Linear motor applications: Ironcore versus Ironless Solutions
Herve Stampfli
Abstract:
Linear servo motors have now established themselves as the drive technology of choice
for high performance motion control applications. From automation to semiconductor
and electronics industries, the constantly increasing requirements for throughput
improvement, flexibility and dynamics in the machines has led the manufacturers to opt
for the “direct drive” approach.
In the marketplace today, there are two predominant types of brushless linear motors that
are widely utilized: the ironless, or “U-channel” motor, and the iron core or “single sided
magnet” type. While they are both linear servo-motors, they have vastly different
performance characteristics. That makes the different types suitable for certain types of
applications and unsuitable for others.
While the general knowledge of engineers regarding the advantages of linear motors is
advancing rapidly, the differences between the main motor types are not well understood.
Further to the point, there are many misconceptions as to the advantages and drawbacks
of each type. Thus, the wrong type is sometimes misapplied to an application, resulting in
inferior performance.
This article will present an engineering based comparison of the two predominant linear
motor types, with the objective of providing the reader with the knowledge needed to
properly specify the correct type of motor for a given application. Real world examples
of both motor types will be presented.
Specific topics will be discussed, including:
• Thermal considerations
• Stiffness, dynamic and static
• Efficiency
• Real definition of important, but often misused parameters like cogging, force ripple,
commutation ripple, and other terminology, and their effect on motor performance
versus the type of motor
• Force density
• Accuracy, velocity, stability, settling time
• Use of Hall effect sensors for initialization and current commutation; effect on
performances
• Influence of the servo controller
• Magnetic attraction
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1
Ironless versus ironcore motor solutions
HST-Etel Inc. 09/17/03
The different linear motor types
As a first step, a linear motor can be considered as the unrolled version of a brushless DC rotary motor. The
rotor with permanent magnets would changed into a flat linear magnetic way, also called secondary, which
is generally used as the fixed part of the motor. The stator is changed into a flat linear coiled part, also
called forcer, glider or primary, which is generally used as the moving part.
The design of the magnetic ways and the material that the forcer is composed of will determine the nature
of the linear motor, ironless or ironcore.
Ironless motor
As its name implies, an ironless linear motor, also called
air-core motor has no iron inside. The glider is basically
a plate made of epoxy where the copper coils are
inserted. The forcer slides in between two rows of
magnets that are facing each other. They are linked on
one side by a spacer. This is also called a U-channel
magnetic way. By design ironless motors peak power
range is limited to a few thousand Newtons. The peak to
continuous force ratio is generally high (typical factor of 4 or more) and these motors are typically used in a
high dynamic demanding application where payload is light. In application where very high smoothness of
motion is required, ironless motors are preferred due to the absence of detent force.
Ironcore motor
The ironcore motor is composed of a slotted lamination
stack made of steel. Laminations are insulated from each
other in the same way as they are in a rotary motor, which
reduces Eddy currents that would result in too high iron
losses. By design ironcore motors peak force range can go
up to several tens of thousands of Newton. By design there
is a wide range of sizes available for the ironcore linear
motors. The motor choice will be based upon the overall
dimensions affordable in the application. The peak to
continuous force ratio is usually in the range of 2.5 for a motor used with forced air cooling. Motor width is
typically from 30 to 300 mm whereas length can vary from 50 mm up to 800 mm or more.
High duty cycles and low heat dissipation
From automation to semiconductor and electronics industries, the constantly increasing requirements for
throughput improvement, flexibility and dynamics in the machines has led the manufacturers to opt for the
“direct drive” approach.
As with any other kind of motor, heat is generated during operation. Since the motor is directly linked to
the payload in the middle of the mechanics, this heat has to be efficiently removed to avoid any thermal
drift in the machine.
