Application NotesTechnical Documentation & Guides

Overview

PBA Systems direct drive linear motors eliminate mechanical transmission elements (ball screws, belts, gearboxes) by directly coupling the motor force to the payload. This provides zero backlash, no mechanical wear, extremely high acceleration, and nanometer-level positioning capability. Selecting the right linear motor requires matching the force, speed, and thermal characteristics to your application requirements.

Force and Speed Requirements

The primary selection criteria are continuous force and peak force at the required speed. Unlike rotary-to-linear conversion systems, linear motors provide full force at any speed up to the thermal limit:

• Continuous force: Limited by thermal dissipation of the forcer coil
• Peak force: Available for short durations (typically 3-5× continuous)
• Speed: Determined by back-EMF voltage vs. available bus voltage
• Acceleration: F = m × a (total moving mass × desired acceleration)
• Calculate RMS force for the complete motion profile

Ironless vs Ironcore Motors

PBA offers both ironless (U-channel) and ironcore (flat) linear motors. Ironless motors have zero cogging force and zero attractive force between forcer and magnets, ideal for precision applications. Ironcore motors provide higher force density but exhibit cogging and magnetic attraction. Choose ironless for nanometer positioning and ironcore for high-force industrial applications.

Thermal Management

Linear motor continuous force is thermally limited. Heat generated in the coil (P = I²R) must be dissipated to the environment. For higher continuous force, consider liquid-cooled forcer assemblies, which can provide 2-3× the air-cooled force rating. Ensure the motor mounting surface provides adequate thermal conductivity.

Typical Applications

• Semiconductor lithography
• Precision assembly automation
• High-speed pick-and-place
• Laser processing equipment

Related Products

FLA Series • FLU Series • FLC Series

Overview

Voice coil actuators (VCAs) are limited-stroke linear motors that provide exceptionally smooth, controllable force output. PBA Systems voice coils are used in applications from hard disk drive head positioning to active vibration isolation. Their simple construction (coil + magnet) and linear force-current relationship make them ideal for precision force control and short-stroke positioning.

Voice Coil Operating Principles

A voice coil actuator operates on the Lorentz force principle: current flowing through a coil in a magnetic field produces a force proportional to the current. This linear relationship (F = BLI, where B is flux density, L is wire length, and I is current) makes voice coils inherently easy to control:

• Force is exactly proportional to current (no cogging or detent)
• Bi-directional operation by reversing current polarity
• Stroke range: typically 1mm to 50mm
• Force range: millinewtons to hundreds of Newtons
• Bandwidth: DC to several kHz (limited by moving mass)

Driver and Control Requirements

Voice coils require a linear current amplifier (servo drive) capable of four-quadrant operation. For force control, operate in current (torque) mode with a simple proportional controller. For position control, add an encoder or LVDT and implement a PID position loop. Copley Controls servo drives are well-suited for voice coil applications.

Mechanical Integration

Voice coils generate only axial force—they provide no lateral guidance. A separate bearing system (flexures, air bearings, or linear guides) must constrain all non-axial degrees of freedom. Flexure bearings are preferred for short-stroke precision applications as they introduce no friction or hysteresis. Ensure the bearing stiffness does not exceed the voice coil's force capability.

Typical Applications

• Active vibration isolation
• Precision focus mechanisms
• Force-controlled testing
• Nano-positioning stages

Related Products

VCA Series • VCM Series

Overview

Nanometer-level positioning requires a systems approach where every component—motor, bearing, feedback, structure, and controller—is designed to minimize error sources. PBA Systems ironless linear motors are the foundation, providing zero-cogging force and smooth motion, but achieving true nanometer performance requires careful attention to the entire system.

Error Budget Analysis

Start by defining the required positioning accuracy and allocate error contributions to each subsystem:

• Motor cogging and force ripple (< 0.5% for ironless)
• Encoder/feedback resolution and accuracy
• Bearing straightness and runout
• Structural compliance and thermal drift
• Controller quantization and servo bandwidth
• Environmental vibration and acoustic noise

Feedback Selection for Nanometer Accuracy

Laser interferometers provide the highest accuracy (sub-nanometer) but are expensive and sensitive to environment. Optical encoders with interpolation (Heidenhain, Renishaw) offer practical nanometer resolution at lower cost. For sub-10nm applications, consider laser encoders or capacitive sensors that provide both high resolution and high bandwidth.

Environmental Control

At nanometer scales, environmental factors dominate. Thermal expansion (steel: 12µm/m/°C) causes drift of 12nm per mm per 0.001°C temperature change. Vibration isolation (passive or active) is essential. Acoustic noise from fans, pumps, and HVAC can excite structural resonances. Enclose the system or operate in a controlled environment.

Typical Applications

• Semiconductor metrology
• Atomic force microscopy stages
• Optical alignment systems
• Precision manufacturing inspection

Related Products

FLU Series (Ironless) • VCA Series • Custom Stages