With the continuous increase of labor costs, using robots instead of manpower to do some repetitive high-intensity labor is an important direction of modern robot research. The handling robot needs to coordinate the work of the rear wheel drive motor and the front wheel steering gear in the navigation tracing. The motor drive of the handling robot has its special application requirements. It has high requirements on the dynamic performance of the motor. It can reach the specified position required for control at any time and stop the steering gear at any angle. The torque range of the motor drive is large. The high-speed, low-torque working environment of the no-load flat road surface also has the operating conditions of full load climbing, and also requires high operating efficiency. According to the above technical requirements, this paper selects the DC motor with mature control technology and easy to smooth speed regulation as the implementation of the handling robot.
1 system hardware design
1.1 robot motor controller hardware structure
The main controller uses the STM32F107 of the Cortex-M3 core. There are 8 timers inside the controller, among which TIM1_CH1 and TIM8_CH1 are advanced control timer pins, and TIM1_CH1 is used for motor encoder counting. TLM8_CH1 is used for the steering control control reference time. The general-purpose timer pins TIM2CH1, TIM3CH1, TIM4_CH1, and TIM5_CH1 are used to generate the PWM of the upper and lower bridge walls of the motor and servo drive circuit, respectively.
The PA0 port and PB0 port that trigger the EXIT0 interrupt are used for overcurrent interrupt protection of the motor and the servo, respectively. The PA1 port and PB1 port that triggers the EXIT1 interrupt are used for limit protection on both sides of the servo. The motor drive circuit adopts the bootstrap booster chip IR2103 and the MOSFET 75N75. The phase current acquisition of the rear wheel motor and the servo is converted into voltage by the constantan wire, and is sent to the A/D sampling pin of the STM32F107 through amplification and filtering. ADC12_IN1 implements overcurrent protection. Through the host computer serial communication or STM32F107 internal program speed reference, control the motor's forward and reverse, speed and steering steering. Block diagram of the hardware structure of the handling robot motor.
1.2 Module selection and design
1.2.1 Power Driven Design
The motor's power supply is provided by a 24V battery with a rated power of 240W, which is realized by four 75N75 bridge circuits. The 75N75 is a MOSFET power tube with a maximum withstand voltage of 75V, a maximum current rating of 75A, and a motor drive circuit.
Q1, Q4, Q2, and Q3 form two bridges, respectively, which control the forward and reverse rotation of the motor. When the high-side driving MOS transistor is turned on, the source voltage and the drain voltage are the same and are equal to the power supply VCC. Therefore, to achieve normal driving of the MOS transistor, the gate voltage is larger than VCC, which requires a special boosting chip IR2103. . The PWM signal generated by the controller is input to the HIN pin, and EN1 and EN2 of the controller I/O port output are used as enable signals. The output terminal HO can obtain a higher voltage than VCC, and the higher voltage value is exactly the voltage charged across the capacitor. The diode increases the conduction speed, making the on-resistance of the 75N75 smaller and reducing the loss of the switching tube. At the same time, the two output ports HO and LO of the IR2103 have an interlock function to prevent short circuit caused by the straight-through of the upper and lower arms of the motor due to software or hardware errors.
1.2.2 Overcurrent protection design
The installation of overcurrent protection in the motor control system has two meanings: one is to prevent the motor from being overloaded or blocked during normal operation of the motor, so that the current of the armature winding is too large to damage the motor or even cause a fire; When the shoulder movement is started, the current is very large, and it is often impossible to start directly. It is necessary to wait for the excitation winding to gradually establish a magnetic field and then operate normally, and it is desirable that the motor is shoulder-moved as fast as possible. With overcurrent protection, the current is chopped, allowing the motor to start safely and quickly. The schematic of the overcurrent protection is shown in Figure 3.
The phase current of the motor is converted into a voltage signal Vtext by the constantan wire, and the analog quantity AD1 amplified by the operational amplifier is sent to the controller A/D conversion module, and the digital quantity EVA after comparison by the voltage comparator is sent to the controller. External interrupt port.