單片機控制步進電機的系統畢業論文-資料下載頁

　　

【正文】 motor may be rated at 6V and 1A per phase. Therefore, with two phases energizedthe motor has a rated power dissipation of 12 watts. It is normal practice to rate a stepper motor at the power dissipation level where the motor case rises 65176。C above the ambient in still air. Therefore, if the motor can be mounted to a heatsink it is often possible to increase the allowable power dissipation level. This is important as the motor is designed to be and should be used at its maximum power dissipation ,to be efficient froma size/output power/cost point of view. When to Use a StepperMotor A stepper motor can be a good choice henever controlled movement is equired. They can be used to advantage in applications where you need to control rotation angle, speed, position and synchronism. Because of the inherent advantages listed previously, stepper motors have found their place in many different applications. Some of these include printers, plotters, highend office equipment, hard disk drives, medical equipment, fax machines, automotive and many more.The Rotating Magnetic Field When a phase winding of a stepper motor is energized with current a magnetic flux is developed in the stator. The d When a phase winding of a stepper motor is energized with current a magnetic flux is developed irection of this flux is determined by the “Right HandRule” which states: “If the coil is grasped in the right hand with the fingers pointing in the direction of the current in the winding (the thumb is extended at a 90176。 angleto the fingers), then the thumb will point in the direction of the magnetic field.”Figure 2 shows the magnetic flux path developed when phase B is energized with winding current in the direction shown. The rotor then aligns itself so that the flux opposition is minimized. In this case the motor would rotate clockwise so that its south pole aligns with the north pole of the stator B at position 2 and its north pole aligns with the south pole of stator B at position 6. To get the motor to rotate we can now see that we must provide a sequence of energizing the stator windings in such a fashion that provides a rotating magnetic flux field which the rotor follows due to magnetic attraction.Figure 2 Magnetic flux path through a twopole stepper motor with a lag between the rotor and stator.Torque GenerationThe torque produced by a stepper motor depends on several factors.? The step rate? The drive current in the windings? The drive design or typeIn a stepper motor a torque is developed when the magnetic fluxes of the rotor and stator are displaced from each other. The stator is made up of a high permeability magnetic material. The presence of this high permeability material causes the magnetic flux to be confined for the most part to the paths defined by the stator structure in the same fashion that currents are confined to the conductors of an electronic circuit. This serves to concentrate the flux at the stator poles. The torque output produced by the motor is proportional to the intensity of the magnetic flux generated when the winding is energized.The basic relationship which defines the intensity of the magneticflux is defined by:H = (N i) 247。 l N = The number of winding turnsi = currentH = Magnetic field intensityl = Magnetic flux path lengthThis relationship shows that the magnetic flux intensity and consequently the torque is proportional to the number of winding turns and the current and inversely proportional to the length of the magnetic flux path. From this basic relationship one can see that the same frame size stepper motor could have very different torque output capabilities simply by changing the winding parameters. More detailed information on how the winding parameters affect the output capability of the motor can be found in the application note entitled “DriveCircuit Basics”.Stepping ModesThe following are the most mon drive modes.? Wave Drive (1 phase on)? Full Step Drive (2 phases on)? Half Step Drive (1 amp。 2 phases on)? Micro stepping (Continuously varying motor currents)For the following discussions please refer to the figure 3. Figure 3 Unipolar and bipolar wound stepper motors. In Wave Drive only one winding is energized at any given time. The stator is energized according to the sequence A174。B 174。A 174。 B and the rotor steps from position 8 174。2 174。 4 174。6. For unipolar and bipolar wound motors with the same winding parameters this excitation mode would result in the same mechanical position. The disadvantage of this drive mode is that in the unipolar wound motor you are only using 25% and in the bipolar motor only 50% of the total motor winding at any given time. This means that you are not getting the maximum torque output from the motor. In Full Step Drive you are energizingtwo phases at any given stator is energized according to the sequence AB 174。AB 174。AB 174。AB and the rotor steps from position 1174。3174。5 174。7 . Full step mode results in the same angular movement as 1 phase on drive but the mechanical position is offset by one half of a full step. The torque output of the unipolar wound motor is lower than the bipolar motor (for motors with the same winding parameters) since the unipolar motor uses only 50% of the available winding while the bipolar motor uses the entire winding. Half Step Drive bines both wave and full step (1amp。2 phases on) drive modes. Every second step onlyone phase is energized and during the other steps one phase on each stator. The stator is energized according to the sequence AB 174。B 174。 AB 174。 A 174。AB 174。B 174。AB174。A and the rotor steps from position 1 174。 2 174。 3 174。4 174。5 174。6 174。 7 174。 8. This results in angular movements that are half of those in 1 or 2phaseson drive modes. Half stepping can reduce a phenomena referred to as resonance which can be experienced in 1 or 2phaseson drive modes.The excitation sequences for the above drive mo