Linear Motor FAQ's

Moog's engineering experts have compiled the following list of your most popular linear motor questions. The topics covered include everything from general concepts to friction, detent force, physical tolerances, shaft bearings, performance and encoders. Please contact us if you have a question that is not addressed below.

 

General

Q: WHY MOOG LINEAR MOTORS?
Moog linear motors offer many advantages over pneumatic, hydraulic and electromechanical systems, including the ability to:

  • stand alone without the need for pneumatic or hydraulic pumps and infrastructure
  • reduce deployment and maintenance costs
  • have a single moving part, the shaft, which with proper maintenance can greatly extend the period between service intervals
  • offer high force, shaft speeds and acceleration
  • have precision position accuracy and stiffness with no backlash
  • require only 5 ml of oil added every 6 months for routine maintenance

 

Q: WHAT ARE THE APPLICATIONS OF MOOG LINEAR MOTORS?
Moog linear motors are deployed wherever direct linear motion control is required, replacing pneumatics, hydraulics, electromechanical, as well as rotary to linear mechanisms. Applications have included:

  • food processing
  • testing / inspection machines
  • sorting
  • packaging
  • industrial
  • wood / paper processing

 

Q: DOES MOOG OFFER COMPLETE SYSTEM SOLUTIONS?
Yes, Moog can provide a complete linear motion control solution that includes motors, drives, multi-axis controllers and accessories (such as cables, filters, brake resistors and encoders).

complete system solutions

 

Q: WHAT IS THE DIFFERENCE BETWEEN STANDARD AND HIGH RESPONSE WINDINGS IN THE LINEAR MOTOR?
A standard response winding is used in systems with large mass. A high response winding offers higher speed and acceleration and is used for high precision and / or highly dynamic motion.

The difference in performance of the standard “C” winding and high response “D” windings are further defined and illustrated in data sheet “High Performance Linear Servomotor” (MS3018) and “Linear Motors Product Overview” (MS3130).

 

Q: HOW ARE MOOG LINEAR MOTORS THERMALLY PROTECTED?
Standard Moog linear motors have 95°C thermal switches inside the motor. If the linear motor exceeds the temperature switch’s rated temperature, the switches will open. When connected and programmed properly to the control system, the open switch will shut down the linear motor.

Higher temperature switches are available. Please consult the factory for these options.

 

Q: WHAT VOLTAGE DRIVES CAN BE USED WITH MOOG LINEAR MOTORS?
Servo drives that use 240 or 480 VAC or less are acceptable for use with Moog linear motors. Using voltages less than 208 VAC will result in a reduction in performance from the published peak speed and dynamic response.

 

Q: HOW MUCH SIDE LOAD CAN BE APPLIED TO THE LINEAR MOTOR SHAFT?
Side load should be kept below 25 lbf at all times.

 

Q: CAN THE LINEAR MOTOR SHAFT ROTATE?
Linear motors with an LP type encoder are free to rotate. This does not affect the ability of the linear motor to produce force. A rotating shaft linear motor can only be accomplished with a position feedback sensor that would allow shaft rotation. Continuous rotation of the shaft could decrease the bearing life of the linear motor.

 

Q: CAN THE LINEAR MOTOR BE USED TO CONTROL FORCE?              
Moog linear motors work very well and accurately in a closed loop force servo system for controlling force. Employing a force transducer to provide feedback will result in the most accurate force control system. Controlling force without a closed loop force servo control tends to yield poor accuracy. It is possible to increase the accuracy of open loop force control by adding compensation tables (position, temperature, speed) to the control loop.

 

Q: CAN MOOG PROVIDE MODIFIED LINEAR MOTOR SOLUTIONS?
Yes, Moog engineers can work with you to design a modified linear motor solution to meet your project's needs. Simply contact us to get started.

 

Q: HOW DOES TOTAL COST OF OWNERSHIP COMPARE BETWEEN MOOG LINEAR MOTOR SOLUTIONS VERSUS HYDRAULIC, PNEUMATIC OR ELECTRIC ROTARY SOLUTIONS?
Compared to the alternatives, Moog's linear motor solution provides a much simpler and lower cost design over lifetime of the system. This is because linear motors operate with much fewer system components (no valves, pumps, hoses, etc.) which all need extensive maintenance & require machine downtime. Moog's linear motors generally only need a little oil every 6 months.

 

Q: ARE MOOG LINEAR MOTORS SPLASH-PROOF OR WATER-PROOF?
Not at this time. Please contact us regarding your splash-proof or water-proof requirements.

 

Q: WHAT CABLES ARE REQUIRED FOR LINEAR MOTOR SYSTEMS?
Motor power cables, encoder signal cables, and temperature switch cables.

 

Q: DOES MOOG PROVIDE EMI AND SYSTEM NOISE REDUCING CAPABILITIES?
Moog provides a selection of line filters and chokes that are matched to the drives and the motors to control EMI and noise in the system for reliable operation.

 

Q: CAN THE MOOG SYSTEM BE USED ON MULTIPLE AXIS SYSTEMS?
Yes, Moog Axis Control Software (MACS) offers a state-of-the-art development environment for implementing demanding motion control functions using the IEC 61131 standard for development. This is a PC-based commissioning system that develops motion control algorithms and allows the user to control multiple axis in coordinated motion.

 

Friction

Q: WHAT IS THE STATIC AND DYNAMIC FRICTION DRAG FORCE OF THE MOTORS?
Static friction is greatly variable since it is time dependent. It ranges from just greater than dynamic friction at very small dwell times at a stopped position, to approximately twice the dynamic friction when left stationary for several days.

 

Q: CAN YOU CHARACTERIZE THE SOURCE AND VARIABILITY OF THE NORMAL FORCE THAT CREATES THE FRICTION DRAG FORCE?
The normal force that creates the drag is primarily based on two phenomena:

  1. The magnetic attraction between the shaft and the stator causes the majority of the drag force. This force is dependent on the magnetic strength of the magnets, the area of interaction of the magnets and the stator, and the distance from “on center” the shaft is in the stator. However, there are variations due to physical limitations. The bearings cannot be operated at zero clearance. In addition, the shaft and bearing diameters must have a tolerance. There is also a variation in the magnetic center of the shaft vs. the physical center of the shaft based on the tolerance build up in the production of the shaft. All of these clearances and tolerances must be accommodated within a very small air gap in order to obtain the high thrust capability of Moog linear motors.
  2. The tightness of the wipers in the groove between the end plates and the shaft causes an additional drag force. This force has a variation dependent on the tolerances of the shaft, end plate, wiper and motor assembly.

 

Detent Force

Q: THE MOOG BROCHURE LISTS A SPECIFICATION "DETENT FORCE (PEAK)." HOW IS THE SPECIFICATION DEFINED AND MEASURED?
This specification is defined as the peak (as opposed to peak to peak) variation in the drag of the motor. The detent, as well as the drag, is measured by pulling on the shaft with the motor de-energized from one end of stroke to the other end of stroke. A force transducer reports the force and a position sensor reports the linear position of the shaft. A chart is then made of the force vs. position. The drag force and the detent force must not exceed the specifications. This test is performed on all motors as part of the acceptance test.

 

Physical Tolerances

Q: WHAT ARE THE TOLERANCES OF THE END OF THE MOTOR SHAFT, LESS THE END STOP? (FLATNESS AND PERPENDICULARITY TO THE SHAFT OUTSIDE DIAMETER)
Perpendicularity -0.002 to OD, flatness is not controlled separately.

