is a device that provides or facilitates accurate control of a motor,
which is an essential ingredient of any motion control application. A
is simply a
motor controller in integrated circuit form.
There are many types of motors used in various industries today,
all of which can now be controlled by one type of motor controller IC or
another. Commonly used
types of motors include the DC motor, the stepper motor, and the
servo motor, each of which has many variants of its own.
say, the type of input required and output provided by an IC motor
controller depends on the type of motor it controls. It must be
noted, however, that some advanced motor controller IC's can control
several different types of motors. Below are brief descriptions
of what motor controller IC's generally offer.
DC Motor Controllers
There are two
major types of DC motor - the common DC motor with brushes, and the
brushless DC motor. Both types has a non-moving source of magnetic
fields, known as a
and a rotating source of magnetic fields, known as the
The interaction of the magnetic fields from the stator and the rotor is
what makes the motor shaft turn.
which is operated
simply by applying a DC voltage across its terminals, has a
'permanent magnet' stator and an 'electromagnet' rotor. It uses its
brushes to deliver commutating current from the motor's external terminals to the
moving rotor coils inside. A
brushless DC motor, on the other hand, has a 'permanent magnet' rotor
and an 'electromagnet' stator. It requires a more complex form of energization to operate - proper sequencing of the
delivery of commutating currents to its stator coils. Brushless DC motors are
not subject to the arcing caused by brushes, and therefore have a longer
motors are not widely used in precision motion control application
because they are difficult to control. Brushless DC motors are more
widely used, which is why many motor controller IC's for DC motors cater
to the brushless type.
brushless DC motor controller IC is equipped with a control circuit and
a driver circuit. The
which is the 'brain' of the controller IC, generates a control output
based on some form of input. For instance, it may receive feedback about
the state of the motor, usually in the form of input data based on Hall
Effect, which it decodes. The logic circuit then applies a built-in
commutation logic that interprets the decoded feedback information and
outputs the appropriate
to the driver circuit.
driver circuit, which
translates the logic circuit commands into motor-useable currents,
typically consists of a set of integrated power drivers that supply the
correct sequence of currents to the brushless DC motor. It may
also have a built-in pulse width modulation (PWM) circuit that varies
the amounts of DC currents delivered to the motor to control its torque and
DC motor controller IC's can
control DC motors over a wide range of motor supply voltages (up to 50
V) and motor winding currents (several amperes). They may also
provide specialized outputs such as tachometer readings for use in speed
Stepper Motor Controllers
is a motor that converts digital pulses into mechanical shaft rotation.
These pulses control the rotation of the shaft in small angular 'steps',
hence the name 'stepper motor'. Stepper motors come in a wide
i.e., from 90 degrees per step to as low as 0.72 degrees per step. The speed and
torque of a stepper motor are determined by the amount of current
through its windings. Stepper
motors are simple, low-cost, yet highly reliable motors that can operate
in almost any environment.
motor rotates in discrete 'steps' because its movement is achieved by
'teeth' of the rotor with certain poles of the stator (depending on
which windings are energized and which are not) at any given time. As
such, there are only specific
at which the rotor can 'rest.'
Every time a new set of pulses is delivered, the rotor
rotates to the next 'equilibrium point', and its
angular position with respect to the stator is locked in place until a
new set of pulses arrives.
in which a stepper motor can be operated, namely, full stepping, half
stepping, and micro-stepping. Every step taken under full stepping
mode results in a rotation equal to 100% of the angular displacement
specified for a single step. Half-stepping results in only 50% of
this, so it would take twice as many steps under the half-stepping mode as
what it would take under the full-stepping mode to cover the same angular
displacement. Micro-stepping further reduces the angular
displacement equivalent to a single step of the motor.
must be able to handle the generation and conditioning of pulses needed
to operate the stepper motor easily even in complex applications. To
accomplish this, a typical stepper motor controller IC consists of three
basic elements: 1) an
which generates low level signals that correspond to step pulses and
direction signals (collectively referred to as 'indexer commands')
needed to control the stepper motor; 2) a
which translate the indexer commands into power that energizes the
appropriate windings of the stepper motor; and 3) an
that would allow it to be controlled more conveniently by a computer,
PLC, or microcontroller.
designers take into consideration when choosing a stepper motor
controller IC include the following: 1) the ability to put a stepper
motor in continuous 'run' mode at various speed profiles, or in 'step'
mode with precision control; 2) directional control; 3) available
stepping modes for resolution control; 4) programmability; 5)
specialized I/O controls; 6) feedback mechanisms about the state of the
stepper motor; 7) effective and efficient energization of the
stepper motor; 8) industry-standard user interfaces; and 9) ease of
Servo Motor Controllers
servo motor is a
motor whose angular displacement at any one time is determined by a
coded signal, which is usually the width of the pulse applied to its
control terminal. It is operated in a
i.e., it requires some form of analog feedback (usually provided by a
potentiometer) to let it know the current rotor position. Thus,
the repeatability of a servo motor's positioning depends greatly on the
stability of the potentiometer and other components used in the feedback
circuit. Since a stepper motor operates without feedback, a servo motor
is a better choice than a stepper motor if monitoring of the rotor
position at any given time is important.
Since a servo
motor operates on the widths of the control pulses it receives, a
must be capable of
pulse width modulation (PWM).
The servo motor expects to see a pulse regularly, say, every 20
milliseconds. The pulse width influences the amount of power delivered
to the motor and, therefore, its angular displacement as well, i.e., the
longer the pulse, the larger the rotation will be.
servo motor controller IC's in the market include : 1) ability to
support multiple motors; 2) velocity and trapezoidal profiling; 3)
directional control; 4) programmability; 5) specialized I/O controls; 6)
stable feedback mechanisms; 7) overcurrent and power failure
protection; 8) industry-standard user interfaces; and 9) ease of use.
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