Prototype End-effector Research Articles

A rapid-response soft end effector inspired by the hummingbird beak.

Biology is a wellspring of inspiration in engineering design. This paper delves into the application of elastic instabilities-commonly used in biological systems to facilitate swift movement-as a power-amplification mechanism for soft robots. Specifically, inspired by the nonlinear mechanics of the hummingbird beak-and shedding further light on it-we design, build and test a novel, rapid-response, soft end effector. The hummingbird beak embodies the capacity for swift movement, achieving closure in less than [Formula: see text]. Previous work demonstrated that rapid movement is achieved through snap-through deformations, induced by muscular actuation of the beak's root. Using nonlinear finite element simulations coupled with continuation algorithms, we unveil a representative portion of the equilibrium manifold of the beak-inspired structure. The exploration involves the application of a sequence of rotations as exerted by the hummingbird muscles. Specific emphasis is placed on pinpointing and tailoring the position along the manifold of the saddle-node bifurcation at which the onset of elastic instability triggers dynamic snap-through. We show the critical importance of the intermediate rotation input in the sequence, as it results in the accumulation of elastic energy that is then explosively released as kinetic energy upon snap-through. Informed by our numerical studies, we conduct experimental testing on a prototype end effector fabricated using a compliant material (thermoplastic polyurethane). The experimental results support the trends observed in the numerical simulations and demonstrate the effectiveness of the bio-inspired design. Specifically, we measure the energy transferred by the soft end effector to a pendulum, varying the input levels in the sequence of prescribed rotations. Additionally, we demonstrate a potential robotic application in scenarios demanding explosive action. From a mechanics perspective, our work sheds light on how pre-stress fields can enable swift movement in soft robotic systems with the potential to facilitate high input-to-output energy efficiency.

Autonomous Installation of Electrical Spacers on Power Lines Using Magnetic Localization and Special End Effector

The combined effects of environmental factors such as high winds and melting ice can cause transmission line conductors to vibrate at high amplitudes, resulting in damaged pole structures, cracked insulating strands, and short circuits. The manual installation of electrical spacers between the two power line conductors is currently the only way to prevent this, but due to the high-voltage environment, this operation is extremely dangerous for a human worker. As a solution to automate this operation, the autonomous installation of electrical spacers using a robotic manipulator is proposed. For this purpose, a design of a special end effector for the robotic installation of electrical spacers is proposed. The end effector prototype was produced and tested under laboratory conditions and then used for the autonomous installation of spacers on power lines. Its localization with respect to the power lines is based on measurements of the magnetic field generated by the alternating currents flowing through the power lines. To verify the feasibility of the proposed solution under laboratory conditions, the proposed end effector equipped with magnetometers was developed and mounted on a 6-axis Schunk LWA 4p robotic arm. The implemented autonomous installation sequence was successfully verified using a robot and a laboratory mock-up of power lines.

갈고리를 사용한 줄기 절단으로 과채에 남겨진 줄기 길이를 최소화하는 수확용 엔드이펙터

This paper proposes a harvesting end-effector to minimize the length of the rested stem remaining on the fruit by stem-cutting with a hook. The proposed end-effector draws the stem of the target fruit to the cutter with a hook mechanism and decreases the length of the rested stem that can cause damage to other fruits in the process of packaging and transportation. The hook mechanism is composed of two links and a cam moves the hook tip in an arc with one motor to hang the stem. When designing the end-effector prototype, it was sized by considering the range of hook motion and the condition of the harvest. The prototype of the end-effector was fabricated by 3-D printing and its performance was measured by a harvesting experiment using a tomato model and a real stem. In the experiment, the success rate of the harvest and the minimization of the rested stem were measured. Finally, it was verified that the proposed end-effector could increase crop yield and efficiency of the harvest by harvesting the fruit successfully and minimizing the rested stem after harvest.

