| AC
|
Alternating Current.
(EU mains at 50 Hz: typically 230 Volt single phase or 400 Volt
3 phase; USA mains at 60Hz: 115 Volt single phase, 230 Volt
dual phase and many 3 phase voltages). |
| Bipolar |
Stepper motor: The windings
are internally connected (4 leadwires) or externally connected
(6 or 8 leadwires), in series or in parallel, to form 2 phases;
both phases (4 windings) are energised at the same time for
highest torque output. |
| Brush/Brushgear
|
A solid block conductor, usually
made of carbon, that passes current from the power supply onto
a rotating cylindrical/round metal commutator to energise the
motor windings.
(the term "brushes" derives from earlier times when
rods of copper wire were packed together like the hairs on a
broom). |
| Brushless
|
Non-contact devices indicate the
rotor's position to energise the appropriate winding (similar
to a car's electronic ignition if it uses solid state components
instead of a rotor arm contact and copper posts). |
| Commutator |
A cylinder/disc of alternating metallic
and insulated segments connected to the rotor. |
| DC |
Direct Current (power supply is
from a battery or a rectified AC source). |
| FHP |
Fractional Horse Power (1hp = 746
Watts). |
| Flameproof
|
Designed to meet levels of approvals
by internationally recognised bodies for hazardous conditions
in areas that have a risk of gases/vapours detrimental to the
safe operation of the installation. |
| Harmonic gear |
Ultra low backlash gear technology
with medium-high reduction ratios for accurate bi-directional
repeatability, high efficiency and power to weight. |
| Helical gear |
Gear stages have skewed teeth for
lower acoustic noise and higher torque transfer than found with
spur gearing. |
| Hybrid |
A combination of permanent magnet
and variable reluctance technologies for high speed and high
torque.
Typically, the step size is 1.8° (200 full steps/rev) with 4
windings. |
| IEC |
International Electrotechnical
Commission (European standards organisation). |
| NEMA |
National Electrical Manufacturers
Association (US standards organisation).
|
| NEMA frame
|
The body diameter of a model or
series in tenths of an inch, irrespective of the front flange
dimensions. Stepper motor: Popular frames are from size
17 to 42, though smaller and larger than this are possible.
AC and DC motors: The height from the base to the shaft
centre in tenths of an inch. Size 56 and above are normally
interchangeable among manufacturers.
NEMA sizes allow easier interchange of fixings with motor technologies
as, for example, from a NEMA DC brush motor to a NEMA stepper
or to a NEMA brushless motor. |
| Planetary gear |
Compact and rugged staple of medium
technology applications with in-line output shaft, normally
offering high efficiency and high torque. The load is transmitted
through planet gears that mesh between an internal gear cut
in the housing and a central sun gear. |
| Spur gear |
Lends itself to very high ratios
in a large variety of slim case designs. Each stage consists
of a gearwheel with a smaller gearwheel (pinion) at its centre.
Multiple output shafts at different synchronised speeds are
easily achieved for timing applications. |
| Steps/rev |
Stepper motor: The number
of full steps needed to complete a revolution of the motor shaft.
Hybrid steppers have between 8 and 500 full steps per revolution.
Half- and micro- (mini-) stepping drivers divide the motor's
full step into discrete fractions for finer positioning, smoother
rotation, reduced torque ripple and attenuation of system resonance.
|
| Torque |
A rotating force. Various technologies
use special definitions, some of which are listed below:
Breakdown (Shunt wound motor) - the maximum attainable
without a large, sudden reduction in speed.
Detent (Stepper motor) - internal magnetic attraction;
4th harmonic of the full-step torque. Without power applied,
it can be measured as a torque that resists rotation of the
rotor by external force. Typical value is 5 percent of the holding
torque.
Holding (Stepper motor) - with rated current in 2 or
4 windings at zero speed.
For bipolar connections it is with 2 phases (1 phase = 2 windings)
energised and for unipolar connections it is with 2 windings
(1 winding = 1 phase) energised.
Peak - usually the torque above the rated value that is available
for a specified time or with additional cooling and heat-sinking. Sometimes,
it is the maximum achievable without detriment to the motor's
commutator, brushgear, windings or magnet system.
Pull-in (Stepper motor) - the maximum torques, over a
range of speeds, which the motor can start and stop within without
losing steps under defined conditions (load inertia, power supply,
drive mode, etc).
Pull-in (Synchronous motor) - the maximum torque that
can accelerate a defined load into synchronism at rated voltage
and frequency.
|
| Unipolar |
Stepper motor: Connects 8
leadwires as 4 phases, but with only 1 or 2 phases (1 or 2 windings)
energised at any one time. |
| Winding |
Copper coils within a motor that
carry current to produce a magnetic field. Depending on the
motor technology, a winding is situated in the stator, in the
rotor or in both. |
| Worm gear |
Right angle output shafts with self-locking
capability in medium to high ratios; the worm is located concentric
to and in line with the motor shaft; the wheel mates with the
worm with the output shaft at its centre. Ratios up to about
100:1 with a single worm/wheel stage and many thousands :1 with
a second worm/wheel stage. |
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