This paper describes a mobile auto-focus actuator for phone cameras built with a rotary voice coil motor. The design enables zero holding current to maintain the lens module in the focusing position, meaning the focused position can be held without continuous power.

Xeryon contrasts ultrasonic piezo motors with electromagnetic motors, stating: "Electromagnetic motors offer an alternative but require continuous power to hold position and take up (much) more space." By contrast, it notes that ultrasonic piezo technology solves these issues, implying that the piezo motor can hold position without the continuous power that electromagnetic solutions need.

PI describes one of the fundamental properties of its piezo motors: "Piezo Motors are intrinsically vacuum compatible, non-magnetic and self locking at rest, providing long travel compared to traditional piezo mechanisms." It further emphasizes a key advantage: "Self-clamping: Due to the design principle, piezo motors are self-clamping at rest, without the need for a brake mechanism, a decisive advantage in applications that require very stable positioning without servo jitter." This indicates that the motor holds position mechanically at rest rather than via continuous electrical power.

Xeryon describes ultrasonic piezo-based actuators as self-locking: "The ultrasonic motor that drives the actuator is spring-loaded against the actuator rod. This allows the actuator to hold its position without any power consumption or drift, offering reliability and complete stability, unmatched by traditional actuators that continuously consume energy to maintain position." It further notes: "Since the actuator doesn't require power to hold its position, it can maintain stability without consuming energy."

PI describes its piezoceramic linear motors as intrinsically self-locking: "An essential requirement then is that the units be self-locking when not under power... Piezoelectric ceramic actuators however, acting as solid-state analog positioning elements, are not subject to these limitations." The article adds: "This means that when powered down, the runner is held in place by the friction resulting from the high internal preload and can only be moved from its position by very high external forces" and summarizes that "The drive is intrinsically self-locking and does not expend energy to hold a position."

APC notes that piezoelectric motors are energy efficient in part because they can hold position without power: "Piezoelectric motors can achieve micrometer- or nanometer-level resolution and are energy-efficient, maintaining position without electrical power." This explicitly states that a piezo motor can maintain its mechanical position without needing continuous electrical current.

Newport’s product page highlights that its piezo motor stages offer a "self-locking" capability: "Once in position, the stages hold their position without power, eliminating heat generation and position drift due to power fluctuations." It notes that this power-off holding characteristic is intrinsic to the piezo motor drive mechanism. This is presented as a differentiator from conventional electromagnetic stages that require continuous current to hold position.

Discussing a specific type of piezo motor, the article states: "A Piezo LEGS motor can be very energy efficient compared to conventional motor alternatives. It does not consume any power in hold position, and the motor does not generate any heat." This indicates that this piezoelectric motor design holds its position mechanically with zero power draw when not actively moving.

The datasheet-style description of the LT40 piezo motor states: "The motor has no backlash and draws no power in the hold position." It further notes that the actuator is self-locking through its mechanical design, meaning it can maintain a commanded position without continuous power.

In listing limitations of voice coil actuators, Moticont explains: "Because voice coil motors produce force only when current flows through the coil, they cannot hold a position without continuous power unless an external brake or mechanical holding device is used." It further clarifies that they are non‑cogging and have no detent torque, which is why they do not provide inherent holding force at standstill.

Actronic Solutions describes the voice-coil motor as "the technical use of the Lorentz-Force-Principle: the force of a current carrying wire in the magnetic field of a permanent magnet is proportional to the field strength and the current." It explains that by changing current polarity, the force direction reverses, making the VCM a bidirectional actuator. Because the generated force is strictly proportional to current, the actuator cannot apply or maintain force in a given direction – for example, to hold a lens off its spring-rest position – without a corresponding continuous current.

Newport’s technical note describes that a voice coil motor "generates a force that is proportional to the current" and emphasizes dynamic operation: "Since there is no preferred rest position or detent, a VCM cannot hold a position without current; position must be actively controlled by applying the required holding current." This directly addresses the need for continuous current to maintain a non-rest position.

PiezoMotor contrasts its motors with electromagnetic types: "Piezoelectric motors are based on friction and are inherently self-locking when the drive signal is removed." It continues: "When the motor is stopped and power is turned off, the frictional coupling maintains position without any energy consumption, unlike electromagnetic motors which typically require current to hold position."

In describing electromagnetic focus drives in microscopes, Olympus notes that voice-coil type focus systems use a moving coil in a magnetic field to shift the objective or stage, with position maintained through active control. The documentation states that holding a focus position against gravity and other loads requires the drive to apply force, which is provided by regulated current in the coil. When power is removed, the movable element returns to its mechanical rest or is otherwise free to move unless restrained by brakes or friction, unlike self-locking piezo-driven stages.

An article on a rotary piezoelectric motor explains: "The motor design enables accurate angular positioning and the ability to maintain any set position without the need for applied power, characteristics that are essential for many medical devices and high-tech applications." It also notes that the motor "consumes zero power in hold position while still providing significant torque." This directly supports that this piezo motor type holds position without continuous power.

A VCM autofocus camera module uses a voice coil motor to move the lens quickly and silently for sharp focus. The page describes VCM autofocus modules as using current to move the lens, implying an actively driven actuator rather than a mechanically latched one.

In discussing piezo motors for mobile camera optical zoom and autofocus, New Scale explains that piezo motors use piezoelectric ceramic elements to create ultrasonic vibrations that generate linear motion. It emphasizes benefits such as high resolution and the ability to maintain precise positions, and in other product literature the company notes that many of its ultrasonic piezo motors are inherently self-locking when unpowered, unlike electromagnetic solutions that require current to hold position.

Thorlabs describes its voice coil actuators as devices where force is proportional to current and position is determined by the balance of Lorentz force against a spring or load. It notes that these actuators are typically used with closed-loop controllers that continuously drive current to achieve and hold a given position. When current is set to zero, the internal spring or load returns the actuator to its mechanical equilibrium position, meaning they do not self-lock in an arbitrary position without power.

The page explains that a dedicated driver supplies current to the voice coil motor, and increasing or reversing the current moves the lens forward or backward. It describes the autofocus loop as continuously controlling the VCM module to reach and maintain the target focus position.

The article explicitly states that VCM elements need constant power to stay in position and do not mechanically lock like traditional focusing systems. It further says the focus group settles into its rest position when power is removed.

The article says VCMs are used in smartphone autofocus systems and work by moving the lens forward or backward with electromagnetic force. It presents VCMs as direct-drive actuators for autofocus, which aligns with the need for driven current rather than passive mechanical retention.

In many smartphone camera modules, a voice coil motor produces force approximately proportional to coil current, so maintaining a non-rest lens position typically requires continuous drive current unless the design includes a special mechanical latch, magnetic bias, or other zero-hold mechanism. This is the general contrast with piezoelectric actuators, which in many implementations can hold position with little or no continuous power depending on the mechanism.

The page explains that a VCM uses current through a coil inside a magnetic field to move the lens along the optical axis. It also says that reducing the current lets a return spring pull the lens back to its resting position, indicating that the actuator is not passively latched at an arbitrary focus point.