Akifumi Takahashi

Smartwatches gained popularity in the mainstream, making them into today’s de-facto wearables. Despite advancements in sensing, haptics on smartwatches is still restricted to tactile feedback (e.g., vibration). Most smartwatch-sized actuators cannot render strong force-feedback. Simultaneously, electrical muscle stimulation (EMS) promises compact force-feedback but, to actuate fingers requires users to wear many electrodes on their forearms. While forearm electrodes provide good accuracy, they detract EMS from being a practical force-feedback interface. To address this, we propose moving the electrodes to the wrist—conveniently packing them in the backside of a smartwatch. In our first study, we found that by cross-sectionally stimulating the wrist in 1,728 trials, we can actuate thumb extension, index extension & flexion, middle flexion, pinky flexion, and wrist flexion. Following, we engineered a compact EMS that integrates directly into a smartwatch’s wristband (with a custom stimulator, electrodes, demultiplexers, and communication). In our second study, we found that participants could calibrate our device by themselves Math 1 faster than with conventional EMS. Furthermore, all participants preferred the experience of this device, especially for its social acceptability & practicality. We believe that our approach opens new applications for smartwatch-based interactions, such as haptic assistance during everyday tasks.

Electrical muscle stimulation (EMS) became a popular method for force-feedback without mechanical-actuators. While much has been written about the advantages of EMS, not much work has investigated circumventing its key limitations: (1) as impulses traverse the skin, they cause an uncomfortable “tingling”; (2) impulses are delivered via gelled-electrodes, which not only require direct skin contact (must be worn under clothes); but, also (3) dry up after a few hours. To tackle these, we explore switching from electrical to magnetic muscle stimulation (MMS), via electromagnetic fields generated by coils. The first advantage is that MMS coils do not require direct skin contact and can actuate up to 5 cm away (Study#1)—this enables applications not possible with EMS, such as stimulation over the clothes and without ever replacing electrodes. Second, and more important, MMS results in ∼50 % less discomfort caused by tingling than EMS (Study#2). We found that reducing this tingling discomfort has two downstream effects for interactive systems: (1) participants rated MMS force-feedback as more realistic than that of EMS (Study#3); and (2) participants could more accurately perceive the pose actuated by the interactive system (Study#4). Finally, we demonstrated applications where our proposed switch from EMS to MMS improves user experience, including for VR feedback, gaming, and pose-control.

When an object that is grasped with a finger is pulled by an external force, the traction force is perceived by cutaneous receptors and proprioception in the finger. Several attempts have been made to simulate the pulling sensation by using wearable devices, including mechanical asymmetric vibration and tightening by belt. In this study, we developed a new method that uses electrical simulation to generate an illusory force sensation by simulating the activity pattern of the cutaneous receptors. We validated our method through two experiments, one based on force direction judgment and the other on force magnitude adjustment.

Many wearable interfaces have been proposed to present force to the upper limb and elbow joint. One way to achieve a compact wearable haptic interface is to use electrical stimulation, and we have suggested that transcutaneous electrical stimulation above the wrist tendon can produce force a sensation in the direction of the muscle stretching; however, it has not been investigated in detail whether the force sensation presented by the electrical stimulation of the tendon occurs in the upper limb joints. In this study, to investigate whether the force sensation is generated when applying electrical stimulation of the skin at the tendon or at the muscle belly of the biceps brachii muscle, we quantitatively evaluated the direction and amount of the force sensation under the aforementioned conditions. The results showed that the electrical stimulation of the tendon produced significant force sensation in the direction of elbow extension. On the other hand, in some participants, the electrical stimulation of the muscle belly worked as a supporting force, resulting in the sensation of weakened force perception. In general, we concluded that the sensation produced by muscle stimulation was different from that produced by stimulation of the tendon.

We demonstrate a technique that allows an unprecedented level of dexterity in electrical muscle stimulation (EMS), i.e., it allows interactive EMS-based devices to flex the user's fingers independently of each other. EMS is a promising technique for force feedback because of its small form factor when compared to mechanical actuators. However, the current EMS approach to flexing the user's fingers (i.e., attaching electrodes to the base of the forearm, where finger muscles anchor) cannot flex one finger alone at the metacarpophalangeal (MCP) joint, they always induce unwanted actuation to adjacent fingers. To tackle the lack of dexterity, we propose a new electrode layout that places the electrodes on the back of the hand, where they stimulate the interossei/lumbricals muscles in the palm, which have never received attention with regards to EMS. We demonstrate the improved dexterity with a series of EMS-assisted music applications for playing piano, drums, and guitar.

Figure 1: Left: positions of vibrators and trackers

The quantification of stickiness experienced upon touching a sticky or adhesive substance has attracted intense research attention, particularly for application to haptics, virtual reality, and human–computer interactions. Here, we develop and evaluate a device that quantifies the feeling of stickiness experienced upon touching an adhesive substance. Keeping in mind that a typical pressure distribution sensor can only measure a pressing force, but not a tensile force, in our setup, we apply an offset pressure to a pressure distribution sensor and measure the tensile force generated by an adhesive substance as the difference from the offset pressure. We propose a method of using a magnetic force to generate the offset pressure and develop a measuring device using a magnet that attracts magnetic pin arrays and pin magnets; the feasibility of the method is verified with a first prototype. We develop a second prototype that overcomes the noise problems of the first, arising from the misalignment of the pins owing to the bending of the magnetic force lines at the sensor edges. We also obtain measurement results for actual samples and standard viscosity liquids. Our findings indicate the feasibility of our setup as a suitable device for measuring stickiness.