If ones wants to evaluate the thermal behavior of a given motor, a key parameter has to be looked at, the
motor constant or Km. This parameter is defined as the ratio between the force that a motor is capable of
producing and the square-root of its power dissipation at this force level. Typical S.I. units of Km are
N/√W. In other terms, this is a picture of the efficiency of the motor. The higher the motor constant, the
more efficient the motor would be. When comparing different motors, ones should make sure of comparing
the different Km calculated at identical conditions. The motor constant is proportional to mainly these
factors.
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Ironless versus ironcore motor solutions
HST-Etel Inc. 09/17/03
K m ≈ l a Bδ .
S enc .K cu
lm
where :
la
Bδ
Senc
Kcu
lm
Motor width
represents the magnet field
represents the section of the slot
represents the copper filling factor
is average length of one turn of the coil
The rare earth materials that the magnets are made of will fix the magnetic field level. The most commonly
chosen compromise between power capabilities and price is for the Neodymium-Iron-Bore material.
Open slots design
The magnetic design of the motor will determine the section of the
slot (Senc), whereas the last two parameters (Kcu, lm)are more linked
to both magnetic design and coil manufacturing process.
Etel has patented an opened slot design that allows to manufacture
the coils as a separate part of the motor in a very compact and dense
way. It is then possible to get a very high copper filling factor (up to
60% ) and thus a very high km depending on the motor size.
One of the most important considerations to use a linear motor in
machine design is heat dissipation. Here is where there are
significant differences between ironcore and ironless motors. The
heat generated by the motor can be dissipated thanks to the inherent conduction, convection and radiation
properties. The design of each motor intrinsically characterizes the most efficient method of heat transfer.
•
In the thermal conduction process, the heat transfer is directly dependent on the surface of
attachment of the motor to the mechanics and on the thermal conductivity of the structural
material of the motor. Typical thermal conductivity of epoxy is 1.02 W/(m.K) whereas iron’s is
50 W/(m.K).
In the ironcore motor, the lamination stack acts as a natural heat sink, whereas the epoxy structure
of the ironless motor acts as a barrier to heat transfer. This conduction ends up as convection in
free or forced air.
Thermal conductivity
Young Modulus
W/(m.K)
GPa
Aluminium
204
70
Steel
50
210
Copper
384
130
Epoxy
1.02
•
Convection represents 1/3 of the total heat transfer in a free mode. The impact of convection on
motor cooling can be important especially in applications where the movement amplitudes are
large and the speed is high.
•
Radiation contributes in major way to the heating up of the magnets whose power is strongly
dependent on their temperature, and then to the heating up of the structure. Radiation contributes
in a 2/3 ratio to the total heat transfer. The higher the temperature, the lower the magnets power. In
an ironless based system, the motor is radiating on both sides to the two rows of magnets, which
can lead to a fast increase of their temperature. In an ironcore solution, the motor radiates on one
row of magnets only.
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3
Ironless versus ironcore motor solutions
HST-Etel Inc. 09/17/03
Force density
The first parameter that
Comparable continuous force (coils@80°C) are assumed for the motors
will certainly help make
Areas calculated correspond to the active surfaces of the motors
a decision whether to go
with ironless or ironcore
is the force density
available with each of
them. In the attached
graph, you can see that
for a given level of
continuous force, the
ratio force per active
Ironcore Motors
surface unit can be up to
Ironless Motors
2 times greater for the
ironcore
motor
technology than for an
Continuous force (coils@80°C) with free air cooling
ironless one. In other
terms, this means that for a given level of continuous force, an ironcore motor can be up to 2 times smaller
than an ironless one. This can be a key parameter in applications where compactness is needed.
0
0
50
100
150
200
LMA11-100
ILM12-060
ILM06-060
ILM06-040
0.2
ILF12-030
0.4
LMA11-070
LMD06-050
0.6
ILM12-040
0.8
LMA11-050
1
LMD06-030
LMD03-030
LMD05-030
1.2
ILF03-030
ILF06-030
ILF09-030
Force density (N/cm2)
1.4
LMD10-050
1.6
250
300
350
400
450
How to make your machine even cooler!
