Applied Electronics Stepper Motors

 15 October 19:18   

    Stepper Motors are accessories that about-face a shaft by a baby set bend (usually amid 1 and 5 degrees) at a time. This is done actual prcisely, and so they are actual advantageous for appliance acute motion that does not accept any acknowledgment to administer the motor speed. However, they cannot be artlessly apprenticed by a DC or AC voltage like simpler motors; they charge added circuitous chip to drive them.

    For added advice on stepper motors, amuse appointment on the Wikibook of Eletric Motors and Generators. For this book, we will just attending at the basics. There are two kinds of stepper motor - unipolar and bipolar. Bipolar motors are the simplest, so we will attending at those first.

    Bipolar motors accept two coils, anniversary with a affiliation at anniversary end, giving a absolute of four wires. It is posible to analyze which affairs are which, as the attrition amid affairs of altered coils will be infinite. Generally, the access are called in schematics, 1a and 1b getting the two access for one braid and 2a and 2b getting for the additional coil.

    To drive a bipolar stepper motor by one step, the coils accept to be energised in a accurate sequence. Accede just one coil; if 1a is captivated top and 1b is captivated low, the braid is said to conduct forwards. If 1a is at arena and 1b is high, then it conducts backwards. To drive the stepper motor, the coils accept to be switched from administering assiduously to administering backwards alternately.

    The ascribe voltages to the four affairs in adjustment to drive the motor advanced on move are apparent in the table below. The braid polarities generated by this arrangement are apparent on the far appropriate of the table.

    There are some means to aftermath this sequece, from using basal argumentation to accumulation the ascendancy into a micrcontroller. Beneath is the ambit diagram for a motor ambassador create of simple argumentation components. Every time there is a low-to-high trasition on the Move input, the ambit advances the achievement on stage. The DIR ascribe controls the administration of the step; if it is high, it accomplish one way, if it is low it accomplish the additional way.

    However, this ambit cannot drive a stepper motor by itself, as the argumentation outputs cannot accumulation about abundant current. Some array of addition is needed. A bifold adjustment can accommodate the neccessary accepted and voltage reversal:

    Recommended transistors for active stepper motors are MOSFETs IRF510 or IRF530 (N-channel) and IRF9520 or IRF9530 (P-channel). These accept congenital in anchor diodes, so the D1-D8 in the aloft ambit are unnecessary. If you are operating at top currents, it is astute to accumulate them for added protection. About any affectionate of ability transistor (FET or BJT) should be acceptable for this, as continued as the accepted appropriate to drive the motor does not beat the appraisement of the transistor.

    Unipolar motors accept a added circuitous arrangement of braid windings, but a simpler adjustment of driving. Instead of accepting two connections, a unipolar motor braid has three - there is a centre tap on anniversary coil. Unipolar motors accept six leads therfore, in two groups of three. Sometimes there are just five, as the centre curtains may be abutting internally.

    To indentify bare leads, first acquisition the two triplets of affairs - there will be no affiliation at all amid the triplets. Then, acquisition the centre tap - this is the wire with according attrition amid it and the additional two affairs in the triplet. If the centre curtains are abutting calm internally, this will be added difficult, but by aisle and error, it should be possible. Usually, however, the affiliation can be formed out by searching anxiously as the affairs as they appear out of the motor - they will generally be physically aggregate into triplets or affiliated to a baby PCB with the access laid out logically.

    By captivation this centre tap at a accepted voltage (probably ground) and switching the voltage acclimated to ability to motor from one end of the braid to the other, the administration of voltage breeze can be reversed.

    The windings in unipolar motors are bifilar, acceptation there are two coils anguish on top of anniversary additional - one abutting the a adapter to the centre tap and one abutting the b adapter to the centre tap. Because anniversary bisected of the bifilar ambagious is as big as one braid in a bipolar motor, unipolar motors tend to be added than bipolar motors.

    The advantage of unipolar motors is that there is no charge for H-bridge drivers becuase all that needs to be done is to administer a top voltage to one of the connectors if the braid is to be energised - the additional end does not charge an adverse treatment, it can just be broken rather than accepting to be affiliated to the adverse ability rail.

    The arrangement of voltages activated to connectors 1a, 1b, 2a and 2b is the aforementioned as before, so the arrangement of XOR gates and JK flip-flops (or PIC, etc) can be acclimated for unipolar motors. The transistor disciplinarian ambit is simpler, however:

    Any affectionate of ability transistor (FET or BJT) should be acceptable for this, as continued as the accepted appropriate to drive the motor does not beat the appraisement of the transistor. Appropriate transistors are IRF520, TIP31, TIP120, etc. Again, if the transotrs accept congenital in anchor diodes, the separate diodes are not needed, but will not do any accident if larboard in.

    If charge be, unipolar motors can accept the centre curtains abandoned and be acclimated as bipolar motors. This will aftereffect in beneath torque as the coils are alert as continued and so accept alert the attrition and bisected the current. Alternatives, avoid one of the end access and use one bisected of the winding. This should accommodate absolutely the aforementioned characteristics as the motor if acclimated normally.



Tags: drive, motor, power, centre, connection, bipolar, electronics, voltage, circuit, resistance

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