"The new focusing design enables the zero holding current required to maintain the lens module in the focusing position as well as the reduction of the module thickness… Since the proposed actuator has the zero holding current, there is no power consumption when actuator is not moving due to frictional locking… Therefore, the developed auto-focusing module needs not continuously supply the voltage to keep the lens focusing position. The result, it can save dramatically power consumption than current method."

"The experimental results show that the actuator has a zero holding current when maintaining the lens in the specified focusing position… the proposed actuator has both a higher power efficiency and an improved positioning repeatability compared to existing VCM actuators."

The DRV201 device is intended for high performance autofocus in camera modules. The device is used to control the current in the voice coil motor (VCM). The DRV201 device is designed to operate from an input voltage supply, VBAT, range between 2.5 and 4.8 V. (From the datasheet context, a VCM autofocus actuator’s position is controlled by regulating coil current; when current is removed, the spring return brings the lens back to its rest/infinity position.)

In addition to a very positive size to power ratio, **piezoelectric motors have high holding torque maintained at zero input power**, and they offer low inertia and high acceleration rates. They are small, light, and precise, and can provide motion down to nanometer steps.

"A USM's rotor possesses a tiny amount of inertia, a rapid response at the microsecond level, self-locking, and high holding torque." The review explains that ultrasonic motors "may reach a stable speed in a few milliseconds and stop even faster due to friction between the rotor and stator" and notes their "self-braking" behavior in multi-DOF designs.[2]

The ability of **piezo motors to produce a holding force or torque when there is no input power** rules out the need for an external brake. In many cases, **the holding force of a piezo motor will be greater than the stall force, by about ten percent**. The stall force is the maximum force a motor can hold while running, while the holding force is the maximum load a motor can hold while powered-down.

"The new focusing design enables the zero holding current required to maintain the lens module in the focusing position… For the auto-focusing actuator using the inclined cam, the self-locking condition maintaining the lens module in the focusing position is to be ensured when the current turns off… Since the proposed actuator has the zero holding current, there is no power consumption when actuator is not moving due to frictional locking."

Physik Instrumente describes 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 states: "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."[7]

PICMAWalk motors are **self-clamping**, i.e. **at rest or in steady state mode, they automatically hold the position without any need for power**. When large optics, detectors or camera set-ups need to be positioned with nanometer precision, it can be beneficial to cut the actuator power once the fine positioning process is complete. The space-tested PICMA actuators are highly reliable, providing **60 N power-off holding force**.

Tamron explains its ultrasonic motors used in autofocus lenses: "Ultrasonic motors having high torque, superior quietness and **high holding force under a non-energized state**, is not affected by magnetic force." It notes these USD and PZD piezo-driven actuators are used in Tamron’s AF lens systems.[1]

Piezoelectric motors stand out for their ability to **maintain their position even in the absence of power**, only using energy when necessary for movement. The architecture of this device enables precise control of motion, **the capacity to maintain positions without the need for power**, and the ability to function effectively in applications that are downsized.

"The Voice Coil Motor (VCM) actuator uses a magnetic field to drive the focusing elements… A VCM lens requires power from the camera to hold the focusing lens group in position. This means that when the camera is turned off, or the lens is not attached to the camera, you may notice some noise and movement from the internal components; this is normal and does not affect the performance of the lens."

A Piezo LEGS motor can be very energy efficient compared to conventional motor alternatives. **It does not consume any power in hold position**, since the direct friction coupling between legs and drive rod means Piezo LEGS will operate without backlash. The direct drive also gives **full-force, power-off locking without any power consumption**. The motor is **self-locking due to its frictional clamping**, and it will hold force loads that exceed the stall force by about 10%.

Physik Instrumente’s motion control article states: "Because PILine stages feature an excellent **self-locking mechanism, they do not require extra electrical energy for holding their position**." It highlights that ultrasonic piezo motors can hold position without additional power, reducing energy use and heat generation.[10]

Piezoelectric motors can achieve micrometer- or nanometer-level resolution and are **energy-efficient, maintaining position without electrical current**. With no electric current sent to a piezo motor system, **the device actually maintains its position and is able to stay locked in place due to the science behind the piezo effect**. Piezo motor characteristics mean a **holding force is applied on the object when there is no electrical current**, so this braking device can be used to reduce motion in a system as well.

Ultrasonic-motor.com, a specialist vendor, describes the operating principle: "The **self-locking friction principle allows the position to hold without continuous current, reducing heat." It adds: "Ultrasonic motors are especially useful when ... fast start-stop motion, fine positioning, or **self-locking behavior** is required" and summarises that "piezo motors can provide ... **self-locking operation without power**."[3]

Comparison of piezo motor types lists the parameter **“Holding Without Power”**. For example, **Inertial (Stick-Slip)** motors are described as having **“High” holding without power**, and **Piezo LEGS (Walking)** motors also have **“High” holding without power**, whereas **Ultrasonic Piezo** motors are noted as having **“Low” holding without power**. This table explicitly distinguishes the capability of different piezo motor designs to hold position with zero power.

