Saturday, July 18, 2009
H-Bridge
This circuit drives small DC motors up to about 100 watts or 5 amps or 40 volts, whichever comes first. Using bigger parts could make it more powerful. Using a real H-bridge IC makes sense for this size of motor, but hobbyists love to do it themselves, and I thought it was about time to show a tested H-bridge motor driver that didn't use exotic parts.
http://www.bobblick.com/techref/projects/hbridge/hbridge.html
H-bridge using P and N channel FETs
This H-bridge uses MOSFETs for one main reason - to improve the efficiency of the bridge. When BJT transistors (normal transistors) were used, they had a saturation voltage of approximately 1V across the collector emitter junction when turned on. My power supply was 10V and I was consuming 2V across the two transistor required to control the direction of the motor. 20% of my power was eaten up by the transistors. I tried darlingtons etc... nothing worked. The transistors also would get quite hot - no room for heatsinks.
http://www.armory.com/~rstevew/Public/Motors/H-Bridges/Blanchard/h-bridge.htm
N-Channel H-bridge Motor Drive
In low voltage motor drives, it is common practice to use
complementary MOSFET half-bridges to simplify the gate
drive design. However, the P-channel FET within the
half-bridge usually has a higher on resistance or is larger
and more expensive than the N-channel FET. The alternative
solution is to design in an N-channel half-bridge.
http://www.eetkorea.com/ARTICLES/2004MAY/2004MAY18_BD_MSD_PD_AN.PDF
Comparator Controlled H-Bridge Circuits (LM311)
The next two circuits are simple Bi-Polar H-Bridge circuits. The bridges are controlled by a pair of LM311 voltage Comparators.
The LM311 Voltage Comparator has several unique features, one of which is an output transistor with an open emitter as well as the typical open collector. This allows the output transistor of the comparator to sit between the bases of the power transistors.
http://home.cogeco.ca/~rpaisley4/HBridge.html
Robot Motor control
In order to control the speed/torque of a motor, a so called H-bridge can be used. I built/designed one myself, using 4 MOSFETs.
http://www.iwhat.nl/rienatmarobi/bots/Wheeley/motor/index.html
Bidirectional operation (H-bridge circuit)
We have achieved speed control and have made a powerful drive circuit. However in robotic work we also usually want to be able to drive a motor either clockwise or counterclockwise. Before we discuss the use of transistors to solve this problem
http://www.mech.uwa.edu.au/NWS/How_to_do_stuff/micro_crash_course/pwm/
H-Bridge
This circuit drives small DC motors up to about 100 watts or 5 amps or 40 volts, whichever comes first. Using bigger parts could make it more powerful. Using a real H-bridge IC makes sense for this size of motor, but hobbyists love to do it themselves, and I thought it was about time to show a tested H-bridge motor driver that didn't use exotic parts.
http://www.bobblick.com/techref/projects/hbridge/hbridge.html
H-bridge using P and N channel FETs
This H-bridge uses MOSFETs for one main reason - to improve the efficiency of the bridge. When BJT transistors (normal transistors) were used, they had a saturation voltage of approximately 1V across the collector emitter junction when turned on. My power supply was 10V and I was consuming 2V across the two transistor required to control the direction of the motor. 20% of my power was eaten up by the transistors. I tried darlingtons etc... nothing worked. The transistors also would get quite hot - no room for heatsinks.
http://www.armory.com/~rstevew/Public/Motors/H-Bridges/Blanchard/h-bridge.htm
N-Channel H-bridge Motor Drive
In low voltage motor drives, it is common practice to use
complementary MOSFET half-bridges to simplify the gate
drive design. However, the P-channel FET within the
half-bridge usually has a higher on resistance or is larger
and more expensive than the N-channel FET. The alternative
solution is to design in an N-channel half-bridge.
http://www.eetkorea.com/ARTICLES/2004MAY/2004MAY18_BD_MSD_PD_AN.PDF
Comparator Controlled H-Bridge Circuits (LM311)
The next two circuits are simple Bi-Polar H-Bridge circuits. The bridges are controlled by a pair of LM311 voltage Comparators.
