Application NotesTechnical Documentation & Guides

Overview

PBA Systems direct drive linear motors couple the motor force straight to the payload, so there's no ball screw, belt, or gearbox in between. That gets you zero backlash, no mechanical wear, very high acceleration, and positioning down to the nanometer. Picking the right motor comes down to matching force, speed, and thermal behavior to what the application actually needs.

Force and Speed Requirements

The two numbers that drive the choice are continuous force and peak force at your target speed. A linear motor gives you full force at any speed up to the thermal limit, which a rotary-to-linear conversion can't do:

• 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 makes both ironless (U-channel) and ironcore (flat) motors. Ironless has no cogging and no attractive force between forcer and magnets, which is what you want for precision work. Ironcore packs more force per unit area but brings cogging and magnetic pull with it. Go ironless for nanometer positioning, ironcore when you need raw force on an industrial machine.

Thermal Management

Continuous force is capped by heat, not by the magnets. The coil dumps heat (P = I²R) that has to go somewhere. If you need more continuous force, a liquid-cooled forcer can run at 2-3× the air-cooled rating. And make sure the mounting surface actually conducts heat away from the motor.

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 short-stroke linear motors with very smooth, controllable force. PBA Systems voice coils show up everywhere from hard disk drive head positioning to active vibration isolation. Construction is just a coil and a magnet, and force tracks current linearly, so they're easy to control for precision force work and short-stroke moves.

Voice Coil Operating Principles

A voice coil runs on the Lorentz force: push current through a coil sitting in a magnetic field and you get a force proportional to that current. The relationship is linear (F = BLI, where B is flux density, L is wire length, and I is current), which is what makes voice coils 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

Drive a voice coil with a linear current amplifier (servo drive) that handles four-quadrant operation. For force control, run it in current (torque) mode with a simple proportional controller. For position control, add an encoder or LVDT and close a PID position loop around it. Copley Controls servo drives work well here.

Mechanical Integration

A voice coil only makes axial force. It gives you no lateral guidance, so a separate bearing system (flexures, air bearings, or linear guides) has to hold every other degree of freedom. For short-stroke precision, flexures are the usual pick since they add no friction or hysteresis. Just keep the bearing stiffness below what the voice coil can push against.

Typical Applications

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

Related Products

VCA Series • VCM Series

Overview

Nanometer positioning is a whole-system problem. Every part (motor, bearing, feedback, structure, controller) has to be built to keep error down, because any one of them can blow the budget on its own. PBA Systems ironless linear motors give you the zero-cogging, smooth motion to start from, but the motor alone won't get you there.

Error Budget Analysis

Set the accuracy you need first, then budget an error allowance 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 get you the best accuracy (sub-nanometer) but they're pricey and fussy about their environment. Optical encoders with interpolation (Heidenhain, Renishaw) hit practical nanometer resolution for a lot less. Under 10nm, look at laser encoders or capacitive sensors, which give you high resolution and high bandwidth at the same time.

Environmental Control

At these scales the environment runs the show. Steel expands 12µm/m/°C, so a 0.001°C swing drifts you 12nm per mm of structure. You need vibration isolation, passive or active. Acoustic noise off fans, pumps, and HVAC can ring structural resonances too. Enclose the system, or put it in a controlled room.

Typical Applications

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

Related Products

FLU Series (Ironless) • VCA Series • Custom Stages