Abstract: To overcome the various product defects caused by manual operation of existing paper-making machines, a pneumatic manipulator was designed for high-performance paper-based friction material papermaking processes, employing modularization, integration, and logic analysis methods. This design includes the manipulator's hardware structure, motion flow, and pneumatic control circuit. The manipulator's sensors, terminal position controller, valve island, and controller are integrated using the AS-i bus, providing scalability to meet the design requirements.
0 Introduction
High-performance carbon fiber reinforced paper-based friction materials possess advantages such as a near-perfect static/dynamic friction coefficient ratio of 1, smooth braking, low noise, and environmental friendliness, making them the most ideal wet friction material for automatic transmission systems. Currently, foreign paper-based friction material forming processes are highly mature and automated. In contrast, domestic forming equipment primarily consists of sheet forming machines, which are mainly operated manually, resulting in significant thickness errors and severely impacting product quality stability. To improve the quality and efficiency of mass production, adding robotic arms to existing sheet forming machines is an effective way to replace manual operation.
Robotic arms are a crucial component of transfer mechanisms, using gripping mechanisms to transfer materials from one position and orientation to another along a predetermined trajectory. In recent years, robotic arms have seen increasingly widespread application in automation fields both domestically and internationally, particularly in harsh environments such as those involving toxic substances, radiation, or flammable and explosive materials. Compared to other types of robotic arms, pneumatic robotic arms offer advantages such as simple structure, lower cost, ease of control, convenient maintenance, and long lifespan, making them widely used in various applications. In industrial automation, modular pneumatic robotic arms employing sensors and intelligent components overcome the bulkiness and lack of versatility of traditional pneumatic robotic arms, offering strong practicality and versatility. Furthermore, the use of bus-connected integrated systems, especially valve islands with integrated PLCs and bus interfaces, improves the reliability of pneumatic control systems and simplifies installation and maintenance. Internationally developed pneumatic positioning systems with novel intelligent solenoid valves and feedback control achieve a positioning accuracy of ±0.1mm at a stroke of 300mm and a speed of 2m/s.
This paper addresses the shortcomings of paper-based friction material forming machines, such as low automation and unstable product quality, by designing an automatic pneumatic manipulator for forming paper. It can coordinate with a control system consisting of a valve island and an AS-i bus to form a complete manipulator.
1. Design of the pneumatic manipulator body
1.1 Overall Structural Design of Automatic Wafer Copying Machine
The automatic wafer forming machine is a modification of a manual wafer forming machine by adding a pneumatic manipulator. Its overall structure is shown in Figure 1. Compared to the manual wafer forming machine, it adds a manipulator, an air blowing hood 9, etc. The pneumatic manipulator's movement during the material forming process in the wafer forming machine is described below.
1—Water Pressure Roller
5—Formed Mesh
7—Linear Unit
9—Inflatable Mask
13—Double-acting swing cylinder
14—Material Cylinder
Figure 1 Overall structure of the die copying machine
1—Water Press Roller
2-Y-axis slider driver
3-Z-axis slider driver
4—Finger Cylinder
5—Formed Mesh
6—Main body of the film copying machine
7-DGPL Linear Cylinder
8—Compressed air pipe
9—Inflatable Mask
10—SPCI00 Terminal Position Controller
11—Position Sensor
12—Proportional Directional Control Valve
13—Double-acting swing cylinder
Figure 2. Schematic diagram of robotic arm movements
After the friction material is formed, the material cylinder is supported by the material cylinder support cylinder and lifted by 90 degrees (Figure 1) . Then, the robot arm moves the water pressing roller 1 to roll and dehydrate the forming net 5; the robot arm removes the forming net 5 with the friction material from the support frame, moves it to the right and then up along the guide rail 7 to the top of the worktable and flips it 180 degrees ; the air blowing hood 9 moves down to blow the friction material flat; the forming net 5, robot arm, and material cylinder 14 are reset.
1.2 Design of Robotic Arm Motion Functions
To achieve the series of functions shown in Figure 2, the robotic arm's movements are designed and optimized based on the sequence of manual operations. It utilizes a flexible, modular 3P1R (P: sliding joint, R: rotary joint) robotic arm with three degrees of freedom (1+1/2+1/2+1, excluding fingers). For ease of installation, each component has pre-installed dovetail grooves and other assembly guide rails. The guiding system integrates electrical interfaces and cables/air hoses, enabling the robotic arm to move freely and possessing high rigidity, high strength, and precise guidance and positioning accuracy. The two robotic arms in Figure 2 are symmetrical in structure and have identical functions. Each robotic arm is assembled from five cylinders: DGPL linear unit cylinder 7 (X-axis), small slider drivers 2 and 3 (Y and Z axes), double-acting swing cylinder (180 ° ) 13, and finger cylinder 4.
In the reverse engineering process, two identical robotic arms are used to ensure the rigidity and stability of the mechanism. During operation, the left and right robotic arms work synchronously. To enable synchronized movement of the two robotic arms, cylinders at the same position are controlled by a single valve, the length and direction of the air pipes are perfectly symmetrical, and a position sensor-triggered AND gate (dual-pressure valve) controls the operation. A bidirectional throttle valve ensures identical speeds. Figure 3 illustrates the actions and logic triggers of each cylinder, with the robotic arm's action cycle and functions completed through pre-defined triggers.