The LM311 Voltage Comparator has several unique features, one of which is an output transistor with an open emitter as well as the typical open collector. This allows the output transistor of the comparator to sit between the bases of the power transistors.
http://home.cogeco.ca/~rpaisley4/HBridge.html
Robot Motor control
In order to control the speed/torque of a motor, a so called H-bridge can be used. I built/designed one myself, using 4 MOSFETs.
http://www.iwhat.nl/rienatmarobi/bots/Wheeley/motor/index.html
Bidirectional operation (H-bridge circuit)
We have achieved speed control and have made a powerful drive circuit. However in robotic work we also usually want to be able to drive a motor either clockwise or counterclockwise. Before we discuss the use of transistors to solve this problem
http://www.mech.uwa.edu.au/NWS/How_to_do_stuff/micro_crash_course/pwm/
Saturday, July 11, 2009
Speed Controller Circuit
The robot I intend to build will be a 4WD bot with a skid steer system so to do this best I have opted to build 2 a controller system moulded around a 4QD DCI111. (A DCI111 converts radio signals into useable signals) Because of this the inputs on my controllers have to be similar to the 4QD units. The next things to consider are the motors that I will be using. Bosch 750’s seem to be quite popular (so are ford escorts and they are crap) so I will just go ahed and use the many starter motors that I have lying around. This results in 
more
DC Motor Control & Interfacing Circuit
A permanent magnet DC motor responds to both voltage and current. The steady state voltage across a motor determines the motor’s running speed, and the current through its armature windings determines the torque. Apply a voltage and the motor will start running in one direction; reverse the polarity and the direction will be reversed. If you apply a load to the motor shaft, it will draw more current, if the power supply does not able to provide enough current, the voltage will drop and the speed of the motor will be reduced. However, if the power supply can maintain voltage while supplying the current, the motor will run at the same speed. In general, you can control the speed by applying the appropriate voltage, while torque is controlled by current. In most cases, DC motors are powered up by using fixed DC power supply, therefore; it is more efficient to use a chopping circuit.
more
PWM D.C. motor drive Circuit
This circuit is a very compact switching regulator for small DC motors. I use it for my small printed circuit board drill (18 Volt, 1.5 Amp), but it is suitable for many other applications (e.g. 12V DC halogen dimmer).
more
Back EMF PM Motor Speed Control Circuit
A 12 V control supply and a TRW BL11, 30 V motor are used; with minor changes other motor and control voltages can be accommodated. For example, a single 24 V rail could supply both control and motor voltages. Motor and control voltages are kept separate here because CMOS logic is used to start, stop, reverse and oscillate the motor with a variable delay between motor reversals.
more
Bidirectional DC Motor Speed Controller
This kit allows controlling the speed of a DC motor in
both the forward and reverse direction. The range of
control is from fully OFF to fully ON in both directions.
This kit overcomes both these problems. The direction and
speed is controlled using a single potentiometer. Turning
the pot in one direction causes the motor to start spinning.
Turning the pot in the other direction causes the motor to
spin in the opposite direction. The center position on the
pot is OFF, forcing the motor to slow and stop before
changing direction.
more pdf
PWM DC Motor Speed Control
The left half of the 556 dual timer IC is used as a fixed frequency square wave oscillator. The oscillator signal is fed into the right half of the 556 which is configured as a variable pulse width one-shot monostable multivibrator (pulse stretcher).
more
DC Motor Controlled with PWM Resources
Here is a description of the driver circuit. It's based on the Microchip AN531 Application Note titled "Remote Positionner". The circuit given in the application Note do not work , so this is a correction of the circuit:
more
DC MOTOR CONTROL USING A SINGLE SWITCH
This simple circuit lets you run a DC motor in clockwise or anti-clockwise
direction and stop it using a single switch. It provides a constant voltage for
proper operation of the motor. The glowing of LED1 through LED3 indicates that
the motor is in stop, forward rotation and reverse conditions, respectively.
more pdf
Bidirectional DC motor speed control using Pulse Width Modulation
The simplest method of implementing microcontroller controlled H-bridge drive of a reversible DC motor is to buy one of many commercial H-bridge IC's availible on the market. These can be purchased separately as an H-Bridge with a separate H-Bridge controller IC, or as an all-in-one IC. Unfortunately, there are several hurdles that sometimes frustrate this approach. Students often find these devices hard to find, as they are apparently in high demand. Secondly, many of these devices have limited current drive ability, such that larger DC motors end up running sluggish or stalling easily. One option is to build your own H-bridge from discrete parts, as shown below.
