Linear Servo Motors

Overview

Linear servo motors, also known as brushless linear motors, are high-precision direct drive motors designed for closed-loop positioning applications requiring exceptional accuracy and repeatability. Available in ironless and iron-core configurations, these 3-phase motors achieve speeds up to 240 in/sec [6 m/s] and forces up to 3105 lbs [13813 N] peak.

When paired with a linear encoder for position feedback and a servo amplifier, these motors deliver precise control of position, velocity, and acceleration. The coil assembly can be commutated trapezoidally using integral Hall effects or sinusoidally using software commutation with the appropriate motion controller.

How Linear Servo Motors Work

Linear servo motors operate on the same electromagnetic principle as rotary brushless servo motors, but produce linear motion instead of rotation. The system consists of a stationary magnet assembly and a moving coil assembly that interact to create force.

When three-phase current is applied to the coil windings, electromagnetic forces are generated between the coil and permanent magnets. By electronically switching (commutating) the current between the three phases, continuous linear motion is produced. A linear encoder continuously monitors position and sends feedback to the controller, which adjusts current to maintain precise position, velocity, and acceleration.

The absence of mechanical transmission components like lead screws or belts eliminates backlash, wear, and maintenance while enabling high speeds and accelerations with exceptional positioning accuracy.

Motor Configurations

Ironless Linear Servo Motors (BLDM Series)

The ironless design features an encapsulated coil assembly that moves through a U-shaped magnet track gap. A customer-supplied bearing system maintains a 0.025″ [0.63 mm] air gap clearance. There is no magnetic attraction between the coil and magnets.

Advantages:

• Zero Cogging – Smooth motion at all speeds with no force ripple
• Low Moving Mass – Enables high accelerations of lighter loads
• High Speed Capability – Up to 240 in/sec [6 m/s]
• Unlimited Stroke – Modular magnet tracks extend to any length
• Multiple Coils – Several coil assemblies can operate on one magnet track
• No Attraction Force – Reduces bearing load requirements

Performance Range:

• 6 different cross sections (BLDM-A through BLDM-F)
• 5 coil assembly lengths
• Continuous force: 1.2 – 173 lbs [5.3 – 771 N]
• Peak force: 3.6 – 517 lbs [16 – 2300 N]

Construction:

• Magnet Assembly: U-shaped nickel-plated steel back iron with neodymium magnets bonded to parallel plates. Available in widths from 0.82″ to 1.73″ [20.8 – 44 mm]. Single-piece assemblies up to 40″ [1036 mm]; longer strokes use modular sections.
• Coil Assembly: 3-phase copper windings, aluminum mounting bracket, and optional Hall effect board vacuum-encapsulated in epoxy. Maximum single-piece lengths: 5.3″ [134.6 mm] for BLDM-A/B, 10.1″ [256.5 mm] for BLDM-C, 14.9″ [378 mm] for BLDM-D, 17.3″ [439 mm] for BLDM-E, 20.0″ [508 mm] for BLDM-F.

Iron-Core Linear Servo Motors (BLSM Series)

The iron-core design features an encapsulated coil assembly with steel laminations that moves over a flat magnet track. A customer-supplied bearing system maintains a 0.025″ [0.63 mm] air gap. There is magnetic attraction between the coil and magnets.

Advantages:

• High Force Density – Greater thrust per unit size than ironless designs
• Heavy Load Acceleration – Ideal for moving large masses at high speeds
• Magnetic Preload – Attraction force can preload bearing systems
• Unlimited Stroke – Modular magnet tracks extend to any length
• Multiple Coils – Several coil assemblies can operate on one magnet track
• Reduced Cogging – Design features minimize force ripple

Performance Range:

• 7 different cross sections (BLSM-1 through BLSM-7)
• 7 coil assembly lengths
• Continuous force: 18 – 1164 lbs [80 – 5179 N]
• Peak force: 48 – 3105 lbs [213 – 13813 N]

Construction:

• Magnet Assembly: Flat nickel-plated steel back iron with neodymium magnets bonded to one side. Available in widths from 2.5″ to 10.5″ [63.5 – 267 mm]. Single-piece assemblies up to 39.8″ [1010.9 mm]; longer strokes use modular sections.
• Coil Assembly: 3-phase copper windings around steel laminations with optional Hall effect board, vacuum-encapsulated in epoxy. Maximum single-piece lengths: 6.4″ [162.6 mm] for BLSM-1, 11.8″ [299.7 mm] for BLSM-2, 17.2″ [436.9 mm] for BLSM-3, 22.6″ [574 mm] for BLSM-4, 28″ [711.2 mm] for BLSM-5, 33.4″ [848.4 mm] for BLSM-6, 38.8″ [985.2 mm] for BLSM-7.

Ironless vs. Iron-Core Comparison

Key Components

Magnet Assembly (Stationary or Moving)

Precision-assembled neodymium permanent magnets bonded to nickel-plated steel back iron. Pre-drilled mounting holes enable easy installation. Modular sections can be joined end-to-end for unlimited stroke length.

