With the development of modern science and technology, PLC has been widely used in industrial control microcomputers.
At present, the joints of industrial robots are mainly controlled by AC servo systems. In this study, the SIEMENS S-200 programmable controller with mature technology, convenient programming, high reliability and small size is applied to the controllable circulating current and reversible system. The robot joint DC servo system is used for servo control of industrial robot joints.
2 Industrial robot joint DC servo system
The industrial robot joint is driven by a DC servo motor, and the forward and reverse rotation of the motor is controlled by the circulating current reversible speed control system to achieve the purpose of servo control of the industrial robot joint.
2.1 Control system structure
The system adopts SIEMEN S7-200 PLC, plus D/A digital-to-analog conversion module, which converts PLC digital signal into analog signal. The regulator ARR, the positive group trigger GTD, the reverse group trigger GTS, and the current feedback device TCV) drive the DC motor to run, and drive the robot joints to act according to the control requirements. The system structure is shown in Figure 1.
Figure 1 Schematic diagram of the structure of the robot joint DC servo system
2.2 The working principle of the system
The principle of the system is shown in Figure 2. The main circuit of the controllable circulating current reversible speed regulation system adopts the cross-connection method. One secondary winding of the rectifier transformer is connected into a Y type, and the other is connected into a △ type. The phases of the two AC power sources are staggered by 30. °, the frequency of the circulating voltage is l2 times the power frequency. In order to suppress the AC circulating current, two equalizing reactors are connected between the two groups of controllable rectifier bridges, and one smoothing reactor is still reserved in the armature circuit.
The control circuit is mainly composed of a speed regulator ASR, a current regulator ACR, a circulating current regulator ARR, a positive group trigger GTD, a reverse group trigger GTS, and a current feedback device TCV (see Figure 2). Among them, the synchronization signals of the two groups of triggers They are respectively taken from the synchronous transformer corresponding to the rectifier transformer.
Figure 2 Schematic diagram of industrial robot joint DC servo system
When the system is given zero, the speed regulator ASR and the current regulator ACR are locked to zero by the zero-speed blocking signal. At this time, the system mainly consists of the circulating current regulator ARR to form a cross-feedback constant current system. Due to the influence of the given circulating current, the two groups of thyristors are in the rectification state, the output voltages are equal in magnitude and opposite in polarity, the DC motor armature voltage is zero, the motor stops, and the output current flows through the two groups of thyristors to form a circulating current . The circulating current should not be too large, generally limited to about 5% of the rated current of the motor. When starting in the forward direction, with the increase of the speed signal Ugn, the blocking signal is released, the speed regulator ASR is output positive, and the motor runs forward. At this time, the positive group current feedback voltage +Ufi2 reflects the sum of the motor armature current and the circulating current; the reverse group current feedback voltage -Uril reflects the armature current, so the main current can be adjusted. However, the circulating current given signal-Ugih and the cross current feedback signal-Ufil added to the input end of the positive group circulating current regulator have little influence on this regulation process. The input voltage of the anti-group circulating current regulator is (+Uk)+(-Ugih)+(Ufi2). With the continuous increase of the armature current, when it reaches a certain level, the circulating current will disappear automatically, and the anti-group thyristor will enter the waiting state. Inverted state. The opposite is true when starting in reverse. In addition, the controllable circulating current reversible speed regulation system still has processes such as inverter braking, reverse braking and feedback braking when braking. Since the start-up process is also a process in which the circulating current is gradually reduced, the circulating current of the system reaches the maximum value when the motor stops. The circulating current helps the system to overcome the switching dead zone and improves the transition characteristics.
3 System programming
The program design plan is to manually input an angle value, let the motor rotate, and detect the rotation angle of the motor through the photoelectric code disc connected to the motor, and turn the rotation angle into a pulse signal. Because the speed of the motor is very fast, only the pulse signal can be sent to the high-speed counter of the PLC. Then compare the pulse record of the counter with the hand input, if the two are equal, the motor has reached the specified angle position, otherwise continue to correct. It is worth noting that since the motor will have a certain inertia from the sudden change of rotation to the stop, a certain error should be allowed in the signal comparison, otherwise the motor will always be in a state of correction. The system program block diagram is shown in Figure 3.
Figure 3 System block diagram
The DC servo system developed based on PLC takes advantage of the strong expansion capability of PLC, and adds a manual delivery device to realize the visual operation of the DC servo system of industrial robot joints. The advantages are: (1) the control of the forward and reverse rotation of the motor can be realized through the program without changing the circuit structure; (2) the motor can be turned in the reverse direction immediately without waiting for the stop to rotate; (3) the motor can be stopped urgently, Avoid motor inertial rotation; (4) easy programming and maintenance.
Responsible editor: gt