more
Low-Cost DC Motor Speed Control with CMOS ICs
Two low-cost CMOS ICs manage a 12 VDC, current-limited speed
control circuit for DC brush motors. The circuit design (see
Figure 1) uses PWM (pulse width modulation) to chop the effective
input voltage to the motor. Use of CMOS devices gives the benefits
of low power, minimal heat and improved longevity. The overall
design is simple, inexpensive and reliable, and is useful in applications
such as embedded DC motor control where efficiency,
economy and performance are essential.
more pdf
Digital Speed Control by Anthony Psaila
My design is based around three parts:
1. The controller board. This is a fully digital circuit that takes the 1ms to 2ms pulse from the receiver and converts it into a pwm train at 1Khz. It uses six cmos ics (74hc and 40 series) and a 4Mhz crystal clock. The only other components are one resistor and two capacitors to complete the crystal clock and a capacitor across the supply for smoothing. This was built on a printed board measuring 2 x 2.25 inches using standard components (on the boat there was no shortage of space). If surface mounted devices are used, the lot can be crammed into a much smaller space. The circuit can give a resolution of 128 steps (7bits). Some day I will expand it to have reverse function, but this is better done by a switcher circuit supplied from another channel (my reciever can give 7 channels and I am using only two at present).
more
Speed Controller Circuit
The robot I intend to build will be a 4WD bot with a skid steer system so to do this best I have opted to build 2 a controller system moulded around a 4QD DCI111. (A DCI111 converts radio signals into useable signals) Because of this the inputs on my controllers have to be similar to the 4QD units. The next things to consider are the motors that I will be using. Bosch 750’s seem to be quite popular (so are ford escorts and they are crap) so I will just go ahed and use the many starter motors that I have lying around. This results in
more
DC Motor Control & Interfacing Circuit
A permanent magnet DC motor responds to both voltage and current. The steady state voltage across a motor determines the motor’s running speed, and the current through its armature windings determines the torque. Apply a voltage and the motor will start running in one direction; reverse the polarity and the direction will be reversed. If you apply a load to the motor shaft, it will draw more current, if the power supply does not able to provide enough current, the voltage will drop and the speed of the motor will be reduced. However, if the power supply can maintain voltage while supplying the current, the motor will run at the same speed. In general, you can control the speed by applying the appropriate voltage, while torque is controlled by current. In most cases, DC motors are powered up by using fixed DC power supply, therefore; it is more efficient to use a chopping circuit.
more
PWM D.C. motor drive Circuit
This circuit is a very compact switching regulator for small DC motors. I use it for my small printed circuit board drill (18 Volt, 1.5 Amp), but it is suitable for many other applications (e.g. 12V DC halogen dimmer).
more
Back EMF PM Motor Speed Control Circuit
A 12 V control supply and a TRW BL11, 30 V motor are used; with minor changes other motor and control voltages can be accommodated. For example, a single 24 V rail could supply both control and motor voltages. Motor and control voltages are kept separate here because CMOS logic is used to start, stop, reverse and oscillate the motor with a variable delay between motor reversals.
more
Bidirectional DC Motor Speed Controller
This kit allows controlling the speed of a DC motor in
both the forward and reverse direction. The range of
control is from fully OFF to fully ON in both directions.
This kit overcomes both these problems. The direction and
speed is controlled using a single potentiometer. Turning
the pot in one direction causes the motor to start spinning.
