Home Engineering Tactile Display for Virtual 3D Shape Rendering
Design of the Module
To obtain the desired characteristics we have designed a new configuration of the module where:
In order to make easier the understanding of the whole system, it is useful to present, since the very beginning, all the components of the system (Fig. 6.2).
The base of the module has been made by assembling all the components needed on the servomotor frame. This is part of a system that allow us to obtain the hinge in charge of allowing the rotation needed for moving the element Arml. The frame is a clamp, which is bended to host the servomotor, and presents some holes that aims at fixing other components. The servomotor in charge of actuating the element Arm1 is fixed by means of the small flags.
On the opposite side of the frame, we have assembled the runner in charge of allowing the longitudinal translation. By means of a connection plate, we have assembled
Fig. 6.2 Preview of second version of the module the servomotor in charge of performing the longitudinal translation. The designed base presents dimension that are 15% lower than the first solution. This feature will allow us to decrease the distance between two adjacent modules, thus enhancing the resolution of the system.
To obtain the hinge in charge of allowing the rotation of the element Arm1, we used a miniaturised ball bearing, which is fixed to the servomotor frame. To allow us to obtain a correct hinge, the bearing has to be coaxial with the servomotor pinion. The element Arm1 is realized by assembling two forks by means of two high stiffness beams. On the lower part of the structure, we have mounted a rod. This will connect the servomotor with the lover fork. On the other side of the fork there is an apposite hole in charge of connecting the element Arm1 with the bearing. In this manner we have obtained the needed hinge and the rotation of the servomotor hosted in the module base is perfectly transmitted to the element Arml. The upper fork of the element presents the same configuration of the lower one, therefore allowing us to obtain the hinge needed for the rotation of Arm2. The difference between the two rotational degrees of freedom is that in Arm1 the servomotor is grounded and the forks rotates, while in Arm2 the upper fork is the frame and the servomotor rotate on its axis, thus performing the rotation needed to move the element Arm2.
The element Arm1 presents a higher width compared with the first solution. This is not a constructional constrain but our design choice. Indeed, by analysing the characteristics of the first solution we noticed that the distance between two adjoined modules is influenced by the width of the basis. On the other hand, the distance between two opposite modules is influenced by the width of the element Arm2 and of the tilting system. Thanks to the planar articulated configuration system the element Arm1 is always placed in a divergent position, which avoids collisions with the other members. Therefore, it is not needed to limit the size of the element Arml. For this reason, we have designed the arm using all the space allowed by the base width, thus obtaining an element with a high value of stiffness without threatening the resolution and the dimensions of the whole system.
The secondary fork of the element Arm1 is connected with the joint in charge of performing the rotation needed to move the element Arm2. In order to obtain this hinge, one side of the fork has been connected to the servomotor hosted at the base of Arm2 by means of a connection rod. The second side is connected by means of a miniaturised ball bearing. These components are assembled in the servomotor frame, in a way that is similar to that used for the module base. The element Arm2 is composed by a steam obtained from a square section tube fixed to the upper face of the servomotor frame by two connexion elements. These allow us to obtain an assembly with high stiffness characteristics. The stem provides the holes needed for the connections and two rectangular cuts. The upper one allows obtaining the space needed to host the micro servomotor in charge of actuating the torsional degree of freedom. The lower one is a passage for the servomotors cable. Indeed, the servomotors in charge of controlling the torsional and tangential degree of freedom are provided with alimentation and control cable. The latter has to be hosted in a safety place in order to avoid the contact with the moving elements. As a consequence, these cables will be arranged inside the steam and will be extracted through the lower passage.
On the upper end of the stem, two supports that create a small fork have been assembled. They allow us to obtain the space needed to host the tilting system. These elements are equipped with holes useful to obtain the seat for the bearings. We have designed the system in this way because it can be easily assembled and allow us to obtain the correct space needed to perform the rotation of the tilting system without mechanical plays. The frame in charge of hosting the servomotorfor torsion actuation is equipped with two miniaturised ball bearings. After having assembled these bearings, it will be possible to realize the hinge needed for the torsional rotation. The connection screw of the left bearing is equipped with a rod, placed at its extremity. This is connected by means of a rocker arm to the primary rod, which is mounted on the miniaturised servomotor. In this way, we have designed the four-bar linkage needed to transfer the torsional rotation from the servomotor to the control sector. The rocker arm is obtained by assembling two small forks with a stem. The forks are equipped with specific threaded holes and the stem presents threaded extremities. In this way, we can assembly the rocker arm and adjust its length in order to obtain the correct configuration of the four-bar linkage connection.
The frame in charge of hosting the servomotor presents 3 holes: two of them are needed in order to mount the servo and the third one is necessary in order to let the pinion passing through it. These are designed in order to allow the rotation axes of torsional and tangential degrees of freedom to lie on the same plane. Therefore, the axis of the servomotor pinion and the axis of the bearings have to be coplanar. In this way, we will obtain the wanted joint. The micro servomotor in charge of controlling the local curvature is hosted and fixed inside a specific frame. Its pinion is equipped with a connection rod. On the opposite side of the frame we fixed a plain bearing, which is coaxial with the pinion. The bearing allows the strip support to rotate according to the rotations of the servo. This has enabled us to obtain the actuation mechanism for the tangential degree of freedom. The support for the strip is made of brass and it is obtained by means of the soldering process. It has been designed to change its width according to the servomotor frame dimensions and the width of the strip, which is 30 mm. The upper part of the support is equipped with two carriages obtained by a micro ball bearing. These components present the possibility of adjusting the distance between the face of the bearing and the holding plate. So, we can mount the strip between the plate and the bearing and regulate the distance so as to provide the contact. Thanks to this design we have obtained the sliding control sector, which is able to slide on the strip thanks to the bearings and, in the meanwhile, to control the local curvature thanks to the contact between the plate and the strip.
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