Microelectromechanical Systems (MEMS) and Lab-on-a-Chip (LOC) technologies have integrated various functions on very small chips. Received physical and chemical signals are converted into electrical signals and biochemical reactions can be generated and processed on a chip. Beyond on-chip detections or responses, micromachines have the potential as intermediary tools for various interactions. A humanoid robot requires various sensors and actuators to mimic human functions. Specialized and differentiated industrial robots are equipped with sensors and actuators to accomplish their mission. Miniaturized microsensors are suitable for functionalizing robots without disturbing their basic functions. In addition, micromachines have potential as an intermediary tool for various interactions with a small world. Micro robots are capable of interacting with an environment in this small world, while humanoid robots are designed for human-robot interaction in a macro world. A combination of haptic interfaces with microrobots could even enable interaction between the small world and us.
Microsensors have been used to measure the force of small creatures such as insects. The flight power of flying insects, as a typical power of insects, has been measured by various means1,2,3,4,5,6. Direct measurement by microsensors and image processing for motion detection were used to measure force. The deformation, movement and generated force of a moth’s wings were measured optically using striped pattern projection1. The aerodynamic vertical force was about 7 mN. It is about 5 times stronger than the force of gravity acting on the moth (about 1.3 mN).
Drosophila flight forces were measured using a MEMS capacitive force sensor (3.6 mm × 2.1 mm × 0.5 mm) to understand the flight biomechanics of Drosophila (3 mm long)2. The capacitive sensor was developed using a silicon-on-insulator (SOI) substrate to capture instantaneous flight force in real time. Drosophila samples were bound to a sensor probe (3 mm x 50 μm x 50 μm). Total flight force has been estimated at a few tens of micronewtons. The collision avoidance behavior of the locust (40 mm body length) was studied using simultaneous force measurements and high-speed video recording. Interesting results have been reported on the relationship between flapping, lift and thrust3. The force and moment of take-off flight of fruit flies were analyzed using high-speed video techniques4. The contribution of jumping leg strength and flapping wing strength to fly lifting was studied. The vertical force of the talus (μN order) is sufficiently greater than the corresponding aerodynamic force. Social forces in the interaction of laboratory swarms of the flying midge Chironomus riparius were studied using multi-camera stereo imaging and particle tracking techniques to understand collective animal behavior5. The acceleration from each insect to its nearest neighbor was measured to estimate the repulsive and attractive forces in this study. The tensile strength of male Strepsiptera (Insecta) was measured to estimate the surface texture dependence of substrates6. The force was measured with a force sensor based on strain gauges attached to the insects by a thin polymer thread. The mean values of the force measured were less than 0.5 mN.
In addition to the flight force measurement, the leg forces of various insects were measured7,8,9,10. It has been reported that measuring the leg strength of a stick insect investigated the mechanism of control in the positioning of the joint in the legs7. On the path where stick insects walk, a platform with a force gauge has been prepared. The median of the difference between the force value at the beginning and end of the stimulus ramp was −3.0 mN (flexion) and 6.0 mN (extension). A multi-axis piezoresistive sensor with micronewton force resolution has been reported to measure the foot force of insects smaller than cockroaches, such as ants8. The sensor shown had a minimum force resolution of the order of 0.5 mN. Plant-insect interactions on leaflets have been studied by measuring the adhesive (pulling) forces generated by beetles on different plant substrates9. The dorsal surface of the beetle’s thorax was attached to a load cell force sensor with hair. The measured maximum tensile forces on plant surfaces differed from the force generated on glass as a control ranging from 0.5 to 11.8 mN. A number of micro force plates using strain gauges to measure the ground reaction forces of insect legs have been reported10. The force resolution was 1 μN.
Not only animals but also plants generate forces to deform their shape and change their physical properties. The movement of the top leaf of the Venus flytrap is an example of a well-known movement produced by a plant. Measurement of the forces generated by the Venus flytrap hitting, holding and squeezing the prey has been reported11. A piezoelectric sensor was used to directly measure the mean impact force of the trap along with a video camera to determine time constants. For example, the average impact force between the edges of two lobes in the Venus flytrap was found to be 149 mN.
Most previous work has focused on measuring insect behavior such as flight forces and leg forces. This paper presents for the first time microrobot-insect interactions through a soft microfinger integrated with an artificial muscle actuator and a tactile strain sensor, as shown in Fig. 1a. A micro finger can exert force on an objective insect and stimulate the insect. The micro finger artificial muscle actuator, which is a polymer pneumatic balloon actuator (PBA), is soft and safe enough to gently interact with insects12,13. Microfinger manipulation robotic systems have been developed using PBA for object grasping motions12. A tiny fish roe has been successfully manipulated. In addition, microfingers have been developed for the manipulation of cell aggregates13. A spherical aggregate of human mesenchymal stem cells (hMSC) (φ200 μm) was crushed and released onto a microtiter plate. In addition to artificial muscle micro-actuators, our study includes the integration of tactile sensors in a micro-finger. A flexible temperature sensor was integrated into a microfinger to record the temperature14. Several types of strain sensors have been studied for motion detection of a microfinger. Recently, a strain sensor using a liquid metal (Galinstan) filled microchannel was developed for PBA15,16,17. The liquid metal strain gauge is a resistive type and its k-factor is reported to be around 115. The strain sensor can be made by filling liquid metal into microchannels. This study uses the common channel structures for both the sensor and the pneumatic balloon actuator. This study shows that the liquid metal strain sensor integrated into the microfinger can detect the reaction force of an insect. Therefore, the microfinger enables active force measurement against living insects. Previously, a bilateral mechanical scaling tool was developed by Mohand Ousaid et al.18 and applied to interactions between an insect. The instrument system consisted of an active probe and hand interfaces for bilateral interaction. They used an insect leg to study water droplets. We have also developed and reported a haptic teleoperation robotic system consisting of a slave microfinger and a master interface device for an operator19,20. This article introduces a microfinger as a microscopic end effector for the active perception of an insect’s reaction force, which in combination with the interaction system, such as a bilateral control system18 and a haptic, has the potential of microfinger-insect interactions in the small world teleoperation system19,20.
illustration 1
Microfinger-insect interaction. (a) Schematic representation of the interaction between microfinger and insect (pill bug). Shade3D Basic ver. 17.0.0 (https://shade3d.jp/en/) was used to create the images. (b) Photo of a developed micro hand with five micro fingers. This study focuses on a single micro-finger, while the micro-hand in the photo (b) implies the potential of human hand-insect interactions through the robotic haptic teleoperation system19,20.