Turning the pot in the other direction causes the motor to
spin in the opposite direction. The center position on the
pot is OFF, forcing the motor to slow and stop before
changing direction.
more pdf
PWM DC Motor Speed Control
The left half of the 556 dual timer IC is used as a fixed frequency square wave oscillator. The oscillator signal is fed into the right half of the 556 which is configured as a variable pulse width one-shot monostable multivibrator (pulse stretcher).
more
DC Motor Controlled with PWM Resources
Here is a description of the driver circuit. It's based on the Microchip AN531 Application Note titled "Remote Positionner". The circuit given in the application Note do not work , so this is a correction of the circuit:
more
DC MOTOR CONTROL USING A SINGLE SWITCH
This simple circuit lets you run a DC motor in clockwise or anti-clockwise
direction and stop it using a single switch. It provides a constant voltage for
proper operation of the motor. The glowing of LED1 through LED3 indicates that
the motor is in stop, forward rotation and reverse conditions, respectively.
more pdf
Bidirectional DC motor speed control using Pulse Width Modulation
The simplest method of implementing microcontroller controlled H-bridge drive of a reversible DC motor is to buy one of many commercial H-bridge IC's availible on the market. These can be purchased separately as an H-Bridge with a separate H-Bridge controller IC, or as an all-in-one IC. Unfortunately, there are several hurdles that sometimes frustrate this approach. Students often find these devices hard to find, as they are apparently in high demand. Secondly, many of these devices have limited current drive ability, such that larger DC motors end up running sluggish or stalling easily. One option is to build your own H-bridge from discrete parts, as shown below.
more
Low-Cost DC Motor Speed Control with CMOS ICs
Two low-cost CMOS ICs manage a 12 VDC, current-limited speed
control circuit for DC brush motors. The circuit design (see
Figure 1) uses PWM (pulse width modulation) to chop the effective
input voltage to the motor. Use of CMOS devices gives the benefits
of low power, minimal heat and improved longevity. The overall
design is simple, inexpensive and reliable, and is useful in applications
such as embedded DC motor control where efficiency,
economy and performance are essential.
more pdf
Digital Speed Control by Anthony Psaila
My design is based around three parts:
1. The controller board. This is a fully digital circuit that takes the 1ms to 2ms pulse from the receiver and converts it into a pwm train at 1Khz. It uses six cmos ics (74hc and 40 series) and a 4Mhz crystal clock. The only other components are one resistor and two capacitors to complete the crystal clock and a capacitor across the supply for smoothing. This was built on a printed board measuring 2 x 2.25 inches using standard components (on the boat there was no shortage of space). If surface mounted devices are used, the lot can be crammed into a much smaller space. The circuit can give a resolution of 128 steps (7bits). Some day I will expand it to have reverse function, but this is better done by a switcher circuit supplied from another channel (my reciever can give 7 channels and I am using only two at present).
more
Friday, July 3, 2009
Why use brushless DC motors (advantages/disadvantages)?
Brushless DC motors are synchronous motors suitable for use as a simple means of controlling permanent drives (e.g. ABS pumps, EHPS pumps, fuel pumps or cooling fans). This type of 3-, 4- or 5-phase brushless DC motor will increasingly replace brushed DC motors. Brushed DC motors require maintenance, e.g. to service coal brushes and commutator. Another major problem with a brushed DC machine is the possibility of brush burnout in the event of an overload or stall condition.
Functional principle of a brushless DC motor
Figure 1 shows a three-phase brushless DC motor with two pole pairs. The rotation of the electrical field (vector) has to be applied twice as fast as the desired mechanical speed of the brushless DC motor. The three coils of the stator are split into two groups of coils (A, B, C and A’, B’, C’). As you can see in Figure 1, coils A and C are energized and coil B is not energized. A 0° to 180° rotation will be shown in detail in section 2.1 to explain the setting of the appropriate switches of the B6 bridge pattern, the appropriate voltages relating to the coils, and the energized coils of the motor with the suitable rotor position between 0° and 180° mechanical.
Brushless DC Motors wiring diagrams
The wiring diagrams for a 3-pole armature (stator) Brushless DC Motors
The wiring diagrams for a 6-pole armature Brushless DC Motors
more
Brushless DC Motors Animation
Brushless DC motors are refered to by many aliases: brushless permanent magnet, permanent magnet ac motors, permanent magnet synchronous motors ect. The confusion arises because a brushless dc motor does not directly operate off a dc voltage source. However, as we shall see, the basic principle of operation is similar to a dc motor.
more
Introduction to Brushless DC Motors
Brushless Motor Construction
DC brushless motors are similar in performance and application to brush-type DC motors. Both have a speed vs. torque curve which is linear or nearly linear. The motors differ, however, in construction and method of commutation. A brush-type permanent magnet DC motor usually consists of an outer permanent magnet field and an inner rotating armature. A mechanical arrangement of commutator bars and brushes switches the current in the armature windings to maintain rotation. A DC brushless motor has a wound stator, a permanent magnet rotor assembly, and internal or external devices to sense rotor position. The sensing devices provide signals for electronically switching (commutating) the stator windings in the proper sequence to maintain rotation of the magnet assembly. The rotor assembly may be internal or external to the stator in a DC brushless motor. The combination of an inner permanent magnet rotor and outer windings offers the advantages of lower rotor inertia and more efficient heat dissipation than DC brush-type construction. The elimination of brushes reduces maintenance, increases life and reliability, and reduces noise and EMI generation.
DC Brushless Motor Control Block Diagram
more
Brushless DC Motor driver circuit
Closed Loop Brushless DC Motor Control With the MC33033 Using the MC33039 driver circuit
The MC33033 is a high performance second generation, limited
feature, monolithic brushless dc motor controller which has evolved
from ON Semiconductor's full featured MC33034 and MC33035
controllers. It contains all of the active functions required for the
implementation of open loop, three or four phase motor control. The
device consists of a rotor position decoder for proper commutation
sequencing, temperature compensated reference capable of supplying
sensor power, frequency programmable sawtooth oscillator, fully
accessible error amplifier, pulse width modulator comparator, three
open collector top drivers, and three high current totem pole bottom
drivers ideally suited for driving power MOSFETs. Unlike its
predecessors, it does not feature separate drive circuit supply and
ground pins, brake input, or fault output signal.
more pdf
THREE-PHASE BRUSHLESS DC MOTOR driver circuit
The L6235 is a DMOS Fully Integrated Three-Phase
Motor Driver with Overcurrent Protection.
Realized in MultiPower-BCD technology, the device
combines isolated DMOS Power Transistors with
CMOS and bipolar circuits on the same chip.
The device includes all the circuitry needed to drive a
three-phase BLDC motor including: a three-phase
DMOS Bridge, a constant off time PWM Current Controller
and the decoding logic for single ended hall
sensors that generates the required sequence for the
power stage.
more pdf
3-Phase Full-Wave PWM Driver for Sensorless brushless Motors driver circuit
The TB6588FG is a three-phase full-wave PWM driver for
sensorless brushless DC (BLDC) motors. It controls rotation speed
by changing the PWM duty cycle, based on the voltage of an
analog control input.
more pdf
Why use brushless DC motors (advantages/disadvantages)?
Brushless DC motors are synchronous motors suitable for use as a simple means of controlling permanent drives (e.g. ABS pumps, EHPS pumps, fuel pumps or cooling fans). This type of 3-, 4- or 5-phase brushless DC motor will increasingly replace brushed DC motors. Brushed DC motors require maintenance, e.g. to service coal brushes and commutator. Another major problem with a brushed DC machine is the possibility of brush burnout in the event of an overload or stall condition.
Functional principle of a brushless DC motor
Figure 1 shows a three-phase brushless DC motor with two pole pairs. The rotation of the electrical field (vector) has to be applied twice as fast as the desired mechanical speed of the brushless DC motor. The three coils of the stator are split into two groups of coils (A, B, C and A’, B’, C’). As you can see in Figure 1, coils A and C are energized and coil B is not energized. A 0° to 180° rotation will be shown in detail in section 2.1 to explain the setting of the appropriate switches of the B6 bridge pattern, the appropriate voltages relating to the coils, and the energized coils of the motor with the suitable rotor position between 0° and 180° mechanical.