"But here’s something important to understand: VCM elements need constant power to stay in position. They don’t mechanically lock like traditional focusing systems. This means you might hear a soft ‘clunk’ when you power down or remove the lens. That’s just the focus group settling into its rest position."

Linear Motion Tips explains: "this friction allows **ultrasonic piezo motors to be self-clamping in a power-off condition, capable of producing 2 to 3 N of holding force without heat generation.**" The article contrasts their behavior with other piezo designs and highlights their power-off holding capability.[4]

"A Voice Coil Motor, or VCM, is a high-performance direct-drive motor that converts electrical energy to linear mechanical motion… Voice Coil Motors (VCMs) are currently the standard in lens focus systems of modern cameras due to their unique set of characteristics. VCMs are used in smartphones to shift the lens position to autofocus."

The patented SQUIGGLE motor uses ultrasonic standing wave vibrations in a threaded nut to directly rotate a screw. Additional features include **precise off-power hold and a manual adjustment option by turning the screw**. A comparison table shows that a conventional motor requires **“Continuous to hold position”** with about 200 mW, whereas the **UTAF piezo motor has “Zero power to hold position”**, only using ~100 mW when moving.

Xeryon, a piezo motor maker, describes its ultrasonic piezo actuators: "Systems that once required multiple stages, gear trains, or complex feedback loops can now be built around a single, **self-locking actuator that maintains position without power**." It emphasizes that the motor’s frictional coupling provides stable position holding in a powered-off state.[9]

"Recently, in order to reduce the holding current, a new VCM structure was proposed [2]… As shown in Fig. 1(a), the Lorentz force acting on the moving part of the conventional actuator is affected by the resistant force induced by the two spring plates, and the force is to be larger than the sum of the weight of the moving part and the restoring spring force for the focusing actuation… But this method has high power consumption because of a large holding current required to maintain the lens module in the focusing position."

Liquid lens is much better than a VCM lens when it comes to features and functionalities. ... In a VCM autofocus lens, autofocus is achieved by means of the mechanical movement of the lens. A change in position of the lens with respect to the image sensor is required every time the camera needs to change its focal length. ... A VCM powered autofocus lens is more power hungry than a liquid lens due to regular movement of the motor.

Piezoelectric motors are used in nanoliter infusion pumps and optical-position mechanisms. These motors can provide positioning down to nanometer tolerances. The material is directed by on/off voltage pulsing and mechanical arrangement to make a series of stretches and **position holds**, and so moves like a caterpillar. The motion is both minute and precise, and the motor can **hold positions between steps** without gears or magnetics.

The Wikipedia article on ultrasonic motors notes one of their advantages over traditional motors is that "USMs may reach a stable speed in a few milliseconds and stop even faster due to **friction between the rotor and stator**," which inherently provides holding torque when power is off.[5] Although not explicitly stating "no power," the description of friction-based holding torque underlines the self-locking property used in lens autofocus systems.[5]

"A voice coil motor (VCM) is an actuator that uses Lorentz force generated by electromagnetic force of a coil in a magnetic field of a permanent magnet to linearly move a lens… In conventional auto focusing, the position of a lens is adjusted by controlling a driving current of the VCM."

"Compared to traditional Voice Coil Motor (VCM) technology, which is constrained by weak magnetic fields and energy losses in small spaces, SMA actuators deliver at least 10 times the force in the same volume… This superior performance is driven by SMA’s stronger hold force and higher stiffness, which help keep the lens steady, even during rapid movements."

This small motor needs unipolar operation and max 110mA current. Resistance is 27 Ohm so max voltage is around 3V. The stroke of the motor changes when current between 25mA and 100mA. (From the discussion: position of the voice coil autofocus actuator directly depends on the current driven through the coil; to maintain a given displacement away from the spring’s rest position, a corresponding holding current must be supplied.)

A paper on a miniature standing wave linear ultrasonic motor states that such motors are attractive due to "small size, simple structure, and relative superior driving capability" for applications including "medical instruments, aerospace, optical devices, and precision positioning." While the abstract does not explicitly mention self-locking, standing-wave ultrasonic motors rely on frictional coupling that, as other sources explain, underpins their power-off holding capability.[8]

Voice Coil Motor (VCM) drivers are essential for camera autofocus in mobile phones, facilitating quicker and more accurate focusing. These drivers regulate the current through the autofocus voice coil to precisely control lens position, and must provide both dynamic drive current and holding current to keep the lens at the commanded focus position until the next change. The need for holding current contributes to the power consumption profile of VCM-based autofocus modules compared with alternative actuators that can hold position without power.

Piezoelectric autofocus motors (often implemented as ultrasonic or piezo drives) use the frictional coupling of a piezo-driven element against a guide to position the lens. When power is removed, the static friction between the lens carrier and guide typically holds the position without continuous electrical power, unlike many traditional VCM autofocus modules that rely on a restoring spring and therefore return to a mechanical rest position unless held by current or a specific self-locking mechanism.