A five-bar mechanism to assist finger flexion-extension movement: system implementation

AbstractThe lack of specialized personnel and assistive technology to assist in rehabilitation therapies is one of the challenges facing the health sector today, and it is projected to increase. For researchers and engineers, it represents an opportunity to innovate and develop devices that improve and optimize rehabilitation services for the benefit of society. Among the different types of injuries, hand injuries occur most frequently. These injuries require a rehabilitation process in order for the hand to regain its functionality. This article presents the fabrication and instrumentation of an end-effector prototype, based on a five-bar configuration, for finger rehabilitation that executes a natural flexion-extension movement. The dimensions were obtained through the gradient method optimization and evaluated through Matlab. Experimental tests were carried out to demonstrate the prototype’s functionality and the effectiveness of a five-bar mechanism acting in a vertical plane, where gravity influences the mechanism’s performance. Position control using fifth-order polynomials with via points was implemented in the joint space. The design of the end-effector was also evaluated by performing a theoretical comparison, calculated as a function of a real flexion-extension trajectory of the fingers and the angle of rotation obtained through an IMU. As a result, controlling the two degrees of freedom of the mechanism at several points of the trajectory assures the end-effector trajectory and therefore the fingers’ range of motion, which helps for full patient recovery.

Green Fruit Removal Dynamics for Development of Robotic Green Fruit Thinning End-Effector

HighlightsPulling and stem-cutting methods were used for measuring the green fruit removal dynamics.A stem-cutting end-effector prototype was designed, developed, and tested for green fruit removal.No significant correlation was found between the fruit or stem size and the force required for fruit removal.The success rate of the stem-cutting end-effector prototype for all experiments was over 90%.Abstract. Green fruit thinning is one of the most important operations in apple production for obtaining high-quality fruit. Manual thinning is time-intensive, making it impractical for large orchards. Some alternative methods, such as chemical and mechanical thinning, have greatly improved work efficiency, but both methods have drawbacks due to non-selective targeting. Robotic green fruit thinning can potentially be as selective as manual thinning. This study developed an effective end-effector for robotic green fruit thinning. Prior to designing the end-effector, a series of fruit removal dynamics tests were conducted to determine the forces required for robotic thinning using pulling or stem-cutting methods on three different apple cultivars. The overall mean forces for pulling detachment were 24.78 ±0.48 N and 19.91 ±0.55 N when detaching stem from the fruit-end and the spur-end, respectively. The average force required for stem-cutting was 33.6 ±8.0 N among the three cultivars. No significant differences were found between the fruit or stem dimensions and the force required for fruit removal. A stem-cutting end-effector prototype was then developed to conduct fruit removal experiments in field conditions. Two end-effector prototype configurations were tested: one placing the end-effector on a handheld bar, and the other integrating the end-effector with a six DoF robotic manipulator. The success rates of green fruit removal for all end-effector prototype experiments were over 90%. The end-effector is a core component of an automated green fruit thinning system. Integration with the robotic manipulator also indicated the potential of a robotic green fruit system to remove fruit at different locations and orientations. A machine vision system will be developed and integrated with the end-effector to develop a robotic green fruit thinning system. Keywords: Apple, Crop load management, End-effector, Fruit removal dynamics, Robotic thinning.

