Understanding Linear Motors

Table of Contents

What is a Linear Motor?
Bridging Terminology
Basic Types of Linear Motors
     Brushless
     Brush
     Voice Coil
     Linear Stepper
     Linear Induction
     Polynoid
Force Multipliers Based on Duty Cycle
Linear Motor Force
Linear Motor Advantages

What is a Linear Motor?

A linear motor should be considered as a rotary electric motor that has been cut along a radial plane and unrolled. The resulting motor is a direct drive linear electric motor that can generate linear motion without the requirement for pneumatic, hydraulic cylinders, or translation of rotary to linear motion with the use of screws or belts. Linear motors generate linear force while rotary motors generate torque.

Bridging Terminology

Rotary Linear
Torque (lb-in) or [N-m] Force (lbs) or [N]
Velocity (rpm) Velocity (in/sec) or [m/sec]
Acceleration (rad/s2) Acceleration (in/sec2) or [m/sec2]
Duty Cycle (%) Duty Cycle (%)

Basic Types of Linear Motors

As there are different types of AC and DC rotary type motors, there are also various types of linear motors, which include Stepper, AC, and DC:

Test Image Positioning Type Force @100% Duty Force @10% Duty Max Stroke Max Velocity* Max Accel.* Amplifier or Drive Type Bearing Type Options
Brushless (Ironless) Closed Loop 1 - 200 lbs
[5 - 900 N]
3 - 600 lbs
[15 - 2700 N]
Unlimited 240 ips
[6 m/s]
12 g's 3 Phase Brushless Servo, Trapezoidal or Sinusoidal Customer Supplied Air, Water Cooling
Brushless (Iron Core) Closed Loop 15 - 1200 lbs
[60 - 2500 N]
45 - 3600 lbs
[180 - 7500 N]
Unlimited 240 ips
[6 m/s]
12 g's 3 Phase Brushless Servo, Trapezoidal or Sinusoidal Customer Supplied Air, Water Cooling
Brush Closed Loop 4 - 60 lbs
[15 - 275 N]
12 - 180 lbs
[45 - 825 N]
96 in
[2450 mm]
100 ips
[2.5 m/s]
6 g's Brush Type PWM Servo Customer Supplied Stationary Cables, Water Cooling
Voice Coil (Moving Coil) Open & Closed Loop 0.05 - 600 lbs
[0.2 - 4500 N]
0.15 - 1800 lbs
[0.6 - 13500 N]
4 in
[100 mm]
50 ips
[1.27 m/s]
20 g's Linear/PWM Servo Customer Supplied, Linear Bushing Mounting, Windings, Transducers
Voice Coil (Moving Magnet) Open & Closed Loop 0.05 - 600 lbs
[0.2 - 4500 N]
0.15 - 1800 lbs
[0.6 - 13500 N]
4 in
[100 mm]
50 ips
[1.27 m/s]
20 g's Linear/PWM Servo Customer Supplied, Linear Bushing Mounting, Windings, Transducers
Single Axis Stepper Open & Closed Loop 2 - 50 lbs
[9 - 225 N]
2 - 50 lbs
[9 - 225 N]
144 in
[3.6 m]
80 ips
[2 m/s]
1 g Microstepping Air, Roller Mounting, Cables, 2 and 4 Phase
Dual Axis Stepper Open & Closed Loop 1.5 - 30 lbs
[6 - 140 N]
1.5 - 30 lbs
[6 - 140 N]
20 x 20 in
[0.5 x 0.5 m]
80 ips
[2 m/s]
1 g Microstepping Air Mounting, Cables, 2 and 4 Phase
Linear Induction Open Loop 1 - 80 lbs
[4 - 360 N]
5.5 - 440 lbs
[22 - 1980 N]
Unlimited 1800 ips
[45 m/s]
2 g's AC Line Voltage, Variable Frequency, Vector Drive Customer Supplied Air Cooling
Polynoid Open Loop 1 - 9 lbs
[4 - 40 N]
5.5 - 49.5 lbs
[22 - 220 N]
120 in
[3 m]
270 ips
[6 m/s]
2 g's AC Line Voltage, Variable Frequency, Vector Drive Customer Supplied Air Cooling

* = Max values depend on motor size and bus voltage available. Please contact factory to discuss application requirements.

