Developing New Sensor Devices Utilizing Piezoelectric Property of Polylactic Acid

Proposing Application Devices Capitalizing on Characteristics

Leaf Grip Remote Controller

The Leaf Grip Remote Controller (Fig. 4) controls a TV through simple bending and twisting motions. There are two acrylic plates layered in its central area, one affixed with a bend-sensing piezoelectric film and the other affixed with a twist-sensing piezoelectric film. A flexible photovoltaic power generation device (dye-sensitized photocell) is inserted between two plates (Fig. 5) .

The power-generating efficiency of the photocell is unaffected because of the high transparency of piezoelectric films. Rechargeable batteries, power-supply circuits, transmission circuits and sensor circuits are built into grips on both ends. A photocell generates power whenever exposed to light and power is stored in rechargeable batteries, eliminating the need for exchanging of batteries.

This remote controller can control a TV with the following actions.

  • Lightly shaking: Turning the power ON or OFF
  • Twisting: Switching channels
  • Bending: Adjusting the volume
  • Quickly twisting twice: Switching the input source

This remote controller is an experience a world apart from conventional remote controllers with its intuitive operations without having to look for buttons. For example, a senior user would be freed from putting on a pair of reading glasses just to find correct buttons to push.

Fig. 4 External view of the Leaf Grip Remote Controller

Fig. 4 External view of the Leaf Grip Remote Controller

Fig. 5 Cross-sectional view of the Leaf Grip Remote Controller

Fig. 5 Cross-sectional view of the Leaf Grip Remote Controller

Touch Pressure Pad

Touch pressure pad (Fig. 6) realizes XYZ 3-axis sensing by adding pressing force sensing to a conventional capacitance type touch-panel. An electrode to detect voltage generation from the pressure was composited to the conventional capacitance type position-sensing electrode on both sides of the bend-sensing piezoelectric film. Slight warp in the touch panel from pressure can now be sensed (Fig. 7) .

With PDVF, it was unable to sense the pressure exactly, since its pyroelectric property caused voltage generation from the temperature of the fingertip. Absence of pyroelectricity in PLLA, on the other hand, allows for exact pressure sensing. Pressure sensing is realized not by adding other sensors such as a distortion sensor to the conventional touch panel, but rather the touch panel itself can detect the pressure, therefore making its construction very simple. Another advantage of PLLA is its excellent light transmittance when implemented to a touch panel having transparent electrodes.

Fig. 6 External view of a touch pressure pad

Fig. 6 External view of a touch pressure pad

Fig. 7 Sensing principle of a touch pressure pad

Fig. 7 Sensing principle of a touch pressure pad

Final Remarks

Displacement sensors, triggering voltage fluctuation from a bend or twist displacement, may be implemented to intuitively controlled operations of game machines and care equipment. It is also applicable for kinetically controlling (Fig. 8) futuristic mobile phones. The touch pressure pad technology, implemented to the touch panel itself, can help detect bend and twist actions. This touch panel, equipped with conventional gesture recognition in addition to bend and twist, is capable of more advanced intuitive HMI. Sensors used in equipment controlled by hand must be made with non-pyroelectric material such as PLLA to prevent temperature-related detection errors. We intend to continue developing sensor products that can bridge between people and machines in all kinds of situations.

Glossary

*1 Biodegradable Polymer: Biodegradable polymers are decomposable by microorganisms. Although PLLA may be completely broken down into water and carbon dioxide by hydrolytic bacteria in the soil, it is quite stable while exposed to air.
*2 Pyroelectricity: Pyroelectricity is a phenomenon where polarization of a dielectric material (surface charge) changes from a change in temperature.
*3 Chirality: Chirality is a characteristic where a three-dimensional figure, object or phenomenon cannot be superimposed by their mirror images.

Application Note