Virtual Prototyping
Pneumatic Muscle Actuators
Shape Memory Alloys (SMA) Actuators
Bioengineering
Finite Element Model Updating
Structural Modifications
Robotics

Small Gripper with Shape Memory Alloy Actuators (SMA)
SCARA Robot with flexible structure
Parallel Robot driven by pneumatic actuators
Parallel Robot with Shape Memory Alloy Actuators
Parallel robot with SMA actuators with internal sensor effect

The constructive solution for the realization of the mechanism consists in a structure to which the mobile elements are bound. The actuators in SMA are in number of 4 in a symmetrical disposition to avoid couples of rotation that would increase the friction strengths between sleigh and guide. For the block of the SMA actuators on the structure and on the sleigh, adjustable special systems of fixing have been developed. The fingers have the particularity to be adjustable in operation of the dimension of the object to grab. The springs are stopped on the guides through two adjustable locks to allow regulations for the correct operation. The hand has been realized in light material, Aluminium and Nylon, to limit the weights. Last phalanx are dressed in rubber to improve the conditions of gripping. The dimensions are 19 mm x 60 mm x 80 mm. The command for grip it happens with the passage of current through the actuators that develop the necessary thermal power to the deformation for Joule effect. Experimental verifications of the abilities of grip have been effected. It has been commanded gripping of objects with parallel faces and cylindrical objects with different dimensions and weights.

   

The objective is the improvement of the performances of the arms of robot looking for very small times of positioning. In these cases classical control goes to crisis for the impossibility to check the structural vibrations. It is possible to adopt innovative strategies of control that think about the vibration behaviour of the structure and that they allow fast positioning without the onset of vibrations. An opportune law kinematics is been individualized by to apply to the flexible link which is able to effect brief positioning (time = 2 fundamental period of the structure) with notable reduction of oscillations positioning. In the first figure the torque law is showed and in the second figure the comparison about the end oscillations positioning between a classical law of control and with the proposed method. It notice a reduction about 20 times of the peak-peak of the oscillation.

The robot has an architecture parallel kinematics and it’s operated with traditional pneumatic actuators. The control system is based on logical Fuzzy. It's a machine with 3 degrees of freedom (DOF) with dimensions around 2m x 0.8m x 1m. The working volume has form "lenticolar." A static characterization of the robot has been effected. It has been possible to characterize the precision of positioning and the repeatability of the robot. A specific measurement equipment has been set-up. It consist of high precision cube mounted on the moving plate of the robot, and fixed trihedral gauge with six LVDT trasducers.
They result:
Precision of positioning: 2mm
Repeatability of positioning: 5.6 mm
It has been made a model for the forecast of the dynamic behaviour of the robot. The model has been verified experimentally through measures of the frequencies proper of the structure in the different points inside the working volume. The model experimentally validate has been used for developing mapping, on the working volume, of the frequencies proper of the robot.

      

The objective of this study is the realization of a small manipulator to 3 DOF with kinematics parallel structure usable as device of orientation or for the manipulation of small objects. The robot has size of 180mm x 100mm x 100mm and a working volume of lenticular shape of the height of 2 mm and diameter of 24 mm. For the movements it has been used wires in Shape memory alloy (SMA) in Ni-Ti of the diameter of 150 micron. The structure kinematics is parallel and the wires are maintained in tension through a mechanical spring between the base plate and the moving plate. It has set a control system in closed loop. The thermal power is produced for Joule effect making to cross from current the actuators themselves. The control law is a simple proportional one and it uses a feedback signals of a position’s sensor of resistance. The kinematics architecture foresees the actuators connected to the base plate through cylindrical hinges to 120° and the moving plate with spherical hinges. This solution has realized with the actuators in isosceles triangle disposition. This configuration besides furnishing a simple constructive solution to the functional specifications, allows also an amplification of the movement of the actuators. On the base of the project the prototype of the robot has been realized. Some preliminary verifications of the movements of the single axis and pursuit of trajectories have been effected that require the control coordinated of everybody three axis.

Video of the robot (8Mb)

The objective has been the realization of a manipulator, of small dimensions, to three degrees of freedom. For the driving it has been used wires in SMA and the feedback control system it uses the internal sensor effect of the material. In this way it has been possible to realize a structure with small dimensions. They have been effectuated movements of the single axis and movements coordinated that they contemporarily involve all the axis. In the figure is showed the realized prototype.