Servo Motor - Linear Shaft Motor FAQs

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Not difficult, just a little different. The Linear Shaft Motor is simpler to install, as it replaces the ball screw, nut,
end bearings, motor mount, couplings, and rotary motor. Alignment of the Linear Shaft Motor is not critical (even
for high performance packages) and consists of mainly ensuring there is some clearance between the forcer
and shaft over the entire travel. Nippon Pulse will assist with selection of suitable components.

Yes, the Linear Shaft Motor can be built for a variety of operating environments. To determine if and which
Linear Shaft Motor is suitable for a specific application, an applications engineer must review the specifications.

Yes, a linear motor provides the same performance when mounted vertically or horizontally. However, it is
recommended that a vertically mounted Linear Shaft Motor be counterbalanced.

Yes, more than one forcer can be used in conjunction with a single shaft as long as the forcers do not
physically interfere with each other. Two forcers may also be tied together and driven with one drive to double
the output force.

Yes, it is possible. To determine which Linear Shaft Motor is most suitable for your specific application, an
applications engineer must review the specifications.

The Linear Shaft motors use a rare earth magnet, which will maintain their strength for 99 years. However,
when operating at high temperatures (>150°C), these rare earth magnets can lose strength. Lower
temperatures have no effect the magnets as long as frost does not form in the air gap.

The Linear Shaft Motor is designed to operate with most off-the-shelf motor controls and drives.Basically, the
Linear Shaft Motor uses the same electric circuit as other linear motors and rotary servo motors.

In an application where two coils are connected to the same drive, the same coil of each drive must be
above the same magnet in order to run. (See drawing below) This is why when the second forcer is flipped the
U and V leads must also be flipped. As such only one of the two coils needs to have halls.

By eliminating the conversion of rotary to linear motion, a major source of positioning error is removed. This
results in high performance and accuracy. While the Linear Shaft Motor itself does not have inherent resolution,
position accuracy is ultimately determined by the linear encoder feedback accuracy and the core stuffiness of
the Linear Shaft motor. Testing has shown that with encoder resolutions less then 10nm, the Linear Shaft Motor
will, at worst case, enable a position accuracy of ±1.2 pulses of encoder resolution. This position accuracy is not
affected by the expansion and contraction of the shaft.

While the Linear Shaft Motor itself does not have inherent speed limitations. There are several factors that
can limit the maximum speed of a Linear Shaft Motor system. The control must provide sufficient bus voltage to
support the speed requirements. The encoder itself must be able to respond to that speed and its output
frequency must be within the controllers capability: for example, with a 0.5 micron encoder and a speed of 5
m/s, the controller must handle 10MHz. Finally the speed rating of the stage’s bearing system must not be
exceeded: for example, in a recalculating ball bearing, the balls start to skid (rather than roll) at about 5 m/s.
Under the right conditions the Linear Shaft Motor can reach speeds exceeding 10 m/s.

The advantages of the Linear Shaft Motor include higher velocities [>240 in/sec (>6 m/s)], non-wear moving
part, free movement when power is off, no backlash because there are no mechanical linkages, easer
alignments, and easier manufacturing.

If a power loss occurs, the system loses all stiffness. So, if the payload is moving, it will continue to move until
it hits a stop or until friction brings it to a stop. If the system is already stopped, it will not be affected. If the
feedback loop is lost, it may lead to a runaway situation. This condition can be avoided with the use of soft and
hard stops as well as braking systems.

RMS is the average current flowing through the windings. RMS current for a given application should not
exceed the rated continuous current for the selected Linear Shaft Motor.

Linear Shaft Motors are direct drive linear servomotors that consist of a shaft with permanent magnets and a
forcer of cylindrically wound coils.

Cogging is the tendency of some linear motors to move in discrete distances rather than infinitely variable
distances. The effect is a result of varying magnetic forces along the length of motor travel. This effect is most
often seen when ferrous material is used in the motor or stage construction.

Duty cycle for a linear motor is different then other types of systems. While it is defined as (time on) / (time on
+ time off) per cycle, in a linear motor the motor can be on even when not in motion. So for a linear motor the
duty cycle is based upon the time the motor is actually working (when current is applied) and NOT the % of time
the motor is moving! Thus it is best defined as:
Motion duty cycle is defined as time moving / total time. It is possible for Motor power duty to be 100% while the
motor is not moving, or the motion duty to 100% with very low motor power duty.

The rated current is what the motor is rated at. The peak current refers to the amount of current the driver outputs.

Non-microstepping drivers
Peak Current = Rated Current

When using a driver that only does full stepping, the rated current is the same as the peak current. (Rated current = Peak Current).

Microstepping Drivers
Peak Current = 1.4 x Rated Current

When using a driver that is capable of doing microstepping (microstepping = 1/2, 1/4 stepping or more), the definition of peak current becomes 1.4 times the rated current. Microstepping drivers are made differently in order to maximize their ability to drive the stepper motor. Therefore, step motors can handle up to their rated current multiplied by 1.4. (Peak Current = 1.4 x Rated Current). This will not damage the motor because the power output is more or less the same.

To determine a motor’s resonance, take the square root of (torque stiffness divided by total inertia). Although resonance frequency cannot be completed eliminated, it can be changed by altering the rotor or system inertia or by altering the torque stiffness.

The current published MTBF for the Linear Shaft motor is over 100,000 hours of operation.

The price of the Linear Shaft Motor is comparable to other ironless core linear motors. Prices for other parts
of the system are dependent upon the resolution and size of the system being produced.

The Linear Shaft Motor is a non-contact device. As such, it does not have any parts that can wear out. If the
system is designed properly, and the operating parameter limits are not exceeded, a Linear Shaft Motor should
last indefinitely.

 In most applications, repeatability and accuracy will be increased. Move times and settling time will be
decreased. Noise will also decrease as well as total power requirements.

The Linear Shaft Motor itself is entirely maintenance free. It does not have any parts that can wear out. NPA
does recommend that you perform periodic minimal inspections. Please see the Maintenance and Service
section of the Installation and Users Guide for a full list.

The smallest Linear Shaft Motor will produce 0.29N [0.07 lbs] of continuous force. The largest can provide
36,000N [8180 lbs] of peak force.