stepper_motor_drive (961785), страница 3
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A higherresolution brings no measurable advantages. Onthe contrary, the converter clock frequency is already very high in case of low motor revolutions andvery difficult to process by the processor-software.It is recommended to reduce the D/A resolution athigh step frequencies.In case of higher motor revolutions it is more convenient to operate only in full-step, since harmoniccontrol is no longer an advantage as the current hasonly a triangular waveform in the motor winding.PRECISION OF THE MICRO STEPAny desired increase of the position resolution between the full step position has its physical limits.Those who think it is possible to resolve a 7.2° -stepper motor to 1.8° with the same precision as a1.8° - motor in full-step will be received, as there areseveral limits :The rise rate of the torque diagram correspondingto the twisting angle of the rotor for the 7.2° - motoris flatter by a factor of 4 then for the original 1.8° motor.
Consequently with friction or load moment,the position error is larger (fig. 21).For most of the commercial motors there isn’t a sufficiently precise, linear relationship between a sinusoidal-current-diagram and an exact micro stepangle. The reason is a dishomogeneous magneticfield between the rotor and the two stator fields.Above all, problems have to be expected with motors with high pole feeling.
However, there are special stepper motors in which an optimized micro stepoperation has already been considered during theconstruction phase.Figure 19 : The Half-step with Shaping Positioning is Achieved by Simply Changing Reference Voltages.14/17APPLICATION NOTEFigure 20 : L6506 Unit Gives The Possibility to Modulate Separately the Two Reference Voltage Inputs inOrder to obtain a Sinusoidal Phase Current.15/17APPLICATION NOTEFigure 21 : Better Resolution is achieved with Low Degree Motor but More torque is delivered with highDegree Motor.CONCLUSIONSThe above described application examples of modern integrated circuits show that output and efficiency of stepper motors may be remarkablyincreased without any excessive expense increaselike before.16/17Working in limit areas, where improved electronicswith optimized drive sequences allow the use of lessexpensive motors, it is even possible to obtain a costreduction.APPLICATION NOTEInformation furnished is believed to be accurate and reliable.
However, SGS-THOMSON Microelectronics assumes no responsibility forthe consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from itsuse. No license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices orsystems without express written approval of SGS-THOMSON Microelectronics.© 1995 SGS-THOMSON Microelectronics - All Rights ReservedSGS-THOMSON Microelectronics GROUP OF COMPANIESAustralia - Brazil - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco - The Netherlands - Singapore Spain - Sweden - Switzerland - Taiwan - Thaliand - United Kingdom - U.S.A.17/17.
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