One can bet you want your machine to be very cool! Let’s see how motors options can help make it even
cooler. Since the linear motor is generally buried into the mechanics, it has to be kept as cool a possible to
avoid too much power dissipation and then mechanical distortion.
By design, ironcore motors are easy to equip with a cooling option. To help remove the heat dissipated by
the motor, different coolants can be envisaged.
The water cooling of ironcore motors is the preferred solution in heavy duty applications where
payloads are high. This is typically the case in machine tool applications. A water cooling allows
continuous ratings that are 200 to 300% greater compared to non water-cooled motors.
Until recently, air cooling of linear moors was not very effective, since most manufacturers simply
blew forced air into the cooling channels instead of water. Etel’s innovation was to design a motor
specifically (and exclusively) for air cooling. This method has lately proven to also be very efficient
when blown at the right location in the motor. This technique allows to increase the continuous ratings
of the motors by almost 20% compared to the non-cooled version. This is an unprecedented
improvement in the effectiveness of air cooling.
Ironless motors due to their inherent low efficiency can benefit more from air-cooling. Some manufacturers
claim more than 50% increase of the continuous ratings.
An alternative to cooling down the motor is to let it heat up. In that case, the motor has to be well insulated
from the mechanics. This solution leads to a decrease of the motor performances since the continuous
ratings are generally described based upon a given amount of heat dissipation through the mechanics.
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Ironless versus ironcore motor solutions
HST-Etel Inc. 09/17/03
Heavy-duty application with ironcore motors: a PCB drilling machine
(Courtesy of Posalux)
This PCB drilling machine is integrating mainly two kinds of tools
namely drilling and milling cutters.
• The Y axis is moving a table holding several PCB ready to be
drilled. The Y motor is doing a back and forth movement as
shown on the attached picture. The moving mass is of about 500
kg. Acceleration in the range of 1 g and the speed of about 1
m/s.
• The X axis is doing a movement from left to right on the
attached picture and supports up to 10 different working
stations. The moving mass on the X axis is in the range of 350
kg depending on the configuration. Acceleration and speed are
in the same range as for the Y axis.
• Each working station is equipped with a Z axis moving from top
to bottom on the attached picture. The moving mass is in the
range of 8 kg and the acceleration can be up to 4 g’s.
Z
X
Y
High smoothness of motion and non mechanical bearing
applications
Apart from the thrust force itself, additional forces can be generated in a linear motor depending on its type.
In applications where a perfect smoothness of motion is required, the system generally integrates air
bearings. Perturbating forces are thus not desirable. They can be easily overcome by an appropriate
magnetic design or servo controller choice.
Force ripple is the result of two effects namely the cogging (or detent force) and the commutation effects.
The cogging is always present in an ironcore motor. Indeed, the force between magnets and lamination
stack causes not only an attraction force but a force in the direction of motion as well. This force depends
on the relative position of the laminated teeth with regards to the magnetic poles. The cogging is
independent of the current flowing in the motor. Nevertheless using techniques like skewing lamination
stack or magnets can drastically reduce this effect. Choosing an appropriate and optimized combination of
teeth and magnetic pitches will provide the same effect as skewing one or the other part.
The choice of the right angle of clearance at the both ends of the linear motors will help reduce the cogging
induced by the end effect.
Ironless motors do have zero cogging since the moving part has no iron at all. Ironless motors will therefore
be the right solution when an extremely high smoothness of motion is required.
The commutation effect can be generated by both motor and electronics. The motor can generate force
oscillations if the back emf voltage is not a perfect sinus. Electronics will induce force oscillations as well
due to current ripple.
