- Glossary of terms:
-
- Acceleration
- A change in velocity as a function of time. Acceleration usually
refers to increasing velocity, and deceleration to decreasing
velocity.
-
- Accuracy
- A measure of the difference between expected position and actual
position of a motor or mechanical system. Motor accuracy is usually
specified as an angle representing the maximum deviation from
expected position.
-
- Ambient temperature
- The temperature of the cooling medium, usually air, immediately
surrounding the motor or another device.
-
- Angular accuracy
- The measure of shaft positioning accuracy on a servo or stepping
motor.
-
- Back EMF
- The voltage generated when a permanent magnet motor is rotated.
This voltage is proportional to motor speed and is present regardless
of whether the motor winding(s) are energized or de-energized.
-
- Bipolar chopper driver
- A class of step motor driver which uses a switch mode (chopper)
technique to control motor current and polarity. Bipolar indicates
the capability of providing motor phase current of either polarity
(+ or -).
-
- Breakaway torque
- The torque required to start a machine in motion. Almost always
greater than the running torque.
-
- Brushless motor
- Class of motors that operate using electronic commutation of phase
currents, rather than electromechanical (brush-type) commutation.
Brushless motors typically have a permanent magnet rotor and a wound
stator.
- A standard NEMA mounting design, where the mounting holes in the
face are threaded to receive the mating mount.
-
- Class B insulation
- A NEMA insulation specification. Class B insulation is rated to an
operating (internal) temperature of 130°C.
-
- Class F insulation
- A NEMA insulation specification. Class F insulation is rated to an
operating (internal) temperature of 155°C
-
- Class H insulation
- A NEMA insulation specification. Class H insulation is rated to an
operating (internal) temperature of 180°C.
-
- Closed loop
- A broadly applied term, relating to any system in which the output
is measured and compared to the input. The output is then adjusted
to reach the desired condition. In motion control, the term
typically describes a system utilizing a velocity and/or position
transducer to generate correction signals in relation to desired
parameters.
-
- Cogging (Cogging torque)
- A term used to describe non-uniform angular velocity. Cogging
appears as a jerkiness, especially at low speeds.
-
- Commutation
- 1. A term which refers to the action of steering currents or
voltages to the proper motor phases so as to produce optimum motor
torque. In brush type motors, commutation is done electromechanically
via the brushes and commutator. In Brushless motors, commutation is
done by the switching electronics using rotor position information
obtained by Hall sensors, a Tachsyn, or a Resolver.
- 2. Commutation of step motors is normally done open loop. Feedback
from the motor is not required to hold rotor position precisely.
-
- Continuous rated current (ICR) (Amperes)
- The maximum allowable continuous current a motor can handle
without exceeding the motor temperature limits
-
- Continuous rated torque (TCR) (lb-in.)
- The maximum allowable continuous torque a motor can handle without
exceeding the motor temperature limits
-
- Continuous stall current (ICS) (Amperes)
- Amount of current applied to a motor (at locked rotor conditions),
which results in rated temperature rise. Refer also to definition of
"Continuous stall torque"
-
- Continuous stall torque (TCS)
(lb-in.)
- The amount of torque at zero speed, which a motor can continuously
deliver without exceeding its thermal rating. Determined by applying
DC current through two windings with rotor locked, while monitoring
temperature. Specified with motor windings at maximum rated
temperature, with motor in 25 degrees C ambient, mounted to a heat
sink. Refer to individual specs for heat sink size.
-
- Controller
- A term describing a functional block containing an amplifier,
power supplies, and possibly position-control electronics for
operating a servomotor or step motor.
-
- Current at peak torque (IPK)
(Amperes)
- The amount of input current required to develop "peak
torque". This is often outside the linear torque/current
relationship.
-
- Current, Rated
- The maximum allowable continuous current a motor can handle
without exceeding motor temperature limits.
-
- D-flange mounting C-face mounting
- This type of mount has clearance holes on the flange, and the
mounting bolts stick out through the flange from the motor side.
This mount is common in cases where the motor is integral to the
machine.
-
- Demag current
- The current level at which the motor magnets will start to be
demagnetized. This is an irreversible effect, which will alter the
motor characteristics and degrade performance. Also known as peak
current.
-
- Detent torque
- The maximum torque that can be applied to an unenergized step
motor without causing continuous rotating motion.
-
- DPBV - Dripproof Blower Ventilated
- Type of motor cooled by blowing air through the inside of the
motor using an attached blower.
-
- Drive
- An electronic device that controls torque, speed and/or position
of an AC or Brushless motor. Typically a feedback device is mounted
on the motor for closed-loop control of current, velocity and
position.
-
- Driver
- Electronics which convert step and direction inputs to high power
currents and voltages to drive a step motor. The step motor driver
is analogous to the servomotor amplifier's logic.
