Robots are the most typical mechatronic digital equipment, possessing high technological added value and a wide range of applications. As a supporting technology for advanced manufacturing and an emerging industry in the information society, they will play an increasingly important role in future production and social development. Since the second half of the 20th century, the global robotics industry has maintained a steady growth momentum. Based on the industrial development and upgrading process of developed countries and the industrialization trend of industrial robots, the Chinese robot market capacity reached approximately tens of thousands of units by 2015.
1. Basic Working Principle of Industrial Robots
An industrial robot is a type of production equipment whose basic function is to provide the motion and power required for operations. Its basic working principle is to automatically realize the manual operation functions and technical requirements by manipulating the movement of various moving parts on the machine. Therefore, in terms of basic functions and working principles, industrial robots and machine tools share similarities: both have end effectors that require position changes, and both achieve these position changes through coordinate motion. However, robots also have their unique requirements. They primarily move in articulated joints, and their flexibility is highly important, while their rigidity and precision requirements are relatively lower.
2 Industrial Robot Structural System
2.1 Industrial Robot Structure
From a functional perspective, a robot can be broken down into four parts: manipulator, end effector, sensor system, and controller. The manipulator consists of a base, arm and wrist, transmission mechanism, and drive system. Its function is to provide the wrist with a certain workspace and adjust the wrist to enable the end effector to perform the required actions for the task. The end effector, also called the hand of an industrial robot, is the component installed on the robot's wrist to directly grasp the workpiece or perform tasks. The sensor system refers to the sensory functions required for the robot to perform work as effectively as a human. Touch is most closely related to robot control. Vision is suitable for detecting the presence of objects and their approximate position and posture. In contrast, touch assists vision, enabling the detection of more subtle states of objects. The controller, the robot's control system, is the brain of the robot and is the main factor determining its functions and performance. It mainly controls the industrial robot's movement position, posture, trajectory, operation sequence, and timing within the workspace. It features simple programming, software menu operation, a user-friendly human-machine interface, online operation prompts, and ease of use. Control systems used in robots include: point-to-point and contour-based; synchronous and asynchronous; digital and analog. The specific control system solution can be selected based on the robot's technical and economic requirements and the characteristics of the technological task.
2.2 Main structural dimensions
The design is based on the main parameters of the AII-V6L industrial robot. The main structural dimensions are shown in Figure 1. The robot's working range is shown in Figure 2.
3.1 Determination of wrist structure
The wrist is the component connecting the arm and the end effector. Its function is to realize the three positional coordinates (degrees of freedom) of the end effector in the workspace, based on the three positional coordinates (degrees of freedom) of the end effector implemented by the arm and base, and then realize the three orientation (orientation) coordinates of the end effector in the workspace, i.e., three rotational degrees of freedom. It connects to and supports the end effector through a mechanical interface. The number of degrees of freedom that the end effector should have is determined according to the robot's operational requirements.
3.2 Determination of basic parameters
After determining the spatial structure and wrist structure, the degrees of freedom for the three postures of wrist rotation, wrist swing, and wrist rotation can be determined. The parameters are shown in Table 1 (parameters are from SSA2000 industrial robot).
Select an AC servo motor with model SGMAH-0IA, rated power of 100W, rated torque of 0.318N·m, rated speed of 3000rpm, and weight of 0.7kg. (2) Selection of B-axis and T-axis motors. Select motors of the same model according to design requirements. Select AC servo motor with model SGMAH-01A.
3.4 Determination of transmission ratio
3.5 Selection of Harmonic Reducers
Harmonic gear reducers are a new type of mechanical transmission speed-changing mechanism. Compared with ordinary gear drives, they are smaller, lighter, and simpler in structure. Compared with ordinary reducers with equivalent transmission ratios, they have 50% fewer parts, reducing both volume and weight by approximately 1/3 or more. They offer a wide transmission ratio range (single-stage transmission ratio 40–350, multi-stage transmission ratios up to 1600–100000), high transmission efficiency (single-stage transmission efficiency ≥85%), high transmission accuracy, and strong load-bearing capacity. Based on the selected motor, an AC servo motor of model SGMAH-OIA with a rated power of 100W, rated torque of 0.318 N·m, and rated speed of 3000 r/min is chosen. Simultaneously, an XBl harmonic reducer, model 25, with a reduction ratio of 40, output torque of 1.0 N·m, and input speed of 3000 r/min is selected. For ease of ordering and maintenance, the same reducer is used for all three shafts.
3.6 Shell Design
The base is made of cast aluminum, with a square structure and an arm thickness of 5-12mm. The body is made of cast aluminum, with a cylindrical structure and an arm thickness of -8mm. The upper arm shell is made of cast aluminum, with a thickness of 6-5mm. The forearm housing and forearm shell are made of cast aluminum, with a square structure; the sides are cast, while the other three sides are cast aluminum sheet. The wrist shell and wrist housing are made of cast aluminum, with a square structure; the two sides, back, and bottom are cast, while the end faces and front are cast aluminum sheet. The arm thickness is 5-8mm. The specific dimensions of other parts are determined by the structure. See Figure 3.
4 Robot Bearing Design
Ball bearings are the most commonly used bearings in robots and manipulator mechanisms. They can withstand radial and axial loads with low friction. Robot-specific bearings feature a four-point contact design and high-precision machining. This type of bearing is 25 times lighter than conventional four-point contact bearings of the same shaft diameter. Its inner ring (or outer ring) is precisely assembled from two half-rings, while the overall outer ring (or inner ring) has a small groove radius of curvature, allowing the steel balls to contact the inner and outer rings at four "points." This increases radial load capacity and allows it to withstand high axial loads in both directions with a compact size, while also providing excellent axial restraint in both directions due to its relatively small axial clearance. Furthermore, its contact angle (typically 35°) is relatively large. Thin-walled four-point contact ball bearings for industrial robots are typically available with and without seals (see Figure 4). They mainly consist of an inner ring, outer ring, cage, steel balls, or a non-contact seal. Both the inner and outer rings are integral structures. The steel balls make four-point contact with the inner and outer rings through the grooves. The cage...
5. Conclusion
Various industrial robots can be used as standalone units or as components of production systems. With changing societal demands and the trend towards multi-variety, small-batch industrial production, the requirements for the flexibility of manufacturing systems are increasing. Industrial robots offer high flexibility, leading to their growing applications within flexible manufacturing systems.
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