Coil Assembly (Moving or Stationary)

Three-phase copper windings vacuum-encapsulated in thermally conductive epoxy for heat dissipation and mechanical protection. Optional Hall effect sensors provide commutation feedback for trapezoidal drive systems.

Position Feedback

Linear encoder (customer-supplied or H2W-integrated) provides position feedback for closed-loop servo control. Typical resolution ranges from 0.1 to 5 microns.

Control & Commutation

Trapezoidal Commutation: Uses integral Hall effect sensors (3-sensor board) for simple 6-step commutation. Compatible with standard brushless motor drives.

Sinusoidal Commutation: Uses encoder feedback with software-based field-oriented control for smoother operation and higher efficiency. Requires servo amplifier with sinusoidal commutation capability.

Required Electronics:

• Motion controller or PLC with servo control capability
• Servo amplifier (brushless/3-phase) matched to motor specifications
• Linear encoder for position feedback
• Motor power cable and encoder cable

Performance Specifications

Speed: Up to 240 in/sec [6 m/s]

Acceleration: Up to 9 g’s (iron-core with heavy loads)

Force Output:

• Ironless: 1.2 – 173 lbs [5.3 – 771 N] continuous, 3.6 – 517 lbs [16 – 2300 N] peak
• Iron-core: 18 – 1164 lbs [80 – 5179 N] continuous, 48 – 3105 lbs [213 – 13813 N] peak

Air Gap: 0.025″ [0.63 mm] typical

Positioning Accuracy: Dependent on encoder resolution (typically ±0.1 to ±5 microns)

Duty Cycle:

• Continuous (100%): Listed continuous force ratings
• Peak (10%): Listed peak force ratings

Design Flexibility

Multiple Coil Configuration: Several coil assemblies can operate independently or coupled together on a single magnet track to increase total force output. Spacing between coils must maintain specific pole pitch multiples (1.8″ for ironless, 2.4″ for iron-core).

Moving Magnet Option: While most applications use a moving coil with stationary magnets, H2W can provide moving magnet configurations where cable management is critical. This allows the coil assembly to remain stationary while the magnet track moves.

Custom Configurations: Motors can be customized for specific force, stroke, mounting, and packaging requirements. Consult factory for custom designs.

Applications

Linear servo motors excel in precision positioning applications requiring high speed, accuracy, and repeatability:

Manufacturing Automation:

• Pick and place machines
• High-speed assembly equipment
• Parts transfer systems
• Packaging machinery

Inspection & Testing:

• Vision inspection systems
• Coordinate measuring machines (CMM)
• Wafer inspection equipment
• Automated optical inspection (AOI)

Material Processing:

• Laser cutting and marking systems
• Water jet cutters
• CNC machining centers
• 3D printing and additive manufacturing

Semiconductor & Electronics:

• Die bonding equipment
• Wire bonding machines
• Cleanroom automation
• Wafer handling systems

Medical & Laboratory:

• Blood analyzers
• DNA sequencers
• Automated microscopy
• Sample handling systems

Advantages & Limitations

Installation Requirements

Air Gap Maintenance

Critical 0.025″ ± 0.005″ [0.63 ± 0.13 mm] air gap must be maintained between coil assembly and magnet track throughout entire stroke. Use precision shims during installation to set proper clearance. Remove shims before operation.

Bearing System

Customer-supplied linear bearing system must maintain air gap specification and support payload. For iron-core motors, bearing system must also support magnetic attraction force between coil and magnets.

Modular Magnet Installation

Magnet track sections install end-to-end with no spacing. Mounting hole patterns repeat across joining ends. Pole alignment between sections is self-registering when mounted to flat base plate.

Why Choose Linear Servo Motors

Linear servo motors eliminate mechanical transmission components, providing direct-drive precision without backlash, compliance, or wear. The brushless design requires no maintenance while achieving speeds to 240 in/sec and accelerations to 9 g’s. Available in ironless configurations for zero-cogging smooth motion or iron-core designs for maximum force density. Modular magnet tracks scale to unlimited stroke lengths, and multiple coil assemblies can combine for higher thrust. Standard 3-phase brushless amplifiers simplify integration into existing motion control systems.

Ordering Information

Ironless motors available in 6 frame sizes (BLDM-A through F) with 5 coil lengths. Iron-core motors available in 7 frame sizes (BLSM-1 through 7) with 7 coil lengths. Custom stroke lengths, mounting configurations, and motor specifications available. Consult factory for detailed specifications, CAD models, and application assistance.

Product Selection Charts

Ironless Linear Servo Motors (BLDM Series) [Product number chart showing BLDM-A through BLDM-F series with varying coil lengths]

Iron-Core Linear Servo Motors (BLSM Series) [Product number chart showing BLSM-1 through BLSM-7 series with varying coil lengths]