Development of a Robotic End-Effector for Apple Tree Pruning

HighlightsAn end-effector with two degrees of freedom (2R) was developed for pruning apple trees.A rational 2×2 relationship (R2 = 0.93) was found for ‘Fuji’ apple tree branch diameter and cutting force.Simulation showed that the cutter can be aligned in a wide range of orientations in a spherical workspace.The developed end-effector was able to cut branches up to 12 mm in diameter.Abstract. Robotics and automation technologies are now used extensively in agriculture, while production operations for tree fruit crops still largely depend on manual labor. Manual pruning is a labor-intensive and costly task in apple production. Robotic pruning is a potential solution, but it involves several challenges due to the unstructured work environment. This study focused on designing an end-effector prototype for pruning considering the maneuvering, spatial, mechanical, and horticultural requirements. Branch cutting force was measured with a thin force sensor to provide guidelines for the end-effector design. The test results indicated the relationship between the force required to cut different diameter branches with an R2 value of 0.93. The end-effector was developed using two rotary motors, a pneumatic cylinder, and a pair of bypass shear blades. A three-directional linear manipulator system and a control system were built for moving the end-effector to targeted locations. A mathematical model was developed for simulation of the workspace utilization and reachable points of the end-effector. The simulation results indicated that the end-effector can be aligned in a wide range of orientations of the cutter. Field tests were conducted for validation of the simulation results and performance assessment of the end-effector. The results indicated that the end-effector with the current parameter settings successfully cut branches up to 12 mm in diameter and was able to cut branches in a wide range of possible orientations in a given 3D space. The robotic end-effector developed in this study is a core component of an automated pruning system for fruit trees. In future work, an integrated manipulator system will be developed for branch accessibility with collision-free trajectories. Keywords: Malus × domestica (Borkh.), Pruning end-effector, Reachable-points simulation, Tree pruning.

A Soft-Robotic End-Effector for Independently Actuating Endoscopic Catheters

Abstract This paper deals with the design, development, modeling, and experimental validation of a prototype endoscopic attachment that can be actuated independently by soft actuators to position an endoscopic catheter tip to a desired location. The soft actuators are miniaturized pneumatic artificial muscles (MPAMs), and by applying 137–827 kPa pressure to one or more MPAMs, the tip of the endoscopic catheter can be positioned in an approximately hemispherical region of 45 mm radius. An optimization-based forward kinematic model to predict the profile of the actuated end-effector is developed. Experiments conducted on the prototype show that the kinematics model can predict the deformation profile of the end-effector with a maximum error of 2 mm. An inverse-kinematics model to estimate the pressure required in the MPAMs to position the tip of the catheter at a specified point is also developed. The pressures in the MPAMs are controlled using an ATmel ATMega 2560 micro-controller with the inputs generated with a thumb-stick to show that real-time actuation is possible. Finally, ex-vivo experiments were conducted to show that the developed prototype end-effector can be successfully used to independently actuate endoscopic catheters.

Design and Validation of a Reconfigurable Robotic End-Effector Based on Shape Memory Alloys

Thermal shape memory alloy (SMA) actuators are known for their superior energy density (force–volume ratio) compared to other actuation principles, allowing the construction of lightweight and compact systems. Furthermore, SMA actuators can be used as sensors, as their electrical resistance changes during activation. Using this multifunctionality, this work aims at presenting the development, fabrication, and validation of an SMA-driven robotic end-effector. The end-effector prototype is designed in a modular concept and consists of four independent arms with two degrees of freedom (DOF). Each arm can rotate in-plane and also tilt out-of-plane to allow gripping of various workpiece geometries. Both DOF actuator components consist of an SMA wire working against a tension spring. The tilting joint has an additional mechanism that creates two energy-free rest positions to improve energy efficiency. The end-effector is designed to carry a maximum load of 10 kg. In a test bench for the validation of the SMA-driven end-effector joints, hall sensors are used to measure the gripping arm displacement. In addition, the resistance of the SMA wires is monitored during activation. The dynamic system performance is analyzed using different activation current levels. Finally, a proportional integral (PI) control with Hall sensor feedback is implemented to position the first DOF at arbitrary angles within its 90° rotation radius.

End-effector with a bite mode for harvesting citrus fruit in random stalk orientation environment

It is difficult for harvesting robot to harvest the citrus fruits with random stalk orientations. To harvest citrus fruits with random stalk orientations by harvesting robot, some new descriptions for the stalk orientations of citrus fruits are introduced and an end-effector with the bite mode for citrus harvesting robot is designed by simulating the head mechanism of snake. According to the end-effector, an optimization method of harvesting postures is suggested and a function to evaluate the harvesting postures is obtained. Combined with the structural parameters of end-effector and the growth orientations of factual citrus fruits, the evaluation function is applied in the harvesting of citrus fruits grown in the natural environment and the optimal harvesting posture of 46° is obtained. Based on the model of end-effector, the end-effector prototype with the bite mode is assembled and then applied in a harvesting robot. The results of cutting citrus stalks and harvesting citrus experiments in laboratory indicate that the average success rate of cutting is up to about 98% in the deflection angle range of [−50°,50°] and the harvesting rate in the optimal posture is about 89%. In addition, the harvesting results in natural environments show that the harvesting rate in the optimal posture is up to 74%. The harvesting experiments in both laboratory and natural environments demonstrate that the harvesting rate in the optimal posture is higher than other harvesting posture. The results show the designed end-effector and the method of optimizing harvesting postures are acceptable and the results can contribute to the development of next-generation citrus harvesting robots.

Mechanism for Bundling and Tying of Red Raspberry Primocanes

Abstract: In red raspberry production, two years old canes are removed every year and remaining one year old canes are bundled together to provide a firm canopy structure for next year’s crop. Currently, cane bundling and tying is completed manually, which is a highly labor intensive operation. Automation and mechanization has a potential to reduce the labor use and associated cost for this field operation. There are some bundling and tying mechanisms presently available, but most of these mechanisms are designed with post-harvest agricultural products in mind. Such mechanisms have the flexibility of utilizing change in position and orientation of the products supported by dexterous manual control. However very few mechanisms exist which are capable of bundling and tying horticultural plants or canes in a growing stage in field environment. The authors present a novel mechanism designed to work in field conditions in trellised red-raspberry production system. A hydraulically controlled cane gripping mechanism was designed, fabricated and evaluated in a red-raspberry plot, along with a tape tying end-effector prototype that was fabricated using 3D printed parts. The prototype mechanism successfully bundled and tied red-raspberry plants with up to 7 canes. Improvement and further evaluation will be carried out to accommodate plants with larger number of canes.

Preliminary Design of a Robotic System for Catching and Storing Fresh Market Apples

Abstract: This paper presents the preliminary design of a two-link planar manipulator for fresh market apple catching. Rather than use the harvesting manipulator to place picked apples in a storage container, the secondary system catches and stores apples at the point of fruit separation in order to minimize path length and improve cycle time. Monte Carlo simulations were used to select link lengths and joint limits. The design includes two low cost stepper motors and a vacuum assisted end-effector. After fabrication, laboratory studies were conducted to measure the system’s repeatability and validate the proof-of-concept. A conservative estimate of repeatability is 20 mm, which is within the catching end-effector’s effective workspace. During integrated system testing in the lab, the secondary system caught all harvested fruit. Likewise, the pick-and-catch technique resulted in an approximately 50 percent reduction in overall cycle time compared to the conventional pick-and-place method. Future work will include development of an end-effector prototype with soft elements to minimize fruit bruising.

Preliminary Design of a Three-Finger Underactuated Adaptive End Effector with a Breakaway Clutch Mechanism

<div class=""abs_img""> <img src=""[disp_template_path]/JRM/abst-image/00270005/05.jpg"" width=""300"" /> A robotic end effector prototype</div> Commercially available robotic grippers are often expensive and not easy to modify for specific purposes of robotics research and education. To extend the choice of robotic end effectors available to researchers, this paper presents the preliminary work on prototype design and analysis of a three-finger underactuated robotic end effector with a breakaway clutch mechanism suitable for research in robot manipulation of objects for industrial and service applications. Kinematic models of the finger and the breakaway clutch mechanisms are analyzed aiming to define selection criteria of design parameters. Grasping performance of the end effector prototype manufactured with a 3D printing technology and off-the-shelf components is evaluated using simulation and experimental analyses. Comparison with widely applied available robotic end effectors shows the potential advantages of the proposed end effector design. </span>

Development of space end-effector with capabilities of misalignment tolerance and soft capture based on tendon-sheath transmission system

