Cinematic video quality is increasingly marketed with the latest smartphone cameras. This means that consumers are now looking for video mode capabilities with an increasing array of use cases, such as walking, running and cycling. To provide the best possible video mode output, optical image stabilisation (OIS) is required to avoid user generated picture blur.
Rotation out of the sensor plane is the dominant source of image blur for most imaging conditions, for which tilt motion compensation provides the ideal optical solution. However, the majority of image stabilisation is achieved by moving the lens with respect to the image sensor, known as Lens Shift OIS. With Sensor Shift OIS, it is the image sensor which moves with respect to the lens barrel. For both Lens Shift and Sensor Shift an angular correction is enabled by shifting the lens or sensor in a translation movement parallel to the sensor plane. Whilst this can result in images or videos showing good suppression at the centre, Lens Shift and Sensor Shift solution may still show motion blur in the corners. Corrections using computation software are often used, but these result in a reduction of the video resolution and thus the overall quality.
Module Tilt moves a standalone camera module, with the lens and image sensor fixed in position with respect to each other. The result is superior image quality as uniform image stabilisation across the entire image sensor is achieved.
Lens Shift and Sensor Shift OIS cameras are typically rated to ±1.5deg shake compensation. Above that, the image quality visibly degrades. For Module Tilt, a uniform shake correction can be achieved for higher shake amplitude, currently up to ±3deg. The mechanical OIS means there is no need for an EIS application that reduces the output image resolution from the image sensor. These capabilities allow Module Tilt OIS to extend the video use cases from hand shaking correction to action camera applications.
The main challenges with Module Tilt OIS are moving a standalone camera module with image sensor whilst simultaneously connecting it to the handset and maintaining a small footprint and thinness. The interconnect must transmit electrical current and data whilst in motion when the camera OIS is in use and must do so reliably over many years of use. The actuator needs to be able to control the position of the image sensor very fast and accurately, overcoming all resistive forces from the interconnect.
A traditional voice coil motor (VCM) actuator using magnets and electromagnetic coils relies on a gimbal construction to hold an Autofocus (AF) camera module in place, limiting the motion to X and Y tilt only. The necessity of a gimbal structure also increases the camera module height. Furthermore, because of the inherent limitations in force the VCM design can generate, it relies on a long flexible printed circuit (FPC) with multiple 180 degree folds, adding significantly to the camera footprint. These design, performance and cost compromises made in the currently available VCM solution have limited its wider industry adoption.
Cambridge Mechatronics (CML) have developed a Module Tilt OIS actuator system using Shape Memory Alloy (SMA) technology, SMA wires of 30um diameter are configured to hold the AF camera module in a cradle position. These SMA wires contract and expand upon heating and cooling with high force to move the camera module in a tilt and roll motion to a desired position. Fast and precise control of the actuator and camera is delivered by CML's unique IC and Firmware to generate ultimate OIS performance. CML's use of SMA technology enables a design approach that allows CML's Module Tilt system to overcome the drawbacks of a VCM system.
CML’s 1/1.56” Module Tilt prototype actuator and camera module data packs and evaluation kits are now available for performance testing and demonstrations.
Module Tilt OIS is very well suited for adoption in the next generation of smartphone cameras looking to increase video mode quality and expands use cases from astrophotography to active modes such as running and cycling. CML and its use of SMA technology provides cutting edge solutions to its customers that are miniature and more flexible in design than VCM solutions with a roadmap that ensures new features and uses cases are enabled in the next 3 years.
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