Brushless DC Motors wiring diagrams
The wiring diagrams for a 3-pole armature (stator) Brushless DC Motors
The wiring diagrams for a 6-pole armature Brushless DC Motors
more
Brushless DC Motors Animation
Brushless DC motors are refered to by many aliases: brushless permanent magnet, permanent magnet ac motors, permanent magnet synchronous motors ect. The confusion arises because a brushless dc motor does not directly operate off a dc voltage source. However, as we shall see, the basic principle of operation is similar to a dc motor.
more
Introduction to Brushless DC Motors
Brushless Motor Construction
DC brushless motors are similar in performance and application to brush-type DC motors. Both have a speed vs. torque curve which is linear or nearly linear. The motors differ, however, in construction and method of commutation. A brush-type permanent magnet DC motor usually consists of an outer permanent magnet field and an inner rotating armature. A mechanical arrangement of commutator bars and brushes switches the current in the armature windings to maintain rotation. A DC brushless motor has a wound stator, a permanent magnet rotor assembly, and internal or external devices to sense rotor position. The sensing devices provide signals for electronically switching (commutating) the stator windings in the proper sequence to maintain rotation of the magnet assembly. The rotor assembly may be internal or external to the stator in a DC brushless motor. The combination of an inner permanent magnet rotor and outer windings offers the advantages of lower rotor inertia and more efficient heat dissipation than DC brush-type construction. The elimination of brushes reduces maintenance, increases life and reliability, and reduces noise and EMI generation.
DC Brushless Motor Control Block Diagram
more
Brushless DC Motor driver circuit
Closed Loop Brushless DC Motor Control With the MC33033 Using the MC33039 driver circuit
The MC33033 is a high performance second generation, limited
feature, monolithic brushless dc motor controller which has evolved
from ON Semiconductor's full featured MC33034 and MC33035
controllers. It contains all of the active functions required for the
implementation of open loop, three or four phase motor control. The
device consists of a rotor position decoder for proper commutation
sequencing, temperature compensated reference capable of supplying
sensor power, frequency programmable sawtooth oscillator, fully
accessible error amplifier, pulse width modulator comparator, three
open collector top drivers, and three high current totem pole bottom
drivers ideally suited for driving power MOSFETs. Unlike its
predecessors, it does not feature separate drive circuit supply and
ground pins, brake input, or fault output signal.
more pdf
THREE-PHASE BRUSHLESS DC MOTOR driver circuit
The L6235 is a DMOS Fully Integrated Three-Phase
Motor Driver with Overcurrent Protection.
Realized in MultiPower-BCD technology, the device
combines isolated DMOS Power Transistors with
CMOS and bipolar circuits on the same chip.
The device includes all the circuitry needed to drive a
three-phase BLDC motor including: a three-phase
DMOS Bridge, a constant off time PWM Current Controller
and the decoding logic for single ended hall
sensors that generates the required sequence for the
power stage.
more pdf
3-Phase Full-Wave PWM Driver for Sensorless brushless Motors driver circuit
The TB6588FG is a three-phase full-wave PWM driver for
sensorless brushless DC (BLDC) motors. It controls rotation speed
by changing the PWM duty cycle, based on the voltage of an
analog control input.
more pdf
Saturday, June 20, 2009
Microstepping Stepper Motor Data
Microstepping of Stepping Motors
Introduction
Microstepping serves two purposes. First, it allows a stepping motor to stop and hold a position between the full or half-step positions, second, it largely eliminates the jerky character of low speed stepping motor operation and the noise at intermediate speeds, and third, it reduces problems with resonance.
Although some microstepping controllers offer hundreds of intermediate positions between steps, it is worth noting that microstepping does not generally offer great precision, both because of linearity problems and because of the effects of static friction.
1 Sine-Cosine Microstepping
2 Limits of Microstepping
- Detent Effects
- Quantization
3 Typical Control Circuits
- Practical Examples
http://www.cs.uiowa.edu/~jones/step/micro.html
Microstepping Stepper Motor Driver Kit
Basic design
It is a unipolar (or 5-wire type) driver. The motor must have
5 or 6 wires (or 8), as 4-wire motors are only for bipolar
and 4-WIRE MOTORS WILL NOT WORK WITH THIS BOARD.
The constant current system is crude but simple, it relies on
setting the base of the main transistors at a "set" level, then
this causes a "set" voltage across the sense resistor Rs, ie
maintains constant current. It does get some temp drift with
large currents, but it's simple and accurate enough with the
resistor values i've tested. It actually works quite well!
The brain has control of which of the 4 transistors are ON,
and sets 3 possible current levels, enough to do 6th stepping
and give 1200 steps/rev with hardware alone. The software I
have provided also will do pwm and give 18th stepping, which
is 3600 steps/rev, almost stepless operation.
