# Realisation of a Novel Functionally Redundant Actuation System for a Railway Track-Switch
## 2 Switch Description and Experimental Setup  
The experimental switch panel can be seen in Figure 2. It is driven by three functionally identical (yellow) actuator bearers; otherwise, it is a conventional switch panel installed on concrete sleepers (note that, other sleepers could be used if desired). Each steel hollow actuator bearer, B1, B2 and B3, houses two identical sets of servo motors, bevel gearboxes, cams, sensors and locking elements, as shown and labelled in the 3D models of Figure 3.  
Referring to the actuator bearer diagram of Figure 3a it is possible to see the rail carrier (4), to which the switch rails are attached, resting upon the locking blocks (3) at both ends, and with the actuator cams and motors in the background (1) and (2), respectively. Figure 3b shows these latter two more clearly. Including the moving contact-bearing part of the cam just to the right on both cam housing.  
There are two key functions of each of the three actuator bearers: locking and actuation. For the lock, the locking blocks (3) ensure that the rail carrier (4) cannot move horizontally when the carrier is in the down position (with the cams at \(0^{\circ}\) or \(180^{\circ}\)). This is called \"passive locking\" as there is no separately actuated lock mechanism; the only way to unlock is by raising the rail carrier off the locking blocks. For the actuation, when driven the rail carrier (4) is driven by the cams (2) it moves in a semi-circular path (in this case anti-clockwise). The two cams are driven by the electrical motors via a speed-reduction level gearbox (1). The two motors and associated cam angles are controlled together to complete the  
Figure 2: REPOINT-Light track switch at great central railway Quorn and Woodhouse station, UK: 1. Stock rails, 2. Movable switch rails, 3. Common crossing, 4. Check rails, 5. Actuator bearer with locking elements, 6. Rail detection sensors, 7. Bearer coves, 8. Connections between the control unit and bearer elements, 9. Control unit.  
mechanical movement of the rail carrier. Hence, a key control challenge in this mechatronic actuator is to ensure synchronised motion of the two electric motors to prevent the tilting of the rail carrier. Of course, the switch panel has three of these actuators (see Figure 2), therefore the second control challenge is to ensure synchronised motion of all three actuator bearers. This is important so that the bending of the switch rails is correct along the length of the switch panel.  
The overall position of the switch rails is confirmed by two sets of sensors in each bearer; encoders on the cams determine their position and Hall-effect sensors mounted in the top at both sides of the actuator bearer that detect the presence (or absence) of the switch rail foot in either the normal or reverse position. Note that, the system is designed so that, at the lowered positions of the rail carrier, it rests on the locking blocks, (3 in Figure 3a). As the locking blocks are positioned at angles of \(2^{\circ}\) rotation and \(178^{\circ}\) rotation the rail carrier will rest on them and remain out of contact with the cams (when they are at \(0^{\circ}\) and \(180^{\circ}\)). Hence, the cam does not experience any load when the train passes over the rail in the lowered positions.