-
- Duty cycle
- For a repetitive cycle, the ratio of on time to total cycle time.
- Duty cycle (%) = [On time / (On time + Off time)] x 100%
-
- Dynamic braking
- A passive technique for stopping a permanent magnet brush or Brushless
motor. The motor windings are shorted together through a
resistor which results in motor braking with an exponential decrease
in speed.
-
- Efficiency
- The ratio of power output to power input.
-
- Electrical time constant (te)
(Seconds)
- The time required for current to reach 63.2% of its final value
for a fixed voltage level. Can be calculated from the relationship te=L/R
where L is inductance (henries) and R is resistance (ohms).
-
- Encoder
- A feedback device which converts mechanical motion into electronic
signals. The most commonly used, rotary encoders, output digital
pulses corresponding to incremental angular motion. For example, a
1000-line encoder produces 1000 pulses every mechanical revolution.
The encoder consists of a glass or metal wheel with alternating
transparent and opaque stripes, detected by optical sensors to
produce the digital outputs.
-
- Feedback
- A signal which is transferred from the output back to the input
for use in a closed loop system.
-
- Ferrite
- A type of permanent magnet consisting of ceramic compounds made up
of oxides of iron, barium and strontium.
-
- Form factor
- The ratio of RMS current to average current. This number is a
measure of the current ripple in a SCR or other switch-mode type of
drive. Since motor heating is a function of RMS current while motor
torque is a function of average current, a form factor greater than
1.00 means some fraction of motor current is producing heat but not
torque.
-
- Four quadrant
- Refers to a motion system which can operate in all four quadrants;
i.e., velocity in either direction and torque in either direction.
This means that the motor can accelerate, run, and decelerate in
either direction.
-
- Friction
- A resistance to motion caused by contact with a surface. Friction
can be constant with varying speed (Coulomb friction) or
proportional to speed (viscous friction).
-
- Hall sensor
- A feedback device which is used in a Brushless servo system to
provide information for the amplifier to electronically commutate
the motor. The device uses a magnetized wheel and hall effect
sensors to generate the commutation signals.
-
- Holding torque
- Sometimes called static torque, holding torque specifies the
maximum external torque that can be applied to a stopped, energized
motor without causing the rotor to rotate. Generally used as a
figure of merit when comparing motors.
-
- Horsepower
- An index of the amount of work a machine or motor can perform. One
horsepower is equal to 746 watts. Since power is equal to torque
multiplied by speed, horsepower is a measure of a motor's torque and
speed capability; e.g., a 1 HP motor will produce 36 lb-in. at 1,750
rpm.
- Formula:
- HP = Torque (lb-in.) x Speed (RPM)/63,025
- or
- HP = Torque (lb-ft.) x Speed (RPM)/5,252
- or
- HP = Volts x Amps x Efficiency/746
-
- Hybrid step motor
- A motor designed to move in discrete increments of steps. The
motor has a permanent magnet rotor and a wound stator. Such motors
are Brushless. Phase currents are commutated as a function of time
to produce motion.
-
- Idle current reduction
- A step motor driver feature that reduce the phase current to the
motor when no motor motion is commanded (idle condition) for a
specified period of time. Idle current reduction reduces motor
heating and allows high machine throughputs from a given motor.
-
- Indexer
- Electronics which convert high level motion commands from a host
computer, PLC or operator panel into step and direction pulse
streams for use by the step motor driver. Indexers can be broadly
divided into two classes. A preset indexer typically accepts
distance, velocity and ramp time inputs only. The more sophisticated
programmable indexer is capable of complex motion control and
includes program memory.
-
- Inductance (L) (mH - millihenries
line-to-line)
- The electrical equivalent to mechanical inertia; that is, the
property of a circuit, which has a tendency to resist current flow
when no current is flowing, and when current is flowing has a
tendency to maintain that current flow. Powertec measures
inductance (line-to-line) with a bridge at 1000 Hz and with the rotor
positioned so the back-EMF waveform is at the peak of the
sinusoid.
-
- Inductance (mutual)
- Mutual inductance is the property that exists between two current
carrying conductors or coils when magnetic lines of force from one
link with those of the other.
-
- Inertia
- The property of an object to resist change in velocity unless
acted upon by an outside force. Higher inertia objects require
larger torques to accelerate and decelerate. Inertia is dependent
upon the mass and shape of the object.
-
- Inertial match
- For most efficient operation, the system coupling ratio should be
selected so that the reflected inertia of the load is equal to the
rotor inertia of the motor.
-
- Insulation Class
- The rating assigned to the maximum temperature capability of the
insulating components in a motor or other piece of equipment.
-
- Mechanical time constant (tm) (Seconds)
- In a simple first order system, the time required for the motor's
speed to attain 63.2% of its final value for a fixed voltage level.