The PIC has plenty of left over rom if you need to do motion
control or use the board as the complete brains and driver for
an entire machine. Up to 9 PIC in/out pins can be allocated to
the board.
http://www.piclist.com/tecHREF/io/stepper/linistep/lini_wks.htm
Micro-step driver
This circuit allows to connect a bipolar step motor to a personal computer through the parallel port. The circuit is, for safety reasons, optically isolated from the PC and it allows to manage motors up to 3A for phase. Moreover the digital interface allows to connect up to six motors to a single PC parallel port.
The more interesting aspect of this circuit is its ability to implement the microstep technique and to multiply up to 64 times the motor real steps number. As an example, a 200 steps motor could behave like "a virtual" 12.800 steps motor. This function is particularly useful when the spin speed is very low, in the order of fractions of rpm.
http://www.vincenzov.net/eng/design/microstep.htm
L6208 FULLY INTEGRATED TWO PHASE STEPPER MOTOR DRIVER
Modern motion control applications need more flexibility that can be addressed only with specialized IC products. The L6208 is a fully integrated stepper motor driver IC specifically developed to drive a wide range
of two phase (bipolar) stepper motors. This IC is a one-chip cost effective solution that includes several unique circuit design features. These features, including a decoding logic that can generate three different stepping sequences, allow the device to be used in many applications including microstepping. The principal aim of this development project was to produce an easy to use, fully protected power IC. In addition several key functions such as protection circuit and PWM current control drastically reduce external components count to meet requirements for many different applications.
Microstepping Stepper Motor Driver Circuit
http://www.st.com/stonline/books/pdf/docs/8607.pdf
MICROSTEPPING STEPPER MOTOR DRIVE
USING PEAK DETECTING CURRENT CONTROL
Stepper motors are very well suited for positioning applications since they can achieve very good positional accuracy without complicated feedback loops associated with servo systems. However their resolution, when driven in the conventional full or half step modes of operation, is limited by the configuration of the motor. Many designers today are seeking alternatives to increase the resolution of the stepper motor drives. This application note will
discuss implementation of microstepping drives using peak detecting current control where the sense resistor is connected between the bottom of the bridge and ground. Examples show the implementation of microstepping drives with several currently available chips and chip sets.
INTRODUCTION
Microstepping a stepper motor may be used to achieve one or both of two objectives; 1) increase the position resolution or 2) achieve smoother operation of the motor. In either case the basic theory of operation is the same. The simplified model of a stepper motor is a permanent magnet rotor and two coils on the stator separated by 90 degrees, as shown in Figure 1. In classical full step operation an equal current is delivered to each of the coils and the rotor will align itself with the resulting magnetic vector along one of the 45 degree axis. To step the motor, the current in one of the two coils is reversed and the rotor will rotate 90 degrees. The complete full step sequence is shown in figure 2. Half step drive, where the current in the coil is turned off for one step period before being turned on in the opposite direction, has been used to double the step resolution of a motor. In either full and half step drive,
the motor can be positioned only at one of the 4 (8 for half step) defined positions.[4][5] Therefore,
the number of steps per electrical revolution and the number of poles on the motor determine the resolution of the motor. Typical motors are designed for 1.8 degree steps (200 steps per revolution) or 7.5 degree steps (48 steps per revolution). The resolution may be doubled to 0.9 or 3.75 degrees by driving the motor in half step. Further increasing the resolution requires positioning the rotor at positions between the full step and half step positions.
Example alignment of microsteping
http://www.st.com/stonline/books/pdf/docs/8700.pdf
Precision Microstepping Driver Circuit
Microstepping Stepper Motor Driver Project
Functional description
The circuit can be divided into three functional blocks, Microprocessor simulation logic, micro-stepping controller and stepper motor driver.
A. Micro-stepping simulation.
This block send the control signals normally sent by a microprocessor to the micro-stepping controller, the inputs to the block are the 5 Dip-switches and the clock pulse from pin1 of J2. During normal operation the current level in one of the motor windings is updates at every step pulse (single pulse programming). These mean two step pulses are required to update both winding currents and make the motor turn. Operating the dip-switched S1-6 can change the direction of the motor rotation
http://home.att.net/~wzmicro/3960drv.html