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Ironless versus ironcore motor solutions
HST-Etel Inc. 09/17/03
Reducing the ripple force is possible. As a stage mapping can help improve the accuracy of a mechanical
slide by learning the mechanical defaults and compensating for them, a ripple compensation can be
envisaged in the electronics to reduce force ripple. In that case, the actual force ripple will be measured at
different positions and stored in a table. The current loop will then integrate a corrective current value
associated with a given position of the motor along the magnetic period to balance the ripple force.
A typical electronic compensation can easily reduce the force ripple by a factor of 5 and even up to a factor
greater than 10.
If iron is needed to concentrate the magnetic flux in an ironcore motor, one of the major penalty of having
iron in front of magnets is that a very high attraction force is generated. Depending on the motor size, this
attraction force can be up to 6 times greater than the motor peak force ratings.
Depending on the type of guiding system that is used, mechanical, aerostatic or hydrostatic, this attraction
force can be a good help or a bad problem to overcome.
All the mechanical ball bearings available on the market today have huge load capacities which will
overcome the attraction force level without any problem. It is then a matter of choosing the right size of
rails depending on the harshness of the application to ensure a reasonable lifetime.
As opposed to mechanical bearings which stiffness is very high, air bearings have no or very low stiffness.
In order to generate the film of air that is required between both moving and static parts, a preload is
required. The attraction force of the ironcore motor can be used as an efficient way of preloading the
bearing. Etel is typically providing ironcore motors to manufacturers of grinders for machines using
hydrostatic bearings.
The main problem is that the attraction force is not of constant intensity depending on the current that flows
in the motor. If the attraction force is defined at zero current, its value at peak current can vary within
±10%. This particular point makes the choice of an ironcore motor for a system based on non-mechanical
bearings difficult for application where very high smoothness of motion is required. For these applications,
an ironless solution would be preferred because of the absence of attraction force and related fluctuation.
A semiconductor application: Die bonding machine (courtesy of Muhlbauer)
Optimized for high speed eutectic and epoxy processes, this die bonder is designed to
deliver high throughput, high reliability and very high yield.
The machine is composed basically of an X and a Z axes. Four linear ironless motors
are used to perform the very stringent specifications characterizing the
machine. The peak force is 400 N per axis whereas peak
acceleration is in the range of 15 g’s and maximum speed is
up to 4 m/s.
Coupled to very high performances drives, this machine is
the fastest one on the semiconductor market with its 0.2
second cycle time per component (5 components per
second). The maximum authorized overshoot is 3 microns.
To respect the die’s positioning accuracy on the lead frame,
the repeatability of the movement must be within less than
1 micron. When the movement starts, the final position is
not yet known. A correction is performed “on the fly” in
real time thanks to a vision feedback to the position
controller and thanks to a very high communication rate
between the PC and the servo controller during the whole
Ironless motors fits perfectly this application where
compactness and very high dynamics are required and light moving mass is involved.
trajectory.
Clean room, vacuum and magnetic field sensitive applications
Often referred as to non contact motors, linear motors are therefore perfectly suited to work in a clean
room environment. On standard both ironless and ironcore motors can work in an ISO6 class (former Class
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Ironless versus ironcore motor solutions
HST-Etel Inc. 09/17/03
1000). An ISO class5 (Class 100) or below will require special cares with regards to the materials that are
used such as cables, magnets coating etc…
Vacuum applications in the range of 10-3 mbars (750 Torr) do not require any special care with regards to
the materials that the motor is composed of. When this vacuum level drop to a lower value, cables, magnet
coating, and epoxy resins have to be chosen as non-outgasing materials.
8
4
Magnetic field sensitivity is often an issue in some applications
where electron beams are used. This is typically the case in e-beam
metrology tools, SEM (Scanning Electron Microscope) or ion
implanters devices.
The magnetic field
Y=95
around the motor has
100
to remain as small as
70
possible in order not
to make the e-beam
deviate
from
its
trajectory.
By
Plate
Magnet
construction, the U
shape of the ironless motor magnetic ways make the magnetic
field self contained in the magnetic way. As shown on figure
X, the magnetic field measured around a magnetic way of ironless motor is of a very small amplitude as
opposed to the measurements taken on an ironcore motor magnetic way that constitutes an open structure.