Can be calculated from:
- where:
- J is inertia in lb-in./s2
- R is resistance in ohms
- KT is torque constant in lb-in./amp.
- 8.87 is a conversion factor
- tM is calculated in seconds
-
- Microstepping
- An electronic technique for increasing a step motor's position
resolution and velocity smoothness by appropriately scaling the phase
currents. Microstepping is also a technique used to reduce or
eliminate the effects of system resonance at low speeds.
-
- Mid-range instability
- A phenomenon in which a step motor can fall out of synchronism due
to a loss of torque at mid-range speeds. The torque loss is due to
the interaction of the motor's electrical characteristics and the
driver's electronics. Some drivers have circuitry to eliminate or
reduce the effects of mid-range instability.
-
- NEMA - National Electrical Manufacturer's
Association
- Acronym for an organization which sets standards for motors and
other industrial electrical equipment.
-
- Neodymium iron boron
- A type of rare-earth permanent magnet material.
-
- NTC - Negative Temperature Coefficient
- A negative temperature coefficient thermistor is used to detect
and protect a motor winding from exceeding its maximum temperature
rating. Resistance of the device decreases with an increase in
temperature.
-
- Open-loop
- A system in which there is no feedback. Motor motion is expected
to faithfully follow the input command. Stepping motor systems are
an example of open-loop control.
-
- Overload capacity
- The ability of a drive to withstand currents above its continuous
rating. It is defined by NEMA as 150% of the rated full-load current
for "standard industrial DC motors" for one minute.
-
- Peak torque (Tpk) (lb-in.)
- The maximum torque a Brushless motor can deliver for short periods
of time. Operating PacTorq motors above the maximum torque value can
cause demagnetization of the rare-earth magnets. This is an
irreversible effect that will alter the motor characteristics and
degrade performance. This is also known as peak current.
-
- Not to be confused with system peak torque, which is often
determined by amplifier peak current limitations, where peak current
is typically two times continuous current.
-
- Poles
- Refers to the number of magnetic poles arranged on the rotor of
the Brushless motor. Unlike an AC motor, the number of poles has no
direct relationship to the base speed of the motor.
-
- Power
- 1. The rate at which work is done. In motion control, power is
equal to torque multiplied by speed.
- 2. The rate of doing work or expending energy. It may be written
as: Power (watts) = force x distance/time. Expressed in electrical
terms it is voltage x current = power (watts)
-
- Power factor
- Ratio of true power (kW) to apparent power (kVA).
-
- PTC - Positive Temperature Coefficient
- A positive temperature coefficient thermistor is used to detect
and protect a motor winding from exceeding its maximum temperature
rating. Resistance of the device increases with an increase in
temperature.
-
- Pull-out torque
- The maximum friction load, at a particular inertial load, that can
be applied to the shaft of a synchronous motor (running at constant
speed) and not cause it to lose synchronism.
-
- Pulse rate
- The frequency of the step pulses applied to a step motor driver.
The pulse rate, multiplied by the resolution of the motor/driver
combination (in steps per revolution), yields the rotational speed
in revolutions per second.
-
- Pulse Width Modulation (PWM)
- 1. A PWM controller (amplifier) switches DC supply voltage on and
off at fixed frequencies. The length of the on/off interval or
voltage waveform is variable.
- 2. Pulse width modulation (PWM), describes a switch-mode (as
opposed to linear) control technique used in amplifiers and drivers
to control motor voltage and current. PWM offers greatly improved
efficiency compared to linear techniques.
-
- Regeneration
- The action during motor braking, in which the motor acts as a
generator and takes kinetic energy from the load, converts it to
electrical energy, and returns it to the amplifier.
-
- Repeatability
- The degree to which a parameter such as position or velocity can
be duplicated.
-
- Resistance, Hot (RH)(Ohms
line-to-line)
- The motor's terminal resistance value specified at the hot winding
temperature, which is at the motor's maximum rated temperature.
-
- Resolution
- The smallest increment into which a parameter can be broken down.
For example, a 1000 line encoder has a resolution of 1/1000 of a
revolution.
-
- Resolver
- An electromagnetic feedback device which converts angular shaft
position into analog signals. These signals can be processed in
various ways, such as with an RDC (resolver-to-digital converter) to
produce digital position information. There are two basic types of
resolvers; transmitter and receiver. A transmitter-type is designed
for rotor primary excitation and stator secondary outputs. Position
is determined by the ratio of the sine output amplitude to cosine
output amplitude. A receiver-type is designed for stator primary
excitations and rotor secondary output. Position is determined by the
phase shift between the rotor output signal and one of the primary
excitation signals.
-
- Resonance
- Oscillatory behavior caused by mechanical limitations.
