Figure 7 - uploaded by Rezia M. Molfino
Content may be subject to copyright.
Gripper with SMA wire for closure The size and position of the pulleys has been optimised to maximise the length of the SMA wires (fig. 8). Each SMA wire is 67 mm long and opens the jaw 30°.
Source publication
Teleoperation is a relatively old practice; recently new fields of intervention are born where the slave arms need to have small dimensions and high dexterity; examples are pipes inspection, rescue missions, planets exploration, minimally invasive surgery. The object of the paper is to describe the design of a miniature gripper suitable for laparos...
Context in source publication
Context 1
... effect increases the cooling time of the wires lowering the gripper opening speed. Figure 7 shows the final version of the gripper; the fixed jaw is part of the frame, in the frame are inserted the rods that support the wire pulleys. The pulleys, during the wires shortening, rotate slightly; this movement is favoured allowing clearance between the axis and the pulley. ...
Citations
... The upper jaw of the devised gripper is movable and, the lower gripping jaw is fixed to an acrylic base using standard epoxy adhesive "Araldite". Providing one movable jaw instead of two simplifies the gripper design and enhances the grasping accuracy, Filippo et al. (2004). A stainless steel torsion spring is integrated between the jaws supported by a shaft in order to exert a restoring force to close the jaw; the shaft allows the upper jaw to rotate around it. ...
End effectors like grippers find wide applications in robotic systems. Direct drive actuators like Shape Memory Alloys (SMAs) produce seemingly large linear or rotational movements of a modular actuator upon electrical heating. Mechanical work thus generated by SMAs can be harnessed to develop gripping systems with minimal moving parts. This article presents a simplest gripper actuated by SMA wire. The mechanical structure of the gripper is comprised of a pair of jaws (one movable) and an actuation means (a SMA wire and a counteracting torsion spring) for the movable jaw. Open loop and closed loop performance of the gripper are experimentally evaluated to manipulate objects of various sizes. In order to control the position of the devised gripper, a model is estimated from open loop data using system identification technique. Accurate and precise position tracking control is achieved using Pulse Width Modulation (PWM) technique.
... n et al. (2012. Examination of various SMA actuated grippers indicates that very few reports are available on the open mode gripper design. A microgripper proposed by Kyung et al. (2008) has the gripping jaws designed by two flexible hinges to open. Though the gripper was fabricated at a macro scale, this design gave a small displacement of 120 µm. Filippo et al. (2004) investigated the drawbacks posed by different actuating elements in gripper design and presented the design of a gripper in which six SMA actuator wires were employed to be mechanically parallel and electrically series in connection, to close the gripper. This design employed long lengths of SMA wire for actuation and relatively difficu ...
... The upper jaw of the devised gripper is movable and, the lower gripping jaw is fixed to an acrylic base using standard epoxy adhesive " Araldite " . Providing one movable jaw instead of two simplifies the gripper design and enhances the grasping accuracy (Filippo et al. 2004). A stainless steel torsion spring is integrated between the jaws supported by a shaft in order to exert a restoring force to close the jaw. ...
This paper proposes a new design of shape memory alloy (SMA) wire actuated gripper for open mode operation. SMA can generate smooth muscle movements during actuation which make them potentially good contenders in designing grippers. The principle of the shape memory alloy gripper is to convert the linear displacement of the SMA wire actuator into the angular displacement of the gripping jaw. Steady state analysis is performed to design the wire diameter of the bias spring for a known SMA wire. The gripper is designed to open about an angle of 22.5 when actuated using pulsating electric current from a constant current source. The safe operating power range of the gripper is determined and verified theoretically. Experimental evaluation for the uncontrolled gripper showed a rotation of 19.97. Forced cooling techniques were employed to speed up the cooling process. The gripper is simple and robust in design (single movable jaw), easy to fabricate, low cost, and exhibits wide handling capabilities like longer object handling time and handling wide sizes of objects with minimum utilization of power since power is required only to grasp and release operations.
... The objective here is to apply a single configuration of SMA wire and the bias spring for gripping in both modes of operation. The proposed gripping designs are based on the work presented as in Filippo et al. (2004). ...