Position and speed stability applications
Increasing the stiffness
Short settling times associated with high dynamics or high position stability requires stiff mechanics.
Stiffness related to both type of ironless and ironcore motors is composed of three components: the motor
built-in stiffness, the motor mounting stiffness and the servo-loop stiffness.
Motor built-in stiffness - The epoxy structure of an
ironless motor has a low inherent stiffness. The motor
rigidity is given by the copper coils that are inserted and
is dependent on how the coils are physically put together:
separated or overlapped. An overlapping configuration
would lead to a higher bending stiffness compared to a
construction with independent coils whereas the lateral
stiffness will be almost identical in both overlapping and
separated configuration.
The steel structure of an ironcore motor make it obviously
much stiffer than an ironless solution.
Figure : Mounting of an ironless motor
Small contact area, cantilevered support
Mounting stiffness - By design, the mounting surface of an ironless motor corresponds generally from
10% to 25% of the active surface of the motor. The attachment surface is located on one side of the motor.
Besides allowing almost no thermal conduction, this kind of mounting can be problematic when high
position stability or very tight settling times are
required. The main reason is that the current that is
flowing in the motor phases can excite the transversal
natural frequency of the motor, leading to oscillations
once in position.
In an ironcore motor, the mounting surface is generally
100% of the active surface of the motor and centered
above the motor. The stiffness of this mounting is
Figure : Mounting of an ironlcore motor
Large contact area, uniform over motor
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7
Ironless versus ironcore motor solutions
HST-Etel Inc. 09/17/03
therefore much higher. As long as the carriage is stiff enough to withstand the attraction forces, no
vibration problem should be foreseen.
Servo-stiffness - Ironcore or ironless, a linear motor provides a zero stiffness in the direction of the
movement when the power is off. Once the power is on, the stiffness is given mainly by three factors:
• The stiffness of the mechanics
• The encoder resolution
• The servo amplifier sampling rates on both current and position loops
Figure x shows a typical graph of the stiffness of a linear stage versus the perturbating frequency. This test
has been performed with an Etel’s linear ironcore motor moving 250 kg and an Etel’s amplifier.
One can see on this graph that the servo-stiffness is decreasing with the increase of the frequency up to a
frequency corresponding to the natural frequency of the load. The stiffness then increases again. The
stiffness never recede 400N/µm.
Stiffness in N/um
10000
Natural frequency given by
a 250 kg moving mass.
(Calculated)
1000
Measured stiffness of
the system in closed
loop
100
1
10
100
Frequency in Hz
1000
Figure x: Servo Stiffness with a linear motor moving a mass of 250 kg
Influence of servo controller
Whether an ironcore or an ironless solution is integrated in a given application, the final specifications are
directly linked to the servo controller characteristics. Special care should be taken to choose a digital servo
controller as well as a digital servo amplifier with encoder commutation. High position and current loop
sampling times and a high interpolation factor on the feedback signals will allow to get the required servo
stiffness and final resolution on the stage.
•
Printing application with an ironcore motor (ARRI)
To create special effect on movies, each image has to be digitalized to be modified on computers. After
adding the special effects, the image has to be re-printed on the tape, This can be done by using special
scanners and lasers. This last operation usually takes 25 seconds. Etel has developed a linear stage
equipped with an ironcore motor capable of decreasing this time from 25 to 5 seconds. With 24 images
per seconds, the time saving is dramatic.
To avoid any deformation on the screen, no default are allowed on the image itself on the tape. Thus the
speed stability during the scanning movement is crucial.
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8
Ironless versus ironcore motor solutions
HST-Etel Inc. 09/17/03
The laser beam and the stage are controlled
and synchronized with an Etel’s electronics.
The linear stage has a stroke of 29 mm and is
moving at 6mm/s at a speed stability of 0.2%
all along the stroke (measurement frequency is
1 kHz).
