Hikaru Sasaki

An active tactile sensor for detecting mechanical characteristics of contacted objects

We propose an active tactile sensor actuated by magnetic force. The tactile sensor has the advantage of being able to detect mechanical characteristics related to a tactile impression of contacted objects using a single sensor structure, much as human skin functions. It consists of a displacement-sensing element of piezoresistors formed on a silicon diaphragm, and a magnetic actuating element (a permanent magnet and a flat coil). The sensor has two modes of operation, quasi-static and vibration, and it can detect contact force, elasticity and damping of contacted objects by choosing between operation modes. We fabricated the piezoresistor sensing and magnetic actuating elements by applying the microelectromechanical systems technologies, and assembled them in a hybrid manner. The size of the sensor was 6.0 mm × 6.0 mm × 10 µm. As contact samples we used three different rubber materials with hardness values ranging from A20 to A60 in Shore A. We experimentally confirmed that both the resonance frequency and the Q-factor of the sensing element in the vibration mode changed with different samples. We were able to calculate the elastic and damping coefficients of the contacted rubber objects by analyzing the vibrational response of the diaphragm. From the results, we concluded that the active sensor can detect mechanical characteristics of contacted objects using a single sensor structure.

A Novel Type of Mechanical Power Transmission Array for Switching Densely – Arrayed Actuator Systems

This paper proposes a novel type mechanical transmission system for driving arrayed elements. The main advantage of this system is that it is able to operate individually arrayed elements with high-power. It was fabricated by MEMS technologies, and was confirmed that we are able to individually drive the arrayed elements by selectively driving tulip-shaped electrostatic clutch devices that transmit large power coming from a single power source. The transmitted stroke was 20 µ m for this experiment.

Multifunctional active tactile sensor using magnetic micro actuator

This paper proposes a multifunctional tactile sensor device driven by magnetic force. The device has the advantage that it can detect multiple physical values, such as contact-force and the elastic and damping coefficients of a contacted object. We previously used an external pneumatic system for actuating the device, and confirmed it can measure the elastic-coefficient of an object. This time, we realized hybrid active tactile sensor system by assembling a magnetic driving mechanism for detecting multiple physical values. We also developed a theoretical model of the detection, and experimentally confirmed both elastic and damping coefficient detection by using different types of silicone rubbers as samples.

Magnetic actuation of a micro-diaphragm structure for an active tactile sensor

We previously proposed an active tactile sensor that detects both the contact force and hardness of objects such as fingertips. We validated the device principle by using a pneumatic actuation system [1-2]. As a new method for driving the sensor element, we proposed the idea of using a magnetic force working between a permanent magnet on the sensor element and a microfabricated flat coil. We developed the flat coil by using thick photoresist as a mold and electroplated copper as a conductor. We assembled the sensor element and the flat coil, and constructed a hybrid active tactile sensor system. When we dynamically drove the sensor with the magnetic actuator, we could drive the sensor element around its mechanical resonance frequency. We expect that this active tactile sensor can detect a variety of information about an object, such as its hardness and damping factor.

A force transmission system based on a tulip-shaped electrostatic clutch for haptic display devices

This paper describes a novel type of force transmission system for haptic display devices. The system consists of an array of end-effecter elements, a force/displacement transmitter and a single actuator producing a large force/displacement. It has tulip-shaped electrostatic clutch devices to distribute the force/displacement from the actuator among the individual end effecters. The specifications of three components were determined to stimulate touched human fingers. The components were fabricated by using micro-electromechanical systems and conventional machining technologies, and finally they were assembled by hand. The performance of the assembled transmission system was experimentally examined and it was confirmed that each projection in the arrayed end effecters could be moved individually. The actuator in a system whose total size was only 3.0 cm × 3.0 cm × 4.0 cm produced a 600 mN force and displaced individual array elements by 18 µm.

Selective removal of micro-corrugation by anisotropic wet etching

We conducted an investigation to find a corrugation removal mechanism selectively by anisotropic wet etching to reduce a periodic corrugation, called “scalloping”, formed on the sidewalls of microstructures by Deep Reactive Ion Etching (D-RIE). We analyzed the corrugation removal mechanism by using an etching distribution pattern, and then conducted several equations to predict the corrugation removal time by the etching. We experimentally tried to perform a selective removal of the corrugation by using 50% KOH (40 deg-C). The corrugation formed on Si{100} sidewall surfaces gradually reduced in size with the advance of the etching, and it was completely removed after5.0 min of etching. The necessary etching time and shape change of the corrugation removal were coincident with the results conducted by the distribution pattern of the etching.

Electrostatic Latch Mechanism for Handling Projection on Arrayed Vertical Motion System

We have previously proposed an arrayed vertical motion system based on a tulip-shaped electrostatic clutch for producing haptic displays. The system has an advantage in that it is able to individually operate arrayed end-effecter elements with high-power and large strokes (output: 600 mN and displacement: 60 mum). We added a new electrostatic latch mechanism to the system to individually control the projection state. We used MEMS technologies to fabricate a 4times4 array electrostatic latch mechanism. The total size of the mechanism was 6.0 times 6.0 times 0.5 mm. We evaluated the relationship between the applied voltage and a holding force of a few mN was obtained for the spring device.

Integration of Skeletal Muscle Cell onto Si-MEMS and its Generative Force Measurement

We propose skeletal muscle cells as a new material for Bio-MEMS actuator, and developed the fabrication process to integrate it onto Si-MEMS devices. As the first trial of the integration of the skeletal muscle cells onto the Si-MEMS device, we used a cantilever-based force measurement Si-MEMS device for evaluating the generative force of the muscle cells. Murine skeletal muscle cell line C2C12 myoblasts were patterned on the device by using poly-N-isopropylacrylamide as a sacrificed layer. The cell-patterned device was immersed into the cell culture medium and cultivated for 7 days. The results of the immunological staining of the muscle specific protein, ¿-actinin, confirmed that the patterned myoblasts successfully differentitated into myotubes on the device. Then, we applied the electrical stimulation to the myotubes, evaluated the active tension generated from the myotubes, and revealed that its tetanic value was approximately 1.2 ¿N.

Projection Clutching System for Force Transmission System based on Tulip-shaped Electrostatic Clutch

We have previously proposed an arrayed vertical motion system based on a tulip-shaped electrostatic clutch for producing haptic displays. The system has an advantage in that it is able to individually operate arrayed minute projection with high-power and large strokes (Output: 600 mN and displacement: 60 mum). This time, we added a new electrostatic latch mechanism to the system to individually control the projection state. We used MEMS technologies to fabricate a 4x4 array electrostatic latch mechanism. The total size of the mechanism was 6.0 x 6.0 x 0.5 mm. We evaluated the relationship between the applied voltage and a holding force of a few mN was obtained for the spring device.

A New Explanation of Mask-corner Undercut in Anisotropic Silicon Etching: Saddle Point in Etching Rate Diagram

We investigated undercut phenomena on a (100) silicon wafer to explain why a (311) plane appears under the convex corner of a masking area, and why the plane is stable during the etching process. We analyzed the etching rate as a function of crystallographic orientations and found that the (311) plane has unique etching characteristics. The (311) plane is located at the saddle point in the etching-rate diagram. Based on this, we made an undercut model, which provides clear answers to the above questions. We demonstrated that our model can also explain the etched-profile change in terms of the change in the mask shape when a windmill-shaped etching mask is used.