Unveiling the hero behind the smart lift design: Smart Linear Actuator

Image source: Who is Danny/Shutterstock

Linear actuators convert the inherent rotational motion of a motor rotor into linear motion for loads of all sizes. It consists of a motor, linear guides, and drive control electronics, and may also include wired/wireless connectivity and control schemes. Although linear actuators have a low presence to the user, they are standard components used in a wide range of fields such as automotive, aerospace, agriculture, manufacturing, solar energy, medical, and robotics ( Figure 1 ), and are increasingly entering home and consumer products, serving a variety of home functions that you can see or cannot see. It can simplify some originally complex tasks while also providing new options for interior design.

Depending on the needs of the specific application, the power supply of the linear actuator can come directly from the AC line or use a small AC/DC converter. It changes the position of the load by extending and retracting, such as lifting or lowering objects, opening and closing lids, etc. Its applications in consumer scenarios include blinds and curtains, retractable awnings ( Figure 2 ), lift-type TV stands ( Figure 3 ), recliners, adjustable beds, skylights, lift-type integrated stoves, and duct dampers.

Figure 2: Linear actuators are ideal for opening and retracting outdoor awnings (Image credit: Studio Harmony/Shutterstock)

However, with the development of technology, linear actuators are no longer limited to industrial scenarios. Today, small high-power motors have become more mature, and both motors and actuators can be managed by high-performance control electronics. In addition, wired or wireless interfaces can be easily added through infrared control (similar to a TV remote control), Bluetooth connection, Wi-Fi link, or proprietary wireless link for remote control. In addition, today's homes are full of AC outlets, which can more easily meet the low duty cycle/high peak power requirements of smart linear actuators, and no batteries are required, which also saves the homeowner a lot of trouble.

Factors driving smart linear actuators include:

There are many ways to achieve this conversion. One economical and efficient way is to connect a lead screw (a long threaded rod) to the motor shaft, screw a nut (a cylindrical object with female threads) on it (Figure 4), and then connect the load to be moved to the nut. In this way, the rotation of the motor shaft will drive the lead screw to rotate, so that the nut drives the load to move along the lead screw.

Figure 4: The principle of using a lead screw to achieve linear motion is modified from a bolt and nut. The motor drives the lead screw to rotate, and the nut on it drives the load to move (Source: Design and Technology Resources)

A less expensive alternative to using a lead screw is to mount a toothed pulley, usually made of plastic, on the motor shaft and mesh it with a flexible, non-retractable belt with a matching tooth profile ( Figure 5 ). The load is secured to the belt and the far end of the belt is meshed with another, unpowered idler pulley to maintain proper tension. This pulley-and-belt approach is ideal for long linear motions, such as pulling a curtain across a window.

Figure 5: In some cases, a toothed belt and matching pulleys can be used to convert rotary motion into linear motion.

(Image source: Teknic, Inc.)

The STSPIN32F0 advanced BLDC controller from STMicroelectronics is an example of such a controller. This is a controller for brushless DC motors with an embedded microcontroller unit (MCU) ( Figure 6 ). This IC combines basic power management, an ARM processor core, memory, sensor analog inputs, motor MOSFET drivers, a range of serial interfaces, etc. Users can develop their own motion control algorithms to suit their applications, or customize them based on pre-provided algorithm packages.

From the many products of Trinamic Motion Control (acquired by Analog Devices in August 2021), it can be seen that intelligent motor controllers can realize a variety of motion trajectory curves, including basic trapezoidal curves ( Figure 7 ) and more complex curves such as S-curves ( Figure 8 ). The S-curve has a smooth change in speed and/or acceleration when the motion starts and stops. Compared with the trapezoidal curve, the S-curve has less impact on loads such as curtain rods and lift-type TV stands, and is more acceptable to consumers.

Figure 7: The trapezoidal acceleration curve is the easiest to implement and is a common solution (Source: Trinamic GMBH)

Figure 8: Smart motion controllers can achieve S-shaped speed curves, reduce potentially harmful sudden starts and stops, improve long-term reliability, and make it easier for consumers to accept (Source: Trinamic GMBH)

The types of feedback control sensors available are Hall effect devices, resolvers, optical encoders, and simple potentiometers. Hall effect devices have the lowest resolution, but they are also the lowest cost and easiest to integrate into a mechanical design. Since consumer products generally do not require very high accuracy, Hall effect devices are more than adequate. Resolvers and optical encoders are very expensive and very difficult to integrate. Potentiometers are not expensive, but they may degrade over time and their reliability is dependent on the environment; however, these disadvantages may not be a problem for consumer products because such products are not used frequently and the physical environment they are in is usually relatively mild.

Further reading: Options other than motors Among the drive methods of linear actuators, the design of pneumatic and hydraulic pistons has a history of more than 100 years of use ( Figure 9 ). The technology is mature and works well, with good performance in many aspects (force, size, speed, accuracy, etc.).

However, they are generally not suitable for consumer applications, and their disadvantages are more obvious when compared with electric motor solutions, which are easier to install and control and only require a basic power connection to operate, without the need for air or hydraulic oil compressors and interconnecting pipes, and the compressor's own motor also requires electricity. In addition, hydraulic oil may leak, while electric motors do not have such problems and do not risk harming the environment in the event of failure.

With smart linear actuators driven by efficient motors, linear electromechanical devices are entering the home consumer space. Smart linear actuators combine new technologies in motion controllers, motors, mechanical drive components, and wired/wireless connectivity to provide designers with an easy-to-use and cost-effective way to solve linear motion control problems in existing and new applications.