These performances are achieved thanks to
ETEL’s state of the art DSB2 drive electronic,
a linear encoder from Heidenhain and special
linear bearings in order to minimize any
mechanical perturbation. ETEL’s ironcore
linear motor is implemented in this stage.
With this stage, the measured tracking error is
70 nanometer and the position stability has
been measured at 3 nanometers.
Courtesy of Arri
Tracking at constant low speed
Start position : 16.5 mm
150.00
Tracking error (M2)
Positive tolerance
100.00
Negative tolerance
50.00
0.00
- 50.00
-100.00
Standard deviation at 6 m m /s : 6.44
Tracking error w ithout filter : -2.81
-150.00
0
100
200
300
400
500
600
700
800
900
1000
Ti me i n ms
The costs of linear motor solutions
There is often a misconception about the cost of a linear motor solution. How compare prices of the two
solutions? To be compared to alternative solutions like brushless servo motor and ballscrew or belt, ones
will take care of taking all the relevant costs into account. A linear motor is a contact-free motor which
means that the maintenance costs associated are drastically reduced. The number of parts in the mechanical
assembly will be reduced as well.
The ironless solution is almost never cheaper than an ironcore solution. The main reason for that is that the
cost of a linear motor is primarily related to the price of the magnets. For a given level of force required,
when an ironless magnetic way requires two rows of magnets, an ironcore motor requires only one. The
longer the stroke in the application the more obvious the price difference is. Hereby is a graph that shows
typical price difference between an ironcore and an ironless motor solutions for a defined application.
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9
Ironless versus ironcore motor solutions
HST-Etel Inc. 09/17/03
0
0
500
ILM12-060
LMA33-070
ILM09-060
LMA33-050
ILM12-040
LMA22-070
ILM09-040
ILF15-050
LMA22-030
0.1
LMD10-050
LMD03-030
LMD06-030
0.2
LMA11-030
0.3
LMA22-050
ILF12-050
LMD10-050
0.4
ILF15-030
0.5
ILF12-030
0.6
ILF06-030
0.7
ILF03-030
Relative Price (USD)
0.8
LMA11-070
0.9
IILM06-040
Comparable peak forces are assumed for the motors
Usable stroke of 300 mm
1
Ironcore Solution
Ironless Solution
1000
1500
2000
2500
3000
Peak force level (N)
Figure: Relative price comparison for Ironless and Ironcore solution for a given application
The power-on issue
Initialization and current commutation
As any synchronous motor, the current injected in the motor has to be synchronized with the back emf
voltage generated by the motor. This is done through the initialization process that takes place at the switch
on of the amplifier. Three main methods are commonly used to perform this synchronization, depending on
the motor type as well as on the electronics capabilities.
• Initialization by constant current
A constant current is generated in one motor phase. The motor moves to a stable position where current and
back emf are 90° shifted.
• Initialization with Hall effect sensors
Hall effect signals sent to the servo-amplifier input allow it to estimate the commutation phase within ±30°
upon power up. The phase resolution is good enough to drive the motor. Once a transition point of any of
the Hall effects is passed, the servo-amplifier detects it and adjust the phase position accordingly.
• Initialization by pulse
This type of initialization is not common but available with more sophisticated digital amplifiers. It allows
a very accurate initialization without any movement of the motor. This is typically required to prevent
tooling or part damages after a power failure on the main supply. At the next power on, without any
movement on the motor, the amplifier has to be able to properly commutate the current.
Linear motors can be commuted trapezoidally using Hall effect sensors or sinusoidally using linear
encoders in conjunction with the appropriate motion controller or sinusoidal amplifier. Obviously a
sinusoidal commutation allows very high interpolation factor that will let reach high resolution on the
amplifier and then on the final stage.
Why always move the motor?
