stepping motor calculation

His section covers all types of motors, from the elementary circuitry needed to control a variable reluctance. H-bridge circuitry needed to control a bipolar permanent magnet motor. Each class of drive circuit illustrated with practical examples. However, these examples are not intended to be a comprehensive catalog of commercially available control circuits, nor is it a substitute for the component data sheets by the manufacturers of these items are found.

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This section covers the most elementary control circuitry for each class of vehicles. All of these circuits assume that the motor drive voltage is the voltage of the motor, and this is a significant performance Motor Co., the next in the drive circuit, current limiting coverage of operational efficiency. high drive circuit.

Variable reluctance motor.

General controller for variable reluctance stepping motors are variations on the outline shown in Figure 3.1.

Figure 3.1.

Figure 3.1 boxes are used to represent switches; controller, not shown, is responsible for the control signals for opening and closing the switch at the right time to turn on the engine. In many cases, the control unit is connected to a computer or controller interface directly with software generating the outputs required to control the switches. But in other cases, an additional control circuit is introduced, sometimes not!

Motor windings, solenoids and similar devices are all inductive loads. The current through the motor winding is not on or off, without immediately with endless tensions! When the switch controlling a motor winding is closed, allowing current to flow results of this is to slowly increase the current. If the switch for a motor winding is the result of the voltage spike that can seriously damage the switch unless care in order to treat it properly.

There are two basic ways of dealing with this voltage spike. One is to bridge the motor winding with a diode, and the other is to bridge the motor winding capacitor with Figure 3.2 shows the two methods.

Figure 3.2.

Diodes, as shown in Figure 3.2, to be able to carry the full current through the motor winding. It will be executed in a short period of closed switches, the current through the winding decreases. If such relatively slow diode typically used family 1N400X rapidly in conjunction with the switch, it may be necessary to provide a small capacitor, the book parallel with a diode.

Capacitor in Figure 3.2 is more complex design problems! If the switch is closed, the capacitor to discharge to ground through the switch and the switch must be able to handle these short spike discharge. Resistor in series with the capacitor or in series with the power supply to limit the current when the switch will be stored energy in the motor winding turn on the capacitor to a voltage higher than the voltage, and. need to withstand this voltage. To achieve the size of the capacitor, we equate the two formulas for the energy stored in the resonant circuit.

C P = V2 / 2

P = L I2 / 2

Location:.

P - stored energy in watt seconds or coulomb volts.

C - capacitance in farads.

V - voltage across the capacitor.

L - inductance of motor winding in Henry.

I - current through the motor winding.

The solution for the minimum size of capacitor required to prevent overvoltage switch easily.

C> I2 L / (VB - Vs) 2

Location:.

VB - the breakdown voltage of the switch.

Vs - pressure.

Variable reluctance motors have variable inductance which depends on the angular shaft. So in the worst case would be used to select a capacitor motor inductances are frequently poorly documented, if at all.

Motor winding and capacitor form a resonance circuit in combination. If the drive motor at frequencies near the resonant frequency of this circuit, the current through the motor windings and the motor torque exerted by the engine is quite different from the steady state voltages less! The resonance frequency.

f = 1 / (2 (L C) 0.5).

Again, the electrical resonant frequency of the variable reluctance angle from the shaft. When a variable reluctance motor with the excitation square wave current pulses near the motor winding is operable to cause the magnetic field at the resonant frequency is zero and the greatly reduce the torque available!

Unipolar and hybrid permanent magnet motors.

Joint inspections for unipolar stepping motors are variations on the scheme shown in Figure 3.3.

Figure 3.3.

In Figure 3.3, Figure 3.1 boxes are used to represent switches, control unit, not shown, is responsible for the control signals for opening and closing the switch at the right time to turn on the engine. The control unit is the interface to computer applications or software directly generating the outputs needed to control the switches.

As with drive circuitry for variable reluctance motors, we have created with the inductive kick when each of these switches is turned off deal. Again, we may shunt the inductive kick using diodes, but now, 4 diodes are required, as shown in Figure 3.4.