Linear Servo Motor FAQs

Are versions of the Linear Shaft Motor available for use in waterproof, vacuum or clean rooms?

Yes, the Linear Shaft Motor can be built for a variety of operating environments. To determine which Linear Shaft Motor is suitable for your application, contact an applications engineer to review your specifications.

Can a Linear Shaft Motor be mounted vertically?

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 to reduce RMS and counteract the impact of gravity on the motion system.

Can more than one forcer be used with a single shaft?

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.

Do magnets ever lose their magnetism over time?

The Linear Shaft Motors use rare-earth magnets, which are the strongest magnets available and produce magnetic fields that are significantly stronger than any other type of magnets. However, when operating at high ambient temperatures (>80°C), these magnets can lose strength. Lower temperatures have no effect on the magnets.

Do standard rotary motor electronics work with linear motors?

Yes they do. In most cases, the only differences between the two is the terms used in the software and manuals. For example, torque will become force; RPM will become velocity. A Nippon Pulse applications engineer would be happy to assist you in understanding the corresponding terms in your case.

How accurate are Linear Shaft Motors?

The Linear Shaft Motor is a high-performance, accurate motor. There is no need to convert rotary motion to linear motion, which is a major source of positioning error among rotary-to-linear systems. While the Linear Shaft Motor does not have inherent resolution, position accuracy is ultimately determined by the linear encoder feedback accuracy and the core stiffness of the motor. Testing has shown that, with encoder resolutions less then 10nm, the Linear Shaft Motor will, at worst, 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.

How can an encoder be used to determine position and speed?

There are many different types of encoders. The basic function of an incremental encoder is to output signals that help the control electronics determine the speed and direction of travel of the motor. The control electronics then use calculations to determine the relative position of the motor. The basic function of an absolute encoder is to output signals that help the control electronics determine the exact position of the motor. The control electronics then use calculations to determine the relative speed and direction of travel of the motor.

How fast can the Linear Shaft Motor go?

The maximum speed is a two-step calculation. First, max acceleration is calculated by (acceleration = accl force / mass). Second, the maximum speed is calculated by (velocity = acceleration * time). Outside of this, 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 must be able to respond to that speed, and its output frequency must be within the controller's capability. Finally, the speed rating of the stage's bearing system must not be exceeded.

In a tandem or parallel drive-application, do both motors need Halls?

In the case where both forcers are connected to the same drive, no; only one motor needs Hall effects. In an application where two forcers are connected to the same drive, the same phase of each forcer must be above a like magnetic pole in order to run. As such, only one set of Halls is needed by the servo drive.

In the case of each forcer being connected to separate servo drives that require Halls, yes; you will need Halls on both motors.

In certain tandem forcer applications, why does one motor need to be physically flipped?

The physical flipping of one of the two forcers in a tandem configuration is sometimes used to reduce the overall footprint while maintaining the magnetic alignment of the two forcers.

Is the Linear Shaft Motor difficult to integrate into a machine?

One of the key design aspirations of the Linear Shaft Motor is simplicity. That simplicity extends to the integration process. As all systems are different, it is generally difficult to make specific statements about machine integration that hold true. A Nippon Pulse applications engineer would be happy to assist you with integration questions relevant to your individual project.

Should I worry about heat dissipation?

If your motor will operate in a confined space, or if you plan to run your motor beyond its rated capabilities, you should be concerned about heat dissipation in your application. If your motor is in a confined space, you should consider how the heat given off from the motor might affect nearby components and raise the ambient temperature. If you plan to run the motor above its rated specs, you should consider ways to cool the motor proportionally to keep it operating near its specified maximum temperature.

What advantages does the Linear Shaft Motor offer over traditional linear motion systems?

The Linear Shaft Motor is the first linear servomotor designed for a the ultra high-precision market and, as a result, has several advantages over traditional linear systems. The Linear Shaft Motor is compact and lightweight, has no cogging issues, is up to 50 percent more energy-efficient than traditional linear motors, and features a non-critical air gap, which reduces maching costs.

What are the advantages of the Linear Shaft Motor over a lead screw?

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, easier alignments, and easier manufacturing.

What happens if the system loses power or velocity feedback?

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 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.

What is a 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.

What is cogging?

Cogging is a resistive torque or force caused by the interaction of a magnetic field with a ferrous (magnetic, iron-containing) material, even when there is no current present. Cogging causes jerky, uneven motion in servo systems.

Because our Linear Shaft Motor contains no ferrous material, it does not experience cogging effects.

What is continuous current? What is peak current?

Continuous current is the current that can be supplied from the driver indefinitely. The peak current refers to the maximum 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 taking microsteps (at a rate of a half-step, fourth-step or any other fraction of a step), 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.

What is motor motion duty cycle for a motor?

Motion duty cycle is defined as (time moving/total time). It is possible for motor power duty to be 100 percent while the motor is not moving, or the motor's motion duty to be nearly 100 percent with very low motor power duty.

What is motor power duty cycle for a motor?

Duty cycle for a linear motor is different than for other types of systems. While it is defined as (time on) / (time on + time off) per cycle, in servo systems the motor can be on even when not in motion. Thus, for a servo motor, the duty cycle is based upon the time the motor is actually working (when current is applied) and NOT the percentage of time the motor is moving. It is possible for motor power duty to be 100 percent while the motor is not moving, or for the motor's motion duty to be nearly 100 percent with very low motor power duty.

What is RMS Current?

RMS stands for "Root Mean Square." It is the effective average current. It is most commonly used when referring to AC current.

What is system resonance?

To determine system 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.

 

What is the MTBF (Mean Time Between Failure) for the Linear Shaft Motor?

The Linear Shaft Motor components operate in a passive manner when properly designed into your system. As such, there is no MTBF on the motor.

Any installation that causes any component of the motor to be active (example: flexing of supplied lead wires, using shaft or forcer as load-bearing member, etc.) is beyond the intended design of the Linear Shaft Motor. This will void the warranty and is done at your own risk.

With the proper settings, the Linear Shaft Motor will not wear out.

What is the reliability of the Linear Shaft Motor?

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, the Linear Shaft Motor should last indefinitely.

What routine maintenance is required for Linear Shaft Motors?

The Linear Shaft Motor itself is entirely maintenance-free. Because of its simple structure, the Linear Shaft Motor does not have any parts that can wear out. However, Nippon Pulse recommends you perform periodic inspections on all systems, including the bearings and supports. See the Maintenance and Service section of the Installation and User's Guide for details about the recommended inspections.