Design of the Module and Components
From the technical point of view, the design of the whole module is strictly connected to:
- • Necessity to limit the dimensions in particular the width of the element Arm2. Indeed, this dimension influences the opportunity to decrease the distance between the control sectors;
- • Dimensions of the commercial components;
- • Obtain the correct stiffness of the components needed in order to obtain the wanted performances.
Starting from the basis of the module, we have designed the frame made upof 1 mm steel sheet. This component will be produced by means of laser-cut which will allow us to obtain the flat profile. By means of banding operations we will obtain the correct shape of the frame. This component is designed so that it presents dedicated holes and grooves used to assembly the other components. Thanks to an appropriate mounting plate, it is possible to assembly the runner to the basis of the module. This plate has been designed so as to allow us to regulate the position of the module base. Thanks to these adjustments, it is possible to adjust the height and the perpendicularity of the base. On the top of the base frame there are appropriate grooves, which will allow us to fix and regulate the structure in charge of hosting and sustaining the servomotors, which will actuate the elements Arm1 and Arm2. This structure present specific holes for servomotor assembly. Between the grooves, we designed a large square cut, which allow us to obtain the space needed for the four-bar linkage mechanisms. These will connect the servomotors to the components of the planar articulated system. As regards the mentioned runner, it is a high level commercial component. This runner works with a high number of recirculating spheres, which allow us to place the base with great precision, low plays and low friction.
The other commercial components hosted in the base are the servomotors HS- 795TG for the actuation of Arm1 and Arm2. These are high performances digital servos able to provide the required torques with a total rotation angle of 180°.
On the left and right side of the frame base, two supports whose aim is to host the transmission shaft have been fixed. These components are designed to allow us to adjust the position of the shaft. To allow us to transmit the motion by means of the pulley belt system we have to host on the same axis the rotation centre of the element Arm1 and those of the primary synchronous pulley. To obtain this important feature we hinged, by means of Dacron plain bearings, the element Arm1 to the end of the shaft, thus leaving free the centre part. There, we have placed the primary synchronous pulley, which is free to rotate on the shaft. The rotation is allowed by Dacron plain bearing while looking rings prevent the axial displacements.
In order to transmit the motion from the rods of the servomotors to the components, so as to be able to move Arm1 and the primary synchronous pulley, we have used a four-bar linkage. To obtain this mechanism we have linked these components with two rods that have the same length of those connected to the servomotors. In this manner a rotation of the servomotor is transmitted to the components with the same angle value, which means with a transmission ratio equal to one. The element Arm1 presents at its lower extremities two spacers that allow us to increase the contact surface between this component and the shaft. In this way, it is possible to prevent plays during the rotation. The component Arm1 is made by two sheets of 1 mm steel. These elements will be developed by means of laser-cut which will allow us to obtain the flat profile. By means of banding operations we will obtain the correct shape of the components. The banding is needed to reduce the width of the element Arm1 in order to decrease the distance between the control sectors. We decided to design this arm by assembling sheet components in order to arrange the pulley between the sheets. In this manner, we will obtain in the meantime a compact system and a direct actuation. The distance between the sheets of which Arm1 is made up allows us to obtain the space for the transmission belt and the components needed to regulate its tension. The upper part of the arm presents specific holes that allow us to host the transmission shaft for the secondary synchronous pulley. This component is free to rotate with respect to Arm1 but is fixed, while considering Arm2. In this way a rotation of the dedicated servo is transmitted to the primary synchronous pulley by means of the four-bar linkage. Consequently, the rotation of this pulley is transmitted to the secondary synchronous pulley, and therefore, we obtain the desired rotation of the element Arm2. Also this component has been designed to be developed by two 1 mm steel sheets. The assembly distance of these two sheets is influenced by the components in charge of actuating the torsion and the tangency degrees of freedom, which are placed at the top part of Arm2. To obtain the needed width we have arranged two spacers between the sheets and the secondary synchronous pulley.
On the upper part of the element Arm2 we arranged the tilting system in charge of providing the rotations needed to obtain the strip torsion and the tangency control. The rotation needed for managing the tangency is obtained connecting the control sector directly to a small servomotor. This is hosted in a special frame designed to be connected with a hinge to the top part of Arm2. Indeed, to obtain the rotation needed for the torsion of the strip the tilting system has to rotate. This feature has been obtained by connecting this system to the top of Arm2 by means of two pivots. To actuate the rotation we used another small servomotor hosted in a seat obtained inside the top part of the element Arm2. The servo provides the tilting system with the rotation by means of a four-bar linkage mechanism.
The designed module has to translate along longitudinal direction. To obtain this displacement it will be mounted on a specific rail by means of the described runner. To control the linear position we designed a rack pinion system. The rack is placed under the rail on an adjustable support. On the lower part of the module base we mounted a specific servomotor that is able to perform continuous rotations. By means of a pinion connected to this servo we are able to perform the translation needed to control this degree of freedom.