 

Q: WHAT IS THE NOMINAL CLEARANCE AND TOLERANCE OF THE SHAFT-TO-BEARING INTERFACE?
Bearing ID dimension is 2.002 +.0000 / - .0005 inch
Shaft OD dimension is 1.999 +.0010 / - .0000 inch
Clearance is therefore .0030 - .0015 inch

 

Shaft Bearings

Q: WHAT BRAND AND AMOUNT OF OIL SHOULD BE ADDED TO MAINTAIN GOOD OPERATION OF MOOG LINEAR MOTORS?
We generally recommend 5 ml of Anderol® 465 be added to oil port every 6 months. This can vary based on individual application usage. If you feel your environment or usage rate is harsh, then add oil more frequently. We do NOT recommend a large reservoir pool of oil be connected to oil port as too much oil will cause different issues. 

 

Q: CAN MOOG PROVIDE ANDEROL® 465 MAINTENANCE OIL TO ME?

Yes, we can provide Anderol® 465 maintenace as long as your shipping address is within the USA. Other locations worldwide need to source locally due to International shipping regulations. Contact www.anderol.com for local sourcing outlets outside of the USA.

 

Q: WHAT IS THE ESTIMATED LIFE OF THE CURRENT SHAFT BEARINGS?
In excess of 100 million inches of travel through empirical testing with no side load applied.

 

Q: WHAT ARE THE SIDE LOAD LIMITATIONS OF THE CURRECT BEARING SYSTEM?
We normally recommend that side loading be kept below 25 lbf when the shaft is within 10 inches of the motor face. For longer strokes, the maximum side load should be decreased.

 

Performance

Q: WHAT CAN WE EXPECT FOR VARIATIONS IN FORCE CONSTANT VS. POSITION?
Force constant varies by position primarily due to detent force and variation in drag. These two forces are mostly independent of the force being generated by the motor. As a result, the force constant as much as the detent force and drag vary.

 

Q: CAN MOOG LINEAR MOTORS PRODUCE MORE FORCE AND SPEED THAN SPECIFIED?
Yes, by coupling two linear motors side-by-side, the force can be increased dramatically (~2x). Please contact us if you need even more performance.

 

Q: CAN LINEAR MOTORS PRODUCE PEAK FORCE AND MAXIMUM SPEED AT THE SAME TIME?
No, linear motors cannot product peak force and maximum speed at the same time. Download the datasheets below to see the force / velocity curves for performance under different current and cooling conditions.

Download Linear Motor Datasheet >
Download Compact Linear Motor Datasheet >

 

Q: HOW MUCH CONTINUOUS DUTY FORCE CAN MOOG LINEAR MOTORS PRODUCE?
From 0 – 710 lbf-f (0 - 3,158 N); with high end performance achieved by using standard available fan or liquid cooling options mounted on the linear motor.

 

Encoder

Q: WHAT IS THE RESOLUTION OF THE AVAILABLE ENCODERS?

  • LPA - Incremental - Hall - A Quad B - 5,080 counts/inch
  • LAF - Absolute - Optical EnDAT 2.0 - 508,000 counts/inch
  • LCA - Incremental - Optical - A Quad B – 5,080 counts/inch
  • LCB - Incremental - Optical A Quad B - 25,400 counts/inch
  • LCC - Incremental - Optical A Quad B - 50,800 counts/inch
  • LCD - Incremental - Optical A Quad B - 254,000 counts/inch
  • LCE - Incremental - Optical - SIN/COS – Depends on interpolation and driver controller

 

Q: CAN YOU EXPLAIN THE OPERATIONS PRINCIPLE FOR LP ENCODERS?The basic operation principle is that it measures the magnetic field shape and does not depend much on the intensity to determine the position within the magnetic cycle. This increases the resolution and accuracy capability of the technology.

 

Q: IS AN ABSOLUTE VERSION ENCODER AVAILABLE? IF SO, WHAT IS THE ESTIMATED RESOLUTION AND ACCURACY?
Yes, an absolute encoder is now available. The designation is “LAF.” The resolution is 508 K counts / inch.

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