In applications where small strokes are needed, it is very useful to keep the motor static and have the
magnetic way moving. This rids the designer of the cable management problem and helps reduce the
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Ironless versus ironcore motor solutions
HST-Etel Inc. 09/17/03
moving mass. The reasonable stroke limits for such a solution should not exceed 100-150 mm. This
particular application case cannot be easily envisaged with the use of an ironless motor due to the U shape
of the magnetic way and its associated weight. Ironcore motors would be preferred in that case.
6 myths about linear motors
1.
Linear motors are too expensive
2.
Ironcore motors can’t be used
in ultra-precision applications
3.
Linear motors get too hot to be
used
in
high-precision
application
4.
A linear motor has to “jump” to
initialize (uncontrolled initial
movement)
High dynamic can not be
achieved with ironcore motors
5.
6.
Air bearings require ironless
motors
Wrong. Direct driven solution can compete with non direct driven
ones thanks to benefits such as the following ones:
• reduction of maintenance costs
• increase of the machine throughput
• smaller number of mechanical parts
• simplicity of integration
• lower cost: ironcore motors can be used in many applications
that previously required ironless motors
Wrong. Ironcore motors applications can provide results like:
• Nanometer position stability (semiconductor applications)
• Tracking error at low speed in the sub-micron level (printing
applications)
• Very high Smoothness of motion (scanning applications)
Wrong. As any motor, linear motors heat up during operation but
different solutions are available to limit or remove the heat
generated or to stop it from going into the mechanics:
• Ironcore motors are very efficient (low level of losses for a
given level of force)
• Insulation of the motor
• Air or water cooling available
Wrong. Linear motors can initialize witthout any movement
thanks to Hall effect sensors. Better, ironcore motors can initialize
without movement and without Hall effect sensors
Wrong. There is no physical reason why an ironcore motor would
achieve lower dynamic than an ironless motor. Thanks to a very
good mechanics and an appropriate servo-controller, ironcore
motors can achieve 25 g’s and more.
Wrong. Ironcore motors can be used with air bearings as well. The
attraction force is then used as a preload. It depends on the
complete application to determine the best approach.
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Ironless versus ironcore motor solutions
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Which motor to choose?
Application requiring or implying:
•
•
Sensitivity to magnetic field
Continuous force > 500 N
•
Peak force > 2,500N
•
Air bearings with perfect smoothness of
motion
Air bearings with relative smoothness of
motion
Hydrostatic bearings with perfect
smoothness of motion
Hydrostatic bearings with relative
smoothness of motion
Down to nanometer position stability
Speed stability
•
•
•
•
•
Should integrate
Ironless motor
Ironcore motor
Recommended
Possible
with
several
motors
electrically mounted in parallel
Possible
with
several
motors
electrically mounted in parallel
Recommended
Not Recommended
Recommended
Possible
Possible
Recommended
Not recommended
Possible
Possible
equivalent
Equivalent (up to 0.1% at 1 Khz)
Recommended
Impossible
Possible
Not recommended
Possible
Recommended
Recommended
Possible
•
•
•
Several motors on the same axis
Thermal dissipation kept at the lowest
level
Tight dimensional constraint in the
overall length
Tight dimensional constraint in the
overall height
Very high acceleration (>10 g’s)
Very high speed (>10 m/s)
Stroke <150 mm
Equivalent (but cheaper)
Recommended (up to
0.1% at 1 Khz)
Recommended
Highly recommended
Possible
Possible
Possible
•
•
•
•
•
•
•
Vertical axis
Very long stroke (>1000 mm)
Lowest possible price
Vaccum application
Clean room application
No move for initialization at power on
Safety margin on continuous force
Possible
Possible
Not recommended
recommended
Possible
Possible
Possible
Possible
Possible
Recommended
magnet)
Possible
Recommended
Recommended
possible
Possible
Recommended
Recommended
•
•
•
•
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Ironless versus ironcore motor solutions
HST-Etel Inc. 09/17/03
(moving