'Artificial Joints' Inside Your Mobile Phone [Tech Talk]

Small OIS Built into Smartphones
Motor Moves Lens by Detecting Shake
Future Models Made with Shape Memory Alloy

When a person holds something with their hand, tiny hand tremors occur. The same applies when taking photos with a smartphone camera. However, the latest smartphone cameras can stabilize the focus no matter how severe the hand tremors are. This is thanks to image stabilization technology, which is now considered a standard feature in all smartphones.

Camera image stabilization is so commonly used in daily life that it hardly feels remarkable, but the technology involved in implementing this feature still represents the cutting edge of microengineering.

Lens Moving in the Opposite Direction of the Shaking Hand

The camera lens of a smartphone is the protruding part of the 'camera module'. [Image source=YouTube capture]

Smartphone cameras consist of a 'camera module.' This includes the basic components of a camera: the lens, the image sensor that converts light into digital data, and a device that automatically adjusts the camera’s image or compensates for hand tremors. The stabilization devices are broadly categorized into Optical Image Stabilization (OIS), Digital Image Stabilization (DIS), and Electronic Image Stabilization (EIS), with OIS being the most representative.

OIS is a type of electric motor called an 'actuator.' Originally, actuators are used in the joint parts of industrial robots powered by electricity. They move along four axes?up, down, left, and right?allowing the robot’s arms or legs to bend and stretch. Similarly, the OIS in a camera module corrects the image by continuously moving the lens whenever it detects tiny hand tremors. In other words, it is not an exaggeration to say that the smartphone we carry contains a small robotic joint inside.

Actual size of the camera module. It contains various components including the lens, image sensor, and actuator. [Image source=Phone Museum YouTube capture]

The smartphone camera module is a tiny machine about the size of a finger joint, and the OIS is even smaller. However, to ensure the precise operation of the actuator, various sensors are embedded inside the OIS. Representative components include a gyroscope sensor that detects tremors, a microcontroller unit (MCU) that analyzes the amount of shaking, and a driver IC that controls the motor in the opposite direction of the tremor. It also includes a Hall effect sensor and an interferometer to capture the exact amount of current flowing through the electric motor.

OIS exemplifies why smartphones are considered a 'culmination of modern technology.' It compresses a mechanical device that detects extremely minute positional changes and moves precisely in the opposite direction into the size of a finger joint. Moreover, this device is mass-produced at 700 million units annually (according to Counter Research reports) and installed in budget smartphones priced between 70,000 and 90,000 KRW. This progress is the result of collaboration among dozens or hundreds of companies worldwide, all aiming to enhance camera convenience.

Future Motors Made from 'Shape-Changing Metals'

In fact, a much more futuristic concept of OIS is expected to become widespread in the future. This is OIS using 'Shape Memory Alloy (SMA).' Shape memory alloys are metals that return to their original shape when heated to a specific temperature, typically made by combining nickel and titanium. They were researched in the 1960s in the United States for use in lunar exploration and are now being applied in various industries such as medical, mechanical, and automotive fields.

By weaving metal wires made from nickel-titanium shape memory alloy, it is possible to create a micro-mechanical device that moves in five directions (X, Y, Z axes). The force generated when heat is applied to this device, known as the 'returning force,' is used as the power source for the actuator. This actuator is called SMA OIS. Compared to conventional electric motor-based OIS, SMA OIS is much more energy-efficient and can finely control the force level to achieve movements on the micrometer scale.

Actuator made from Shape Memory Alloy (SMA) wire [Image source=Cambridge Mechatronics website]

Furthermore, because it does not require electric current, Hall sensors and current interferometers previously used in regular OIS can be omitted. This means it is possible to create an OIS much smaller than the already extremely tiny mechanical OIS. Reducing the space occupied by OIS within the camera module allows for more area for the image sensor and lens, which is also beneficial when manufacturing foldable smartphones that have more limited installation space than regular smartphones.

SMA OIS is known to have been first produced by a company called 'Cambridge Mechatronics' in collaboration with Foxconn. Although this technology was already realized in the 2010s, it was not adopted in general smartphones at the time due to its high cost.

However, recently, Chinese brands focusing on improving camera performance have increasingly adopted SMA OIS. The latest generation SMA-OIS has been installed in flagship phones from Huawei and HONOUR. As production volume increases and prices decrease, it is highly likely that SMA-OIS will be installed in mid-range and budget phones as well.

Smartphones are compact electronic devices the size of a palm that integrate almost all the functions needed for daily life. To realize this, technologies from numerous industrial fields, ranging from new materials to mechanical engineering, are generously applied. Since their first unveiling in 2007, smartphones have completely transformed human life and simultaneously accelerated human industrial capabilities.