The Prototype and the Desktop Station
To test the real performance of the designed device, we have developed a prototype made up of three identical modules.
The base is made of an anodised aluminium frame, which hosts the servomotor in charge of moving the element Arm1 and the runner. By means of a connection plate made of anodised aluminium, the servomotor is able to translate the whole module along the longitudinal degree of freedom. The element Arm1 has been obtained by assembling two aluminium forks by means of two high stiffness beams. The lower fork is connected to the rod of the servomotor realizing the hinge needed to move the element Arml. The upper fork is connected to the servomotor in charge of moving the element Arm2, which is hosted in an anodised aluminium frame similar to that one used for the module base. The element Arm2 is obtained from a square section aluminium tube fixed to the upper face of the servomotor frame. On the upper end of the stem two supports have been assembled. They create a small fork, which allow us to obtain the space needed to mount the frame hosting the servomotor in charge of controlling the local curvature. To obtain the actuation system responsible for controlling the torsional degree of freedom, the servomotor is mounted in a dedicated housing and connected to the tilting frame by means of a four-bare linkage mechanism.
The micro servomotor in charge of controlling the local curvature is hosted and fixed inside the dedicated frame that is obtained by means of an aluminium rectangular section tube. Its pinion is equipped with a connection rod that is connected to the strip support. This support is made of brass and obtained by means of soldering process. As described during the design process, the upper part of the support is equipped with two carriage obtained by means of micro ball bearing, which allow the control sector to slide on the strip. To obtain an isotactic system, the central module has not to be equipped with sliding sector but with a component that does not allow to the strip to slide. To develop this component, the bearings are substituted with miniaturized profiles that prevent the longitudinal sliding of the strip.
By assembling all the described elements, it has been possible to obtain the final prototype of the whole module (Fig. 6.5).
Fig. 6.5 Module prototype
Fig. 6.6 Base frame, rails and adjustable racks
After having developed each module of the prototype, it has been possible to assembly a variable number of modules in order to obtain the tactile station. To allow the modules to work together a common frame is needed. To obtain this structure the twin rails, which are needed to allow the alternate module disposition, are mounted on two pillars that are fixed on the station base. Each pillar is composed of two aluminium plates arranged in order to obtain a vertical free space. It is needed to mount the racks needed for the longitudinal translation. The designed configuration allows us to adjust the vertical position of the racks. This regulation is needed so as to allow mounting the modules on the rail and to ensure the correct contact between the racks and the translational pinions. The developed components are shown in Fig. 6.6.
The base frame is mounted on a desktop base obtained from some commercial profiles and a Plexiglas plate. The space obtained under this plate is used to arrange the components needed for the system control and the power supply.
The power supply is connected to the mains and converts the electricity from 220 V AC to the value needed for the servomotors, that is a value ranging between 4.8 and 6.0 V DC. The output cables of the power supply are connected to the servo controller input, which are in charge of providing the servomotors with the power. The servo controller is connected to the PC/laptop by means of two USB connections. The first is needed to provide with the Logic Voltage the controller, which is used to isolate the logic from the Servo Power Input. The second is the Serial/USB connection needed
Fig. 6.7 Station base, control and power supply components
to allow the PC/Laptop to communicate with the servo controller and, therefore, to control the servomotors. All the described components are showed in Fig.6.7.
By defining the needed number of modules and by mounting them on the rails, it is possible to obtain the designed tactile device. By mounting the three developed modules on the frame base, it is possible to obtain the final version of the tactile device prototype.