-
- Restart torque
- The maximum friction load, at a particular inertial load, that can
be applied to the shaft of a synchronous motor without causing it to
lose synchronism when accelerating to a constant speed from
standstill.
-
- Ringing
- Oscillation of a system following a sudden change in state.
-
- RMS Current - Root Mean Square Current
- In an intermittent duty cycle application, the RMS current is
equal to the value of steady state current which would produce the
equivalent motor heating over a period of time.
-
- RMS Torque - Root Mean Square
Torque.
- In an intermittent duty cycle application, the RMS torque is equal
to the value of steady state torque which would produce the
equivalent motor heating over a period of time.
-
- Rotor
- The moving part of the motor, consisting of the shaft and magnets.
These magnets are analogous to the field winding of a brush-type DC
motor.
-
- Settling time
- The time required for a parameter to stop oscillating or ringing
and reach its final value.
-
- Shock loading
- A load that produces extremely high peak torques for very short
durations. This type of load is associated with conveyorized
grinding, crushing and separation processes.
-
- Speed
- Describes the linear or rotational velocity of a motor or other
object in motion.
-
- Stall Torque
- The amount of torque developed with voltage applied and shaft
locked, or not rotating. Also known as locked-rotor torque.
-
- Stator
- The non-moving part of the motor. Specifically, it is the iron
core with the wire winding in it that is pressed into the frame
shell. The winding pattern determines the voltage constant of the
motor.
-
- Step angle
- The angular distance the shaft rotates upon receipt of a single
step command.
-
- Stiffness
- The ability to resist movement induced by an applied torque.
Stiffness is often specified as a torque displacement curve,
indicating the amount a motor shaft will rotate upon application of
a known external force when stopped.
-
- Synchronism
- A motor rotating at a speed corresponding correctly to the applied
step pulse frequency is said to be in synchronism. Load torques in
excess of the motor's capacity (rated torque) will cause a loss of
synchronism. This condition is not damaging to a step motor.
-
- TENV - Totally Enclosed Non-Ventilated
- Acronym describing a type of motor enclosure, which has no outside
air going into it. It is cooled only by convection to the frame,
which is usually finned.
-
- Thermal protection
- A thermal sensing device mounted to the motor to protect it from
overheating. This is accomplished by disconnecting the motor phases
from the drive in an over temperature condition.
-
- Thermal resistance (Rth) (°C/watt)
- An indication of how effectively a unit rids itself of heat; a
measure of temperature rise per watts lost. In Powertec Indusrtrial
Motors literature, it is the specified value from the motor windings
to the ambient, under locked rotor conditions.
-
- Thermal time constant (tth)
(minutes)
- The time required for a motor to attain 63.2% of its final
temperature for a fixed power input.
-
- Thermostat
- A temperature sensitive pilot duty device mounted on the interior
of the motor to protect it from overheating.
-
- Torque
- A measure of angular force which produces rotational motion. This
force is defined by a linear force multiplied by a radius; e.g.
lb-in. Torque is an important parameter of any motion control
system. Formula: Torque (lb-ft.) = 5,250 x HP/RPM
-
- Torque Constant (KT = lb-ft./A)
- An expression of the relationship between input current and output
torque. For each ampere of current, a fixed amount of torque is
produced.
-
- Torque-to-inertia ratio
- Defined as the motor's holding torque divided by the inertia of
its rotor. The higher the ratio, the higher a motor's maximum
acceleration capability will be.
-
- Unipolar driver
- A step motor driver configuration that uses a unipolar power
supply and is capable of driving phase current in only one
direction. The motor phase winding must be center tapped (6 or 8
lead) to operate with a unipolar driver. The center tap is used
instead of providing the current reversal of a bipolar driver.
-
- Velocity
- The change in position as a function of time. Velocity has both a
magnitude and sign.
-
- Viscous Damping (KDV) (lb-in./kRPM)
- Inherent losses are present in all motors which result in lower
torque delivered at the output shaft than developed at the rotor.
Losses which are proportional to speed (i.e. speed dependent terms
such as windage, friction, eddy current) are related through the
motor's "viscous damping" constant, measured as the slope
of the damping curve.
-
- Voltage constant (KE) (V/kRPM peak,
line-to-line)
- May also be termed back-EMF constant. When a motor is operated, it
generates a voltage proportional to speed, but opposing the applied
voltage. The shape of the voltage waveform depends upon the specific
motor design. For example, in a Brushless motor, the wave shape may
be trapezoidal or sinusoidal in nature. All Powertec Brushless motor
designs have a sinusoidal voltage constant. For a sine waveform, the
voltage constant can be measured from line-to-neutral or line-to-line
and expressed as a peak value or "RMS" value.
-
- Watt
- One horsepower equals 746 watts.
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