Structure and motion process of a simple four-axis linkage manipulator
The structure of the robotic arm is shown in Figure 1 below. It consists of a pneumatic robotic arm (1), an XY axis lead screw assembly (2), a turntable mechanism (3), and a rotating base (4).
Its motion control method is as follows: (1) A pneumatic manipulator with a 360° rotatable angle is driven by a servo motor (with a photoelectric sensor to determine the starting 0 point); (2) A lead screw assembly driven by a stepper motor moves the manipulator along the X and Y axes (with x and y axis limit switches); (3) A turntable mechanism that can rotate 360° can drive the manipulator and lead screw assembly to rotate freely (its electrical drive part is composed of a DC motor, photoelectric encoder, proximity switch, etc.); (4) The rotating base mainly supports the above 3 parts; (5) The opening and closing of the pneumatic manipulator is controlled by air pressure (the manipulator grips tightly when inflated and releases air when deflated).
Its working process is as follows: when the goods arrive, the robotic arm system starts to move; the stepper motor controls the downward movement, while another stepper motor controls the horizontal axis to move forward; the servo motor drives the robotic arm to rotate to the position where it can grab the goods, and then it is inflated, and the robotic arm clamps the goods.
A stepper motor drives the vertical axis to rise, while another stepper motor drives the horizontal axis to move forward. The turntable DC motor rotates, causing the robot arm to move as a whole, rotating to the cargo receiving position. The stepper motor then drives the vertical axis to descend again. After reaching the designated position, the air valve releases air, and the robot arm releases the cargo. The system returns to its original position, ready for the next action.
II. Controller Selection <br />To achieve precise control, based on market conditions, the following key components are selected:
1. The stepper motors and their drivers for the robot's longitudinal (Y-axis) and transverse (X-axis) axes are selected from Beijing Sitong Motor Technology Co., Ltd. The selected stepper motors are the 42BYG250C two-phase hybrid stepper motors, with a step angle of 0.9°/1.8° and a current of 1.5A. M1 is the transverse axis motor, driving the robot's extension and retraction; M2 is the longitudinal axis motor, driving the robot's rise and fall. The selected stepper motor driver is the SH-20403 model. This driver uses 10-40V DC power supply, H-bridge bipolar constant phase current drive, eight selectable output currents up to 3A, seven selectable microstepping modes up to 64 microsteps, opto-isolated input signals, a standard single-pulse interface, offline hold function, and a semi-enclosed housing to adapt to harsher working environments. It also provides an energy-saving automatic half-current mode. The internal switching power supply design of the driver ensures that it can adapt to a wide voltage range, and users can select between 10-40VDC according to their specific needs. Generally, a higher rated power supply voltage is beneficial for increasing the high-speed torque of the motor, but it will increase the loss and temperature rise of the driver. This driver has a maximum output current of 3A/phase (peak). Eight states, corresponding to eight output currents, ranging from 0.9A to 3A, can be combined using the 5th, 6th, and 7th positions of the six-position DIP switch on the driver panel to suit different motors. This driver offers seven operating modes: full step, improved half step, 4 microstep, 8 microstep, 16 microstep, 32 microstep, and 64 microstep. These modes can be configured using the 1st, 2nd, and 3rd positions of the six-position DIP switch on the driver panel.
Robotic arm structure diagram
2. The servo motor and its driver: The robot's rotational motion uses a Panasonic A-series low-inertia MSMA5AZA1G servo motor, with a rated output of 50W and 100/200V shared. The rotary encoder is incremental (2500 pulses/r, 10000 pulses/r resolution, 11 leads). It has an oil seal but no brake, and the shaft uses a keyway connection. This motor uses Panasonic's unique algorithm, which doubles the speed frequency response to 500Hz; the positioning over-adjustment time is reduced to 1/4 of that of previous Panasonic V-series servo motors. It features resonance suppression, control, and full closed-loop control functions, which can compensate for insufficient mechanical rigidity, thereby achieving high-speed positioning. It can also form a full closed-loop control by connecting an external high-precision grating ruler, further improving system accuracy. It has two automatic gain adjustment modes: conventional automatic gain adjustment and real-time automatic gain adjustment. It is also equipped with RS-485 and RS-232C communication ports, allowing the host controller to control up to 16 axes simultaneously. The servo motor driver is the A-series MSDA5A3A1A, which is suitable for small inertia motors.
3. The 360° rotatable turntable mechanism is driven by a brushless DC motor. The system uses a 57BL1010H1 brushless DC motor manufactured by Beijing Heshili Company, which features a wide speed range, high low-speed torque, smooth operation, low noise, and high efficiency. The brushless DC motor driver uses the BL-0408 driver manufactured by Beijing Heshili Company, which adopts a 24-48V DC power supply and has start/stop and direction control, overcurrent, overvoltage, and stall protection. It also features fault alarm output, external analog speed regulation, and rapid braking stop.
4. An OMRON E6A2 incremental rotary encoder is mounted on a 360° rotatable turntable mechanism.
5. PLC Selection: Based on the system design requirements, the OMRON CPM2A miniature PLC was selected. The CPM2A integrates various functions within a compact unit, including synchronous pulse control, interrupt input, pulse output, analog signal setting, and clock functions. The CPM2A's CPU unit is also an independent unit, capable of handling a wide range of mechanical control applications, making it an ideal product for use as an integrated control unit within equipment. Complete communication capabilities ensure communication with personal computers, other OMRON PCs, and OMRON programmable terminals. These communication capabilities allow the four-axis linkage simple robot to be easily integrated into industrial control systems.
3. Software Programming 1. Software Flowchart The flowchart is the foundation of PLC programming. Only by designing a flowchart can the ladder diagram and statement list be written smoothly and conveniently, ultimately completing the program design. Therefore, writing the flowchart is crucial and is the first task in program design. Based on the control requirements of a four-axis linkage simple robot, the flowchart is shown in Figure 2.
Software Flowchart
2. Program Section Due to space limitations, only the first two program segments are listed here for readers' reference, as shown in Figure 3.
Program List
IV. Conclusion <br />The various movements and states of the four-axis linkage simple robot are controlled by a PLC. This not only meets the requirements of numerous buttons, switches, and position detection points needed for manual, semi-automatic, and automatic operation modes, but also enables network communication and control by connecting it to a computer via interface components, thus allowing the four-axis linkage simple robot to be easily embedded into industrial production lines.
