PLC controlled stepper motor under precise precision technology

A variety of stepper motor control, precision control requirements of different applications is not the same, how to use the PLC programming software technology to achieve precise control of the stepper motor precision, especially in combination machine allows automatic production line control system, widely used in automated high-precision machining, large construction machinery, precision machinery manufacturing and other industries. The following detailed analysis and interpretation with PLC controlled stepper motor driven slide method CNC, servo control, drive and PLC interface and stepper motor control software logic. 1 Overview In combination machine automatic line in general, depending on the machining accuracy requirements set three slide (1) hydraulic sliding table for cutting capacity, low precision machining roughing operations; (2) mechanical slide for cutting the amount of medium, a semi-finishing operations in certain precision machining; finishing operations (3) CNC sliding table, for a small amount of cutting, high precision required in. The programmable controller (PLC) with its versatility, high reliability, simple instruction set, programming is simple to learn, easy to master, small size, low maintenance, easy installation and a series of field interface, it is widely used in industry Automatic Control. Especially in the combination of machine tools automatic production line of control and CNC machine tools S, T, M function control shows its superior performance. PLC controlled stepper motor open loop servo mechanism is applied to a combination of CNC machine tools automatic production line slider control, eliminating the need for numerical control system of the control system of the unit cost of the unit reduced by 70 to 90%, or even just take up the automatic line control unit PLC of three to five I / O interfaces and <1KB of memory. Especially large automatic line control system can cost significantly. CNC sliding table structure is generally a combination of automatic machine line 2 PLC controlled CNC slide driven by a stepping motor open loop servo mechanism. NC PLC control slide by the partial PLC, ring pulse distributor, stepper motor drives, stepper motors and servo drive mechanism and other components, see Figure 1. Figure 1 servo actuator in the gear Z1, Z2 backlash should take measures to avoid a reverse dead zone or decrease the machining precision; and Vice screw drive should be based on the machining accuracy of the unit to determine whether the choice of ball screw deputy. The use of ball screw, with high transmission efficiency, system rigidity, high transmission precision, long life advantages, but the cost is high and can not be self-locking. PLC control method for controlling factor of 3 NC NC slider slider has three main: 3.1 general hydraulic slide stroke stroke control console and machine slide is to use the position or pressure sensor (limit switch / dead stop iron) to achieve; and CNC sliding table stroke is digitally controlled to achieve. The CNC sliding table arrangement, the trip slider is proportional to the total angle of the stepper motor, stepper motor control as long as the total rotation angle can be. The working principle and characteristics of the stepper motor shows the total angle of the stepper motor is proportional to the number of the control pulse input; therefore can determine the number of pulses output in accordance with displacement of the PLC servo mechanism: n = DL / d (1) the amount of displacement (mm) DL-- servo mechanism where, d - pulse equivalent (mm / pulse) servo 3.2 feed speed control servo feed rate depends on the speed of the stepping motor, and the stepping motor The pulse frequency depends on the input speed; therefore the feed rate can be based on the requirements of the process to determine which PLC output pulse frequency: f = feed rate Vf / 60d (Hz) (2) where Vf-- servos (mm / min) 3.3 feed direction control infeed direction control stepper motor steering control. Stepper motor rotation can change the power-on sequence of the windings of the stepper motor to change its steering; three-phase stepper motor power the order of A-AB-B-BC-C-CA-A ... stepper motor is transferred ; when winding according to A-AC-C-CB-B-BA-A ... stepper motor is powered reverse order. Ring dispenser order to achieve the output signal can be controlled by changing the direction of PLC hardware output, or programmed to change the output pulse sequence to change the order of power stepper motor windings to achieve. 4 PLC software control logic can be seen from the sliding table PLC control method, should the input pulse count and pulse frequency of the stepping motor by the corresponding control. So setting a pulse count and pulse frequency controllable pulse generator in the control software; for low frequency control pulses, you can use the timer PLC configuration, shown in Figure 2. Pulse frequency can be controlled by the timer in constant pulse period, pulse total control, you can set a pulse counter C10. When the pulse number reaches the set value, the counter C10 moves to cut off the pulse generator circuit to stop working. Servo stepper motor stops when no pulse input operation, the servo actuator positioning. When the displacement speed servo actuators are higher, you can use PLC high-speed pulse generator. PLC different frequencies up to its high-speed pulse 4000 ~ 6000Hz. Automatic line for general servo mechanism, its speed can be fully satisfied. Figure 25 servo control, drive and interface 5.1 Stepper motor control system consisting of stepper motor control system consists of a programmable controller, the ring pulse distributor and stepper motor power drives, whose structure shown in Figure 1. PLC control system for generating control pulses; PLC programming output through a certain number of square wave pulse, the stepper motor control angle and then control the feed rate of the servo mechanism; by programming control pulse frequency - both servo feed speed; ring pulse distributor programmable control pulse controller output by power-on sequence assigned to the corresponding stepper motor windings. PLC controlled stepper motor can be used software distributor ring can also be used as shown in Figure 1 hardware distributor ring. PLC soft ring takes more resources, particularly in stepper motor windings Phase M> 4 when the large-scale production lines should be fully considered. Hardware distributor ring, although the hardware configuration is slightly more complicated, but it can save occupy the PLC I / O port points, the market has a variety of special chip can be selected. Stepper motor power drive control pulse PLC output amplified to several tens to hundreds of volts, several security to ten safe driving ability. PLC output interface generally has a certain drive capability, and generally load capacity transistor DC output interface is only a dozen to several dozen volts, several tens to hundreds of milliamps. But for power stepper motor requires tens to hundreds of volts, several security to ten safe driving ability, and therefore should be used to drive the output pulse amplification. 5.2 programmable interfaces such as servo controller hardware distributor ring, then occupied by the PLC I / O port count is less than 5:00, typically only 3:00. Where I occupied a little mouth, as a start control signal; O port occupancy 2:00, a little as the pulse output interface of the PLC, connected to the clock input loop servo system hard, and the other points as the stepper motor steering control signal, connected to the hard phase sequence control terminal distribution ring shown in Figure 3; servo system uses software distributor ring, the interface shown in Figure 4. 6 Application Examples and conclusions will open loop servo PLC control for CNC production line of a large slide, each slide with only four I / O interfaces, saving the CNC control system, which pulse equivalent to 0.01 ~ 0.05mm , feed rate Vf = 3 ~ 15m / min, fully meet the requirements and processing accuracy. Source China Transmission Equipment Network http://www.chuandong360.com