In the world of modern manufacturing, Computer Numerical Control (CNC) machine tools have become indispensable for precision machining processes. These machines rely on various motors for movement control, and one of the commonly used types is the stepping motor.
Stepping motors offer excellent accuracy and control, making them ideal for CNC applications where precise movements are crucial. In this article, we will delve into the drive control of stepping motors in a CNC machine tool factory, exploring the technology, benefits, and considerations for implementing this critical component of CNC machining.
Benefits of Stepping Motors in CNC Machine Tools
Stepping motors offer several advantages that make them suitable for various CNC machine tool applications:
- Precise Positioning：Stepping motors provide precise positioning with high accuracy and repeatability, making them ideal for applications that require intricate machining and tight tolerances.
- Cost-Effectiveness：Compared to other motor types, stepping motors are generally more cost-effective, making them a popular choice for CNC machine tool manufacturers seeking an economical solution without compromising on performance.
- Simple Control Interface：The control interface for stepping motors is straightforward, consisting of electrical pulses to control the motor’s movement. This simplicity reduces the complexity of the CNC controller, making it easier to program and operate.
- Low Maintenance：Stepping motors have fewer mechanical parts and brushes, leading to lower maintenance requirements and longer service life compared to other motor types.
The Working Method Of Stepper Motor In CNC Machine Factory
Switching from one phase to another is called a beat, and the rotor rotates by a step angle for each beat. Press A_. ¨c_A-… When the power is supplied in the sequence, the rotor of the motor will rotate step by step in this order; on the contrary, if the power is supplied in the order of A-cB÷A-…, the motor will rotate in the reverse direction. The mode of sub-single-phase energization’ is called three-phase Zi three-beat A operation t “single” means that only one phase winding is energized at a time. Three beats. It refers to three times in a cycle, that is, ABC three beats. In the single-three-beat power-on mode, only one phase of the control winding is energized to attract the rotor at a time, which is easy to cause the rotor to oscillate near the equilibrium position, and the running stability is poor; Power-on, it is easy to cause out of step, so it is rarely used in practice – this power-on method is mostly three-phase double-three-beat method.
The three-t double-beat mode means that the power-on mode is AB-BC-CA_AB_… sequence, and two-phase windings are powered on at the same time each time. This energization method has large induction torque, small static error and high positioning accuracy. In addition, there is always a phase control winding energized when the energization state is switched, and the motor works stably and is not easy to lose steps.
Three-phase six-beat power-on mode, that is, the power-on sequence is A-AB-B-BC_c-cA-A-A…, this power-on mode is single-phase and two-phase alternating current, with the characteristics of double two-beat, and the power-on state is doubled, Decrease the step angle by 1.
Control System Of Stepping Motor In CNC Machine Factory
Diagram of the stepper motor drive control system of the CNC machine tool factory. It is composed of a pulse mixing circuit, an addition and subtraction pulse distribution circuit, an acceleration and deceleration circuit, a ring distributor and a power amplifier. The pulse mixing circuit, the addition and subtraction pulse distribution circuit, the acceleration and deceleration circuit and the ring distributor can be realized by hardware circuits. Software can be used to achieve.
1.Pulse Hybrid Circuit
Whether it is the interpolation signal from the CNC system, or various types of error compensation signals, manual feed signals and manual return-to-origin signals, the purpose is to make the table feed forward or backward. First of all, these signals must be mixed into a “forward feed” signal that makes the workbench feed forward or a “reverse feed” signal that makes the workbench feed backward, and the pulse mixing circuit implements this function.
Addition And Subtraction Pulse Distribution Circuit
CNC machine tool factory When the machine tool is feeding in a certain direction under the control of the feed pulse, due to the existence of various compensation pulses, there will also be very individual reverse feed pulses, which are different from the feeding pulses. The appearance of individual pulse commands in the opposite direction means that when the actuator, that is, the stepping motor, is rotating in one direction, it rotates in the opposite direction by a few step angles. The general method is to start from the feeding direction. The same number of reverse compensation pulses are offset in the feed pulse command, which is also the function of the addition and subtraction pulse distribution circuit.
3.Acceleration And Deceleration Circuit Of CNC Machine Factory
The acceleration and deceleration circuit is called the automatic acceleration and deceleration circuit. According to the acceleration and deceleration characteristics of the stepping motor, the frequency change of the level signal entering the stator winding of the stepping motor should be smooth, and there should be a certain time constant. However, since the feed pulse frequency from the addition and subtraction pulse distribution circuit has a jump, in order to ensure that the stepper motor can work normally and reliably, the jump frequency must first be buffered to make it conform to the stepper motor. Acceleration = deceleration special pulse frequency, and then sent to the stator winding of the stepping motor, the acceleration and deceleration circuit is set up for this purpose.
The structure principle of the acceleration and deceleration circuit is shown in Figure 4.7. It consists of a synchronizer, an up and down counter, a digital-to-analog conversion circuit and an RC variable frequency oscillator. The function of the synchronizer is to prevent the feed pulse ^ and the pulse fh from the RC variable frequency oscillator from appearing at the same time, so as to prevent ^ and ^ from entering the reversible counter at the same time, so that the reversible counter does both addition and subtraction at the same time. A count error occurred. The function of the RC variable frequency oscillator is to convert the voltage signal input by the digital-to-analog converter into a pulse signal, and the frequency of the pulse is proportional to the size of the teleporter. The function j of the digital-to-analog conversion circuit is to convert the digital quantity into the analog quantity.
4.Ring Distributor Of CNC Machine Factory
The function of the ring distributor in the CNC machine tool factory is to convert a series of feed pulse commands from the acceleration and deceleration circuit into a level signal that controls the power on and off of the stator winding of the stepping motor. The number and direction of the feed pulses correspond. For example, for a three-phase single-three-beat stepper motor, if “l” means power-on, “.” means power-off, A, B, and c are its three-phase stator windings. After the distributor, A, B, C should be changed in the order of (100) one (010) one (001) one (100)… for each feed pulse command.
There are two types of ring distributors: hardware ring distributor and software ring distributor. The hardware ring distributor is a hardware logic circuit composed of flip-flops and f]circuits. Now there are PM()S and CM()S ring distributor chips with high integration and strong anti-interference on the market for selection, and software ring distributors that can realize pulse sequence distribution by computer software.
5.Power Amplifier
The power amplifier fork is called power driver or power amplifier circuit. The current of the feed control signal from the ring distributor from the CNC machine tool factory is only a few milliamperes, while the stator winding of the stepper motor needs a current of 100 amps. Therefore, a power amplifier is required to amplify the pulse current from the ring distributor enough to drive The stepper motor rotates.
The power amplifiers used in stepping motors are of current type and voltage type. The current type of CNC machine tool factory includes constant current drive type, chopper arrogance type, etc.; voltage split has single voltage type and dual voltage type (high and low voltage type).
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