A Comparison between Voice Coil Actuators vs Solenoids

Table of Content

Introduction
What is a Voice Coil Actuator?
What is a Solenoid?
Comparison
Should I Select a Voice Coil Actuator or a Solenoid?

Introduction

One frequently asked question is whether to use solenoids or voice coil actuators for small displacement motion control applications. This article explains the main differences between each product and why one might be chosen over the other for specific applications.

A non-commutated DC linear actuator, generally known as a voice coil, is capable of a displacement in excess of 5”. Additionally, voice coil actuators have a constant force over the stroke and can move bi-directionally. They can be used for closed loop position and force applications.

While a solenoid is capable of generating high forces at extremely short strokes, it needs a spring return as they are operated unidirectional and the force output declines quickly through the total displacement, and therefore are generally only used for short strokes, not typically longer than 0.5 in. A solenoid is typically used in the simple opening or closing of a valve or switch, but not typically used for position or force control applications.

A force is generated by a voice coil based on an interaction of a current carrying conductor in a permanent magnetic field.

A force is generated by a solenoid based on an electromagnetic field produced by a current carrying conductor.

What is a Voice Coil Actuator?

Voice coil actuators or non-commutated DC linear actuators consist of a coil assembly and a permanent magnetic field assembly (ferrous steel and permanent magnets). A force vector perpendicular to the direction of the current is generated when the current flowing through the coil assembly interacts with the permanent magnetic field. The polarity of current flowing through the coil can be changed to reverse the force vector.

The voice coil generates the force, which is proportional to the cross product of the current flowing through the magnetic flux and the coil in the permanent magnetic field, as dictated by Lorentz’ force equation. Either the permanent magnetic field assembly or coil assembly can be used as the moving member in a voice coil actuator.

The force produced is relatively constant throughout the stroke of the actuator, with minor dips at the beginning and end of the travel length.

Typically, voice coil actuators are used in miniature position control, mirror tilting, oscillatory systems, and focusing applications.

What is a Solenoid?

Solenoids consist of a coil that is contained in a movable steel slug or washer and a ferrous steel housing. An electromagnetic field is generated when current is applied to the coil. The amount of force that can be generated by the solenoid is determined by the magnetic field intensity. The force drops to zero and the spring returns it to its extended position when the power is turned off.

Initially, the forces are high, but as the stroke increases the force decreases.

Typically, solenoids are used to open or close valves or open latches, and are either used to apply a holding or latching force.

Comparison

Voice Coil Actuator Solenoid
Force Low to medium High
Stroke 5 inches maximum ¼ inch maximum
Constant Force Yes No
Reversible Yes No
Position/Force Control Yes No
Cost Moderate Low

Should I Select a Voice Coil Actuator or a Solenoid?

A solenoid could be used if the application simply requires opening or closing a valve, but it has certain limitations when it comes to stroke length and force linearity.

Many customers try and use a solenoid when a voice coil actuator is the more appropriate solution, because the latter typically costs more than an off-the-shelf solenoid. Some applications need a constant force throughout the travel length, and in these situations a solenoid is not sufficient due to the diminished force through the travel, while a voice coil actuator provides continuous force. This is especially important in oscillatory systems.

Another benefit provided by the voice coil is force control, without a feedback device, as the force output (at any position in the stroke) is directly proportional to the current input.

Generally, this type of actuation lends itself to a higher force density and attains higher strokes and forces in a smaller package size to the solenoid counterparts.

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

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

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