# Design and Analysis of a Novel Variable Stiffness Joint Based on Leaf Springs
## 3 Overall Structural Design of VSJ  
The structural design of the reconfigurable compliant robotic joint is shown in Figure 10. It includes a securing case, input section, variable stiffness module, and an output section. The input and output sections are connected in series through the variable stiffness module. The input section includes the main drive frame (part 6) and the drive disc (part 5). The two ends of this main drive frame are mounted inside the barrel-shaped securing case (part 8) via the use of bearings (part 7). The drive disc is fixed to the lower end of the main drive frame. The variable stiffness module and the main drive frame can be considered as one component. The output section is the output disc (part 10), which is mounted inside the main drive frame via a bearing (part 9). The drive disc and output disc are connected by a variable stiffness transmission section, which is located inside the main drive frame. The drive disc (part 5) is sleeved with a large timing pulley (part 3), which is connected to the  
Figure 8: Theoretical elastic potential energy characteristics. Figure 9: Variable stiffness damping torque characteristics. small timing pulley (part 2) via a timing belt (part 4). The small timing pulley is coaxially connected to the drive motor (part 1). As shown in Figure 11, the variable stiffness section includes a compliant stiffness adjustment device, positioned near the drive disc, and a stiffness/load reconfiguration device near the output disc. The transmission disc (part 14) with \(N\) evenly distributed radial slots is fixed in the middle of the main drive frame. The slider (part 15) with a columnar slide block at the lower end is arranged perpendicularly to the transmission disc, meaning it is able to slide radially along the slot. The stiffness regulation disc (part 13) with \(N\) arcuate slots in a gradually opening linear shape is installed at the lower part of the transmission disc. Sliding pairs are formed by inserting the slide blocks into the corresponding arcuate slots. The stiffness regulation disc is connected to the stiffness adjustment motor (part 11 and part 12) installed in the middle of the drive disc (part 5). The transmission disc, stiffness regulation disc, and motor located at the middle of the drive disc are coaxially connected. Figure 11: CAD model of the continuous variable stiffness mechanism: 13—adjustment disc; 14—transmission disc; 15—slider; 16—minature slide rail. Figure 10: CAD model of the joint. (**a**) Partial sectional view. (**b**) Half sectional view of main drive frame: 1—Drive motor; 2—Small timing pulley; 3—Large timing pulley; 4—Timing belt; 5—Drive disc; 6—Main drive frame; 7—Bearing; 8—Securing case; 9—Bearing; 10—Output disc; 11—Stiffness adjustment motor; 12—Reducer; 13—Stiffness regulation disc; 14—Transmission disc; 15—Slider; 16—Micro slide rail; 17—Leaf spring; 18—Screw end cap; 19—Support column; 20—Leaf spring seat; 21—Screw; 22—Lower end cover. Considering the frictional force between the slider and the linear slot of the transmission disc, corresponding miniature rails (part 16) are installed in the linear slots of the transmission disc, thus reducing the influence of frictional force on its movement, and avoiding jamming. During the operation of the stiffness adjustment module, the servo motor actuates the rotation of the adjustment disc. This instigates a radial displacement of the slider within the linear slot of the input frame. Consequently, the interaction point between the slider and the leaf spring changes, which modifies the effective working length of the leaf spring. Under load conditions, this results in the differential deflection of the leaf spring, thereby inducing a change in the joint's stiffness parameter \(K\). As shown in Figure 12, the stiffness/load reconfiguration device includes a support column (Part 19), which extends from the center of the output disc (Part 10) towards the main drive frame, as well as a leaf spring reconfiguration mechanism, which is configured around the support column.