Design, investigation and control of two novel Shape Memory Alloy (SMA) wire based gripping systems one operated in open mode and another in closing mode is presented in this paper. A unified design is chosen for both the gripping systems. The gripping systems use SMA wire with a counteracting torsion spring to generated two way motion. Models of the gripping systems are experimentally determined from the open loop step response. Pulse width modulation control (PWM) controller is designed to control the tip displacement of gripping finger. These controllers are compiled to track various stationary and variable (dynamic) trajectories to suit applications that can manipulate objects of varied dimensions. Experimental results show that the grippers are able to track the position rapidly and precisely.
... cm) the bias spring is dimensioned. The proposed gripper design and construction is similar to the work presented as in [2]. CAD model of the gripper is shown in Fig. 1. ...
This paper demonstrates the self-sensing behaviour of Shape Memory Alloys (SMAs) in controlling an SMA wire actuated gripper. High power-to-weight ratio, large recovery strain, low driving voltages and direct drive capability of SMA attracted considerable research attention. To make SMA more applicable to small scale robotic manipulations, its motion control using accurate self-sensing is a best alternative. The self-sensing algorithm uses sliding mode control (SMC) in this work. A self-sensing model is built by measuring the electrical resistance of SMA wire. The polyfit model facilitates to replace additional sensor and electronics for position feedback. Demonstration of the advantages gained from using self-sensing polyfit model is evident through stationary trajectory tracking control experiment. The method is accurate and precise in tracking, providing a scope for sensorless control by simplifying the control system. With the merits shown, we expect this technique can be utilized for SMA actuators in meso to micro scale applications.
... The proposed gripper design and construction is similar to the work presented as in [2]. CAD model of the gripper is shown in Fig. 1. ...
... In order to design a NiTi based gripper it is mandatory to choose suitable components, and to dimension accordingly. The proposed gripping designs are based on the work presented as in Ref. [3]. It is easier to design the resilient biasing element for a selected configuration of the NiTi fibers and angle of rotation. ...
... The upper jaw of the devised gripper is movable and, the lower gripping jaw is fixed to an acrylic base using standard epoxy adhesive "Araldite". Providing one movable jaw instead of two simplifies the gripper design and enhances the grasping accuracy [1]. A stainless steel torsion spring is integrated between the jaws supported by a shaft in order to exert a restoring force to close the jaw; the shaft allows the upper jaw to rotate around it. ...
Shape memory alloys (SMA) are the class of stimulus responsive materials which are used as actuators because of the ability in recovering their predetermined shape when subjected to an appropriate thermal procedure. This shape recovery introduces a mechanical work that can be used to produce linear or rotational movements of a modular actuator. This work presents the investigation of control algorithms for position control of a shape memory alloy actuated gripper. The transfer function model of the SMA fiber actuator is determined from the experimental open loop response. Model based proportional integral (PI), pulse width pulse amplitude modulated proportional integral (PI-PWPAM) and internal model sliding mode controller (IM-SMC) controllers are designed. The performance of these controllers is simulated for position control. The results demonstrate that the IM-SMC performs well in tracking the desired response and provides faster response.
... Cappelleri, et al. [4] designed a piezoelectric bimorph actuator for MIS instruments. Morra et al. [5] examined the performance of a set of parallel SMA (Shape Memory Alloys) wires to open a gripper while closing function was provided by a spring. Salle et al. [6] evaluated a variety of surgical grippers actuated by electromotor and SMA. ...
The actuation mechanism of the tip of an endoscopic instrument is a major problem in designing miniature scale motorized instruments, especially when a high level of functionality and multi degrees of freedom (DOF) are concerned. We evaluated the different possible actuation methods for an endoscopic needle holder and proposed a new design of hybrid local-actuation, including a micro DC motor and a piezoelectric (PZT) actuator. The DC motor provided the long movement course required for opening-closing function of the gripper while the PZT guaranteed the high gripping force required for holding the needle. A compact serial configuration was considered for the actuators, producing an overall size of 10 mm in diameter and 39 mm in length, so that it could be implemented in the limited space available. The efficacy of the design was analyzed in a simulation study, using FEM and it was shown that the needle holder is capable to apply a sufficiently high gripping force of 22 N.