Brushless

The DC brushless linear motors provide non-contact operation that ensures maintenance-free operation. They are capable of high acceleration motion and high speed profiles, and are available in both iron core and ironless (cog-free) models. The brushless linear motors motors can be driven using standard 3-phase brushless servo amplifiers. They can attain an acceleration of up to 12 g’s, and speeds in excess of 200+ inches per second [5+ m/s].

Brush

DC brush linear motors are perfect for long stroke, closed or open loop servo, linear motion applications. They can be used at speeds up to 100 in/second [2.5 m/sec] and as low as 1 in/second [25 mm/sec]. When coupled with a linear encoder, DC brush linear motors are capable of very precise position, acceleration control, and velocity.

Voice Coil

DC voice coil actuators are suitable for short stroke (typically less than 2 inches) closed loop servo applications. They can fit into small spaces due to their compact sizes and have very low mechanical and electrical time constants. The low moving mass facilitates high accelerations of light payloads. They are available in both moving magnet and moving coil versions.

Linear Stepper

Linear stepper motors are used in both closed loop and open loop positioning applications. As the positioning is integrated into the platen and forcer, no extra feedback devices are required, which reduces the total cost of a system. Servo tuning is not necessary for open loop operation. Multiple forcers can function on a single platen. Speeds up to 100 in/second [2.5 m/s] and acceleration of 1 g are typical with linear steppers. Both single-axis and dual-axis versions are available.

Linear Induction

The flat AC linear induction motor (LIM) is typically operated directly off of three-phase line voltage, with a modifiable frequency, or vector drive if speed control is needed. Accelerations of up to 1 g with speeds in excess of 1800 in/second [45 m/s] can be achieved with LIMs. They are perfect for high speed, long travel applications moving heavy payloads.

Polynoid

The tubular AC linear induction motor (polynoid) is usually operated directly off of single or 3-phase line voltage. Accelerations more than 1 g can be achieved with polynoids. They are perfect for short stroke, low duty cycle applications and can be used to substitute air cylinders when compressed air is not available.

Force Multipliers Based on Duty Cycle

Basic Types of Linear Motors Continuous Force/ Motor Area lbs/in2 [N/m2] Peak Force/ Motor Area lbs/in2 [N/m2]
AC Linear Motors 0.2 1
DC Linear Motors 2.5 7.5
Linear Stepper Motors 2.5 7.5

Linear Motor Force

Linear motors produce force (measured in Newtons or pounds) along a straight line axis to move its payload. Each type of motor offers varying force levels.

Force depends upon duty cycle, which is specified as a percentage:

Linear Motor Advantages

The main advantages of the linear motor are as follows:

  • High speeds: Speeds to 1800 in/second [45 m/second]
  • Faster acceleration: From 1 to 10 g’s; this leads to shortened cycle times and improved productivity for the customer
  • Very repeatable: Repeatability to 0.00004 in [1 µm]
  • High stiffness: Direct drive linear motors offer higher stiffness than ball screw/lead screw systems
  • No backlash: A direct drive approach has no backlash such as obtained in leadscrews, gears, belt drives, and pinions
  • Very smooth operation: Linear packages provide smooth operation due to the elimination of mechanical linkages
  • Highly accurate: Accuracy to 0.00004 in/ft [1 µm/305 mm]
  • Non-contact parts: This reduces friction and wear of components, reducing the customer’s maintenance
  • Low maintenance: This helps to reduce the customer’s total costs
  • Long life: Indefinite life expectancy under regular operating conditions can be expected, thanks to the simplicity and part reduction
  • Unlimited stroke: Stroke lengths are not restricted as with ball screws. It is easy to widen the stroke by merely incorporating another section

This information has been sourced, reviewed and adapted from materials provided by H2W Technologies.

For more information on this source, please visit H2W Technologies.

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback
Submit