to designated positions. For precise robotic operation, all three degrees of freedom of the arm must be accurately positioned.

3. Torso
The torso serves as the mounting frame for the arm, power source, and various actuators.

Drive Mechanisms

Four primary drive mechanisms are used in robotic arms: hydraulic, pneumatic, electric, and mechanical. Hydraulic and pneumatic drives are most commonly employed.

1. Hydraulic Drive

Hydraulic robotic arms typically comprise a drive system consisting of hydraulic actuators (various cylinders and motors), servo valves, pumps, and reservoirs to power the manipulator's actuators. They offer substantial lifting capacity (often exceeding hundreds of kilograms), featuring compact design, smooth motion, impact resistance, vibration tolerance, and excellent explosion-proof properties. However, hydraulic components demand high manufacturing precision and sealing performance; otherwise, oil leakage may cause environmental contamination.

2. Pneumatic Drive

The drive system typically comprises air cylinders, pneumatic valves, air tanks, and air compressors. Key advantages include readily available air sources, rapid response, simple structure, lower cost, and ease of maintenance. However, precise speed control is challenging, and operating pressure must remain within limits, resulting in lower lifting capacity.

3. Electrically Driven Electric drive is the most widely used drive method for robotic arms. Its advantages include readily available power sources, fast response times, high driving force (jointed types can handle loads up to 400kg), and convenient signal detection, transmission, and processing. It also supports various flexible control schemes. Drive motors typically use stepper motors, with DC servo motors (AC) as the primary drive method. Due to the high motor speeds, reduction mechanisms are usually required (e.g., harmonic drives, RV cycloidal drives, gear drives, worm drives, and multi-link mechanisms). Some robotic arms now employ direct drive (DD) using high-torque, low-speed motors without reduction gears. This simplifies the mechanism while improving control precision.

4. Mechanical Drive

Mechanical drives are used only for applications with fixed motions. Typically, cam-linkage mechanisms are employed to execute specified actions. Their characteristics include reliable and precise operation, high working speeds, and low cost, though they are difficult to adjust. Other approaches include hybrid drives, such as hydraulic-pneumatic or electro-hydraulic hybrid systems.

Control System

Key elements of robotic arm control include work sequence, target position, action timing, movement speed, acceleration/deceleration, etc. Control methods are categorized into point-to-point control and continuous trajectory control.

Control systems can be designed with digital sequential control based on operational requirements. This involves compiling and storing programs, then executing the robotic arm according to predefined sequences. Program storage methods include distributed storage and centralized storage. Distributed storage involves storing different control parameters across multiple devices: sequence data on plugboards, cam drums, or punched tape; positional data on time relays or constant-speed rotary drums. Centralized storage consolidates all control parameters into a single device, such as magnetic tape or magnetic drums. This method is used when sequence, position, timing, and speed must be controlled simultaneously—i.e., in continuous control scenarios.

Punch cards are employed when rapid program changes are required. Switching programs only necessitates replacing a single punch card, and the same card can be reused repeatedly. Punch tape can accommodate programs of unlimited length, but if an error occurs, the entire tape must be replaced. Punch cards have limited information capacity but are easy to replace, store, and reuse. Magnetic cores and magnetic drums are only suitable for applications requiring large storage capacity. The selection of control elements depends on the complexity and precision of the required movements. For complex robotic arms, teach-and-repeat control systems are employed. More intricate robotic systems utilize digital control systems, microcomputer-controlled systems, or microprocessor-controlled systems. Pin-board systems are most commonly used for control systems, followed by cam drums. These drums are equipped with multiple cams, each assigned to a specific motion axis, completing one cycle per revolution of the drum.

Six-axis robotic arms reduce labor requirements, enhance efficiency, lower costs, improve product quality, offer superior safety, and elevate factory image.