Figure 3 Functional diagram of each cylinder
2. Design of the robotic arm control system
2.1 Control System Composition
Because the robotic arm has numerous interfaces and nearly 20 proximity sensors, using a conventional control strategy to connect these pneumatic components, electrical connectors, and sensors would not only be labor-intensive but also prone to incorrect connections or poor contact, leading to a high failure rate. For ease of installation, maintenance, and network control, the robotic arm employs a valve island control system with a PLC and fieldbus, integrated with the AS-i bus, resulting in a complete solution, as shown in Figure 4.
Figure 4. AS-i Bus Independent Local Control Scheme Diagram
The valve island connects the PLC, sensors, and manifold valves with only a single cable, transmitting signals bidirectionally in a specific data format via serial signal transmission. This significantly simplifies the interface, saves wiring time, and makes the control unit compact and practical. Because the valve island has an IP65 protection rating and conforms to DIN standards, it doesn't even require a control box and can be installed near the robot. The AS-i bus, which forms the control signal transmission hub for the robot, not only meets the high-speed transmission requirements for basic data such as simple I/O and on/off signals, but also supports upward expansion in a "pyramid" mode for higher-level byte-level (device-level) and data stream-level applications. A typical network is AS-i—Profibus—IndustrialEthernet. In smaller-scale applications primarily using switching devices, the "pyramid" can be omitted, and a fieldbus monitoring system can be constructed using AS_i and Profibus-DP, offering flexible and convenient configuration options. For robot control, further simplification is possible, retaining only the master controller (PLC/PC/IPC), AS_i master, and slave devices. The host unit acts as the remote I/O port of the controller, and also serves as an independent local controller within the small system, as shown in Figure 4. The CP valve island with an AS-i interface can be equipped with 2 to 8 valve plates. Its integrated PLC supports buses such as AS-i and Profibus. Using an ASI-EVA-MEB-2E1A-Z type AS-i module (IP65) as the host, the valve island is connected to the AS-i network and serves as the starting point of the AS-i network. The slave addresses are set using the address programming device AS-PRG-ADR, thus forming the control network for the robot.
2.2 Solution of key technical problems
2.2.1 Two-point positioning of the cylinder
During the operation of the robotic arm, typical two-point positioning, such as that achieved by a small slider driver and a double-acting swing cylinder, can be accomplished by selecting two endpoint positions and configuring two proximity sensors accordingly. Since there is no strong magnetic field in the robotic arm's workspace, a magnetically coupled sensor is used. When the actuator reaches the corresponding position, it sends a signal, which is transmitted to the controller via the AS-i bus to trigger the next action.
2.2.2 Multi-point positioning of cylinders
For the DGPL rodless cylinder, a key component of the robotic arm, achieving a positioning control scheme with an accuracy of ±1mm at two intermediate points has become one of the main technical challenges. This is because the rodless cylinder needs to achieve continuously adjustable movement speed to reach optimal speed and buffering effect, while significantly reducing cylinder action time and impact. This is very difficult to achieve with traditional pneumatic control components. However, with the maturity of electro-pneumatic proportional/servo control systems and positioning system technologies, pneumatic arbitrary position positioning has become achievable and is being used more and more widely.
1—Guiding device
2—Coupling
3—Displacement sensor (analog type)
4—Actuator (This is a linear cylinder)
5—Grounding wire
6—SPC100 Terminal Position Controller
7—Proportional Directional Control Valve
8—5μm unlubricated filter unit
9—Compressed air source (0.5-0.7MPa)
10—Stop Setpoint
Figure 5. Application of SPCI00 terminal position controller in DGPL linear unit
This paper presents a pneumatic servo control system designed for a high-performance robotic arm. At operating speeds <5 m/s, the positioning accuracy can reach ±0.1-±0.2 mm. The system includes an MPYE servo valve, position sensor, cylinder, and SPC controller, as shown in Figure 5. The controller consists of a parallel neural network and PID control. Utilizing the learning function of the neural network, the gain coefficient is adjusted online to suppress the impact of parameter changes on system stability. Finally, the controller sends a control signal to the servo valve to control the cylinder's motion. The loop is always in closed-loop control, continuously monitoring the controlled variable, and the signal is constantly transmitted to the controller to strive for zero deviation. The controlled variable is continuously compared with the set value, and the controller tries to keep the deviation to zero.
Control operations are accomplished through the interaction between the controller and the controlled system. When setting up the controller, parameters such as the target position, stroke, cylinder bore, working pressure, and load of the robot's DGPL cylinder must be input. Therefore, knowing the approximate parameters of the robot's operation beforehand is crucial. During operation, the SPC digital closed-loop controller executes an arithmetic program that uses the input parameters as characteristic variables. Its main purpose is to generate appropriate variables for the valves. In a single execution, once the system parameters are input and recognized by the controller when defining the servo cylinder task, these parameters are no longer modified by the controller's arithmetic program and are used to calculate temporary parameters. In other words, when parameters such as the robot's load change, the controller parameters need to be readjusted, which was verified during the design simulation.
3. Conclusion
(1) A modular, simple and open pneumatic manipulator control system was constructed by using the AS bus combined with the valve island, and the feasibility of the manipulator body and the control system was initially verified.
(2) The SPCI00 terminal position controller with an electro-pneumatic proportional position control valve can solve the problem of difficult positioning of the robot arm.
(3) The design of the robotic arm combined with the traditional die-cutting machine can improve work efficiency and the quality stability of friction material products.