The essential requirements of the end-effector of large space manipulator are capabilities of misalignment tolerance and soft capture. According to these requirements, an end-effector prototype combining the tendon-sheath transmission system with steel cable snaring mechanism was manufactured. An analysis method based on the coordinate transformation and the projection of key points of the mechanical interface was proposed, and it was a guideline of the end-effector design. Furthermore, the tendon-sheath transmission system was employed in the capture subassembly to reduce the inertia of the capture mechanism and enlarge the capture space. The capabilities of misalignment tolerance and soft capture were validated through the dynamic simulation in ADAMS software. The results of the capture simulation and experiment show that the end-effector has outstanding capabilities of misalignment tolerance and soft capture. The translation misalignments in radial directions are ±100 mm, and angular misalignments about pitch and yaw are ±15°.

A knot-tying end-effector for robotic hop twining

Twining is an essential but labour intensive task in high trellis hop production. Thus, there is a high demand within hop production to mechanise the operation. To mechanise the process a multi-actuator mechanical end-effector was proposed in this investigation. The prototype of the end-effector allows automated knot-tying by mimicking human hands making a clove hitch knot using a sequence of coordinated string delivery and capturing actions. A pneumatic actuating system, consisting of five pneumatic cylinders, accomplished twelve actions to tie a knot. The core in the development of this end-effector prototype development was the coordinated action planning and the control algorithms. A research prototype end-effector was built to validate the functionality, practicability and robustness of the proposed concept and control algorithms. Laboratory scale tests showed that the developed prototype could reliably tie the knot and that successful rates reached 100% and 98% with knot cycle times of 5.9 s and 4.8 s, respectively. The results indicated that the developed knot-tying end-effector could successfully tie clove hitch knots for twining in a laboratory environment. ► A multi-actuator mechanical end-effector was developed, fabricated and tested in tying knots for hop twining. ► Kinematic analysis was conducted to define the knot-tying trajectory of support the design of the device. ► Two of laboratory test sets with different cycle time per knot were analysed for assessing the success of the prototype.

Piezoelectric Tweezer-Type End Effector With Force- and Displacement-Sensing Capability

This paper presents the design and development of robotic tweezers with a force- and displacement-sensing capability driven by piezoelectric stack actuators. In order to satisfy sufficient stroke and tip force for future medical operations, a rhombus strain amplification mechanism is adopted. One of the serially connected piezoelectric stack actuators nested in the end effector is used as a force sensor. The force-displacement characteristics at the outermost layer with respect to the forces of the innermost PZT actuators (i.e., forward model) is obtained from a lumped parameter model of the rhombus strain amplification mechanism and a Bernoulli-Euler beam model of the tweezer-style end effector. The end-effector tip force and displacement are measured using an inverse model of the nested multilayer structure relating these quantities to an induced voltage across the innermost PZT actuator. The prototype end effector has the size of 69 mm (length) × 14 mm (height) × 13 mm (width). The performance test shows that the prototype has 1.0-N force and 8.8-mm displacement at the tip. The sensing accuracy was also evaluated through experiments. The experimental results show that the prototype has mean error of 0.086 N for force and 0.39 mm for displacement, which are equivalent to 11% of their maximum measurable values.

2A1-D01 知能モジュール群検証用リファレンスハードウェアの開発

In order to develop intelligent RT software components more efficiently, we are developing the reference hardware robot system for RT components research applications. This robot consists of a 6 DOF serial link manipulator unit and a 2-wheel drive vehicle unit. These units are modularized, and all users can connect some additional RT components to the system by the OpenRTM-aist development system. Furthermore it can be used for healthcare applications by mounting intelligent RT components designed for the "Service dog". In this paper, we discuss the first prototype of the robot system and the optional prototype end effector.

