A simplified model of a multi-jointed mechanical finger calibrated with experimental data by vision system

The development of suitable models for mechanical fingers, whether they are part of prosthetic device or of a robotic hand, is a powerful tool to predict the behaviour of their components since the early stages of design, especially for underactuated mechanisms. Experimental data can improve the reliability of such models and promote their application to build proper control strategies especially for prosthetic hands. Here, we have developed a multi-jointed model of a mechanical finger. The finger is part of the Federica hand: an underactuated mechanical hand that was conceived for prosthetic purpose. The model accounts for friction phenomena in the finger and it is tuned with experimental data acquired through a digital image correlation device. The model allowed us to write kinematics relations of the phalanges and evaluate finger configurations in relation to the closure velocity. Moreover, it was possible to estimate the tendon force and the work analysis occurring during the closure tasks, both in free mode and in presence of objects.

Soft curvature sensors for measuring the rotational angles of mechanical fingers

The design, fabrication, and testing of soft sensors that measure elastomer curvature and mechanical finger bending are described in this study. The base of the soft sensors is polydimethylsiloxane (PDMS), which is a translucent elastomer. The main body of the soft sensors consists of three layers of silicone rubber plate, and the sensing element is a microchannel filled with galliumindium-tin (Ga-In-Sn) alloy, which is embedded in the elastomer. First, the working principle of soft sensors is investigated, and their structure is designed. Second, the relationship between curvature and resistance is determined. Third, several sensors with different specifications are built in accordance with the structural design. Experiments show that the sensors exhibit high accuracy when the curvature changes within a certain range. Lastly, the soft sensors are applied to the measurement of mechanical finger bending. Experiments show that soft curvature sensors can effectively reflect mechanical finger bending and can be used to measure the bending of mechanical fingers with high sensitivity within a certain working range.

Evaluation of the Possibility of Shaking Off Raspberry Fruits with a Pulsating Air Stream

The aim of the study was to determine the possibility of harvesting raspberries with a pulsating air stream that causes the shoots of plants to vibrate. Two tractor-driven test devices were developed under this specific objective. The first one was a high capacity compressor, and the stream of air produced by it was directed onto one side of a row of plants. The second one was a device producing two counter-flowing air streams colliding in the middle of a row of plants. The frequency of the air pulses was adjusted steplessly by varying the rotational velocity of the shutters closing and opening the outlets of the fans. In the field trials with the device based on a compressor-generated air stream, two air pulse frequencies were used: 500 and 540 pulses per minute (8.3 and 9 Hz). The mean detachment force was 0.727 N. About 50% of ripe raspberries were removed from the bushes. The results achieved during harvesting with the device operating on the principle of colliding two pulsating air streams were markedly better and put the harvesting effectiveness within the range achieved in the trials with combine harvesters with mechanical finger shakers conducted by other researchers. For two pulse frequencies (8 and 9 Hz), almost 62% of fruits were harvested. Increasing the pulse frequency of the counter-flowing air streams above 9 Hz did not improve the effectiveness of detaching raspberry fruits from shoots.

Study of an Underactuated Mechanical Finger Driven by Tendons

This paper presents an investigation on the influence of the design parameters in an underactuated mechanical finger driven by un-extendable tendons. The study was carried out using simulations and experimental tests. The aim of the study is to analyze the behavior of the finger during its closing motion. Hence, this study can help in correctly designing fingers for underactuated grasping devices. Various design aspects and parameters were taken into account to optimize the dynamic behavior of the mechanism in the simulation. The actions of the tendons were modelled with the forces that the tendon exerts on the phalanges.

Autonomous Pedestrian Push Button Activation by Outdoor Mobile Robot in Outdoor Environments

The authors have developed an outdoor mobile robot that has the ability to cross roads at an intersection or pedestrian crossing fully autonomously while traveling along sidewalks in an urban environment. This gives the robot the capability to travel longer and complex routes as the robot is able to cross a road and continue with its path. The developed robot has the unique ability to autonomously approach and activate the pedestrian push button with a mechanical finger. We first briefly describe the overall operation of such a road crossing robot. The rest of this paper then discusses in detail how the robot can meticulously navigate to and activate the pedestrian push button with the on-board finger. The contribution of this work is that although there are robots existing that perform precision docking or button activation, this robot is one of the few that can perform such an action in a real world outdoor environment that is completely unmodified. We prove this by deploying the robot in a real world road-crossing and it was successfully able to engage the pedestrian push button.