... This unique behavior can be exploited to create SMA-based actuators (or positioners), and compared to other smart material-based actuators – such as piezoelectric ceramics and magnetostrictive devices – SMAs offer relatively large strain (up to 8%) and high strengthto-weight ratio (e.g., recovery stress > 500 MP a). For instance, SMA actuators find application in microrobotics [1], synthetic jets [2], minimum invasive surgery [3], [4], active endoscopes [5], and other biomedical devices [6]. Unfortunately, they exhibit significant hysteresis effect which † Graduate student. ...
... Additionally, it is well suited to compensate for positioning errors during repetitive operations. For instance, during suturing and cutting operations in minimal invasive surgery, the SMA-based surgical tool is actuated back and forth [3], [4]. Such repetitive motion of the tool enables the application of ILC techniques to learn and compensate for the hysteresis. ...
In this paper, we investigate the design of an iteration-based control algorithm combined with feedback control to address the positioning error caused by hysteresis effect in a shape memory alloy (SMA) actuator. SMA actuators offer relatively large strain (up to 8%) and high strength-to-weight ratio, and as a result, they are being exploited in minimally invasive surgery tools and microrobotics. But unfortunately, SMA actuators exhibit significant hysteresis effect which can lead to loss in positioning precision; it can cause as much as 50% error in positioning. To address the prohibitive effect of hysteresis, we study the application of an iterative-feedforward algorithm specifically designed to account for this behavior. We show that one of the major challenges with iterative- feedforward inputs for SMA actuators is the slope of the hysteresis curve at the phase transition zones (from martensite to austenite and vice versa) can be significantly large, and thus the output response can be highly sensitive to small changes in the input. As a result, iterative-feedforward input provides limited performance because at the transition zones, small changes in the input (due to noise, for example) cause the output to change significantly, thus inducing tracking error. To alleviate this problem, and to help improve the performance of the feedforward method, we consider the addition of a feedback input to add robustness. We show: (1) experimental results that demonstrate the efficacy of the method and (2) the tracking precision can be reduced by over ten times compared to just using iterative-feedforward input. In particular, the ultimate tracking error was reduced to 0.15% of the total displacement range - approximately the sensor noise level.
... The gripper is generally fabricated using a lithography-based, precision micro machining , electrical-discharge machining or laser cutting method. For higher-end-scale components (0.5–1 mm), a forceps-type design is typically adopted, and actuation can be achieved using electrical motors, pistons, miniature solenoids or SMAs in various forms (bar, spring, wire) [12][13][14]. In a typical gripper design using motorized actuators, a complete gearing system is a must. ...
... In a gripper with hydraulic piston actuation, the piston drives a shaft that is linked to jaws, acting against a counter force spring to open the gripper. This design requires a fluid feeding system, which complicates the arm architecture [12] . This can be overcome using an SMA-type piston [16]. ...
... The Ni–Ti spring acts against a counter-force steel-spring separated by a disk connected to a shaft, which is linked to the jaws enabling the gripper to open when the Ni–Ti spring is activated. The cooling time is required to deactivate the Ni–Ti spring to close the gripper [12]. Another form of SMA that can be used in a gripper is SMA wire. ...
A gripping device actuated by shape memory alloy (SMA) wire was fabricated and investigated. The actuation mechanism and the working principle of the gripping device are simple. A SMA wire was used to close the gripper during operation and a torsion spring was integrated to open the gripper when the SMA wire relaxed. Several experiments were conducted to investigate the performance of the gripping device. The aspects investigated include gripping force, response time and cyclic test number of the gripping device. It was found that factors such as driving current, torsion-spring torque, SMA wire diameter and the number of coils the SMA wire was wound had significant effects on the gripping device's performance. The gripping force was adjustable by changing the driving current. The gripping device using one coil of Ø 100 μm SMA wire with a music wire spring produced good performance and the gripping device could withstand over 1.175 million opening and closing cycles without any deterioration in its performance.