Development of a Canopy Volume Reduction Technique for Easy Assessment and Harvesting of Valencia Citrus Fruits

The design and evaluation of a basic end-effector prototype for automated citrus harvesting was studied. The concept can be easily incorporated into the design of an automated or a robotic citrus harvester. The concept is based on a unique canopy volume reduction approach that takes advantage of the significant flexibility associated with citrus trees. The method provides a temporary reduction in the tree canopy volume, creating space for the action of simple and potentially fast three-axis Cartesian manipulators. The action of the device also creates fruit alignment that can simplify fruit quality assessment and picking. The prototype included a remotely controlled electro-pneumatic powered clipper to cut fruit stems, two remotely controlled pneumatic cylinders, and two hydraulic powered forks to reduce the canopy volume and to guide the cutting device to a specific location inside the tree canopy. The prototype performance was assessed by the quantification of its fruit removal success rate and damage to fruit and tree canopy. The fruit location of three Valencia orange trees was entirely mapped, and the device was operated on a forklift to evaluate its performance. Field trials were conducted in citrus groves located in Davis and Dinuba, California. This simple prototype end-effector successfully harvested an average of 84% of the fruit and caused no significant damage to harvested fruits during the harvest operations. The simple prototype end-effector, developed based on the canopy volume reduction technique, showed potential to reach significant citrus fruit removal. Based on these results, a future redesign of the system may improve the canopy penetration, increase successful removal rates, and maintain negligible fruit damage.

A Robotic Mechanism for Grasping Sacks

This paper describes a novel robotic end-effector and a method for grasping deformable objects with undefined shapes and geometry, such as sacks and bags. The first prototype end-effector, designed for applications in the U.S. Postal Service, is comprised of two parallel rollers with gripping surfaces in which the rollers are pushed toward each other. When the end-effector comes into contact with any portion of the deformable object, the rollers turn inwardly so that a graspable portion of the object is dragged between the rollers. The rollers stop rotating when a graspable portion of the material/object is caught in between, allowing the object to be maneuvered by the robot. The object is released when the rollers turn outwardly. The end-effector described in this article can grab and hold filled sacks from any point on the sack, regardless of the sack's orientation. Experimental evaluation of the end-effector has proven the design and implementation remarkably effective. This article describes the hardware, control method, and design issues associated with the end-effector. Note to Practitioners - Delivery and postal services around the world currently use sacks to hold letters, magazines, and small boxes. The considerable weight of these sacks, their lack of handles, eyelets, or other operator interfaces, and the unpredictable shape and size of the packages within create awkward and uncomfortable handling predicaments for mail handlers at all U.S. Postal Service distribution centers. Currently, no robotic hand or end-effector is commercially available to grab and hold sacks effectively, so sacks must be handled manually by postal employees in distribution centers. This paper describes the design of a novel robotic end-effector for manipulating deformable objects with undefined shapes, such as sacks and bags. This device, which does not mimic human hand architecture, is simple and practical; it makes use of the friction between two rotating rollers to grab sack material when it is in close proximity of the end-effector. The rollers cease rotation when sufficient sack material is collected between the rollers to support the sack. They reverse their rotation, and turn outwardly to release the sack again. This end-effector is able to grab a sack at any point, does not require the edge of the sack to be gathered and flattened prior to grasp, does not require the sack to be placed on its bottom, needs no operator intervention, does not use the weight of the sack to lock and secure the sack in the end-effector, and does not damage the sack contents.

A Practical Robotic End-Effector for Grasping Postal Sacks

This article describes a new class of end-effectors that can be used with robotic and material handling devices for grabbing and holding deformable objects with undefined shapes such as sacks and bags. These end-effectors can grab and hold filled sacks from any point on the sack and regardless of the sack orientation and position. The first prototype end-effector, designed for the U.S. Postal Service, has two rollers. The rollers are pushed toward each other by the force of a spring. When the rollers are powered to spin, the inward spinning of the rollers causes the sack material to be dragged in between the rollers due to the friction between the surfaces of the rollers and the sack material. The spring pushes the rollers toward each other with sufficient force to hold the sack material in place between the rollers. The end-effector described here has been evaluated and proven to be exceedingly effective in grabbing and holding postal sacks. This article describes the underlying principles of the design, grasp conditions and control of the end-effector.