# Real-Time Tracking and Position Control of an Elastic Cable-Driven Winch System
## 5 Experiments
### Experimental Results  
In this study, \(\pm\)100 mm sine curve reference tracking control and 100 mm position control were realized, and the maximum speed limit of the system was set to 100 rpm. To increase the controllability of the system, the speed was deliberately kept low, taking into account the effects of the long cable length. Reducing the speed made the system response more manageable and resulted in smoother operation and improved control precision.  
In this section, the performance of the proposed control methods in different test scenarios is investigated. Experiments were carried out for three different loads, 0.077 kg, 0.177 kg, and 0.277 kg. The graphs presented in Figure 7 illustrate the tracking performance of the system under different payload conditions. Graphs (a), (b), and (c) correspond to Case 1 (minimum payload condition), (d), (e), and (f) represent Case 2 (medium payload condition), while (g), (h), and (i) illustrate Case 3 (maximum payload condition).  
Tracking control was implemented in three different test scenarios. In all cases, examination of the tracking response and error signal graphs revealed that the SMC method provided more precise tracking performance. As shown in Figure 7g,h, with the increase in load, the PD controller struggled to maintain accurate tracking and became ineffective  
Figure 7: Tracking response, error signal, and control signal graphs for (**a–c**) Case 1, (**d–f**) Case 2, and (**g–i**) Case 3.  
around the 12 th second. In contrast, the SMC controller remained unaffected by the increased load and continued to provide stable and reliable control. In Figure 7c,f, the control signals are analyzed, showing that SMC produces a higher magnitude signal compared to the PD controller, which contributes to improved robustness. Additionally, Figure 7i illustrates that the PD controller had difficulty maintaining control, resulting in elevated control signal amplitudes.  
As seen in Figure 8, the sum of absolute error indicates that SMC is not significantly affected by variations in load.  
The performance of the position controllers lifting the load 100 mm upward is presented in Figure 9 under medium payload conditions.  
Figure 8: The sum of absolute errors for each case.  
Figure 9: Comparison of two control methods for a 100 mm reference: position response (**a**), error signal (**b**), control signal (**c**) and motor’s torque ripples (**d**).  
An examination of the step response in Figure 9a and the positioning error in Figure 9b reveals that the SMC method provides more precise positioning compared to the PD control approach. Nevertheless, the PD controller still demonstrates an acceptable level of tracking performance. In Figure 9c, it can be observed that the control force in the SMC method is slightly increased to maintain system stability and high robustness while reducing chattering. Figure 9d illustrates the variation in acceleration ripple amplitude based on the motor's geometric frequency, derived from the motor encoder position output to analyze the motor's torque ripple behavior. This analysis demonstrated that the SMC algorithm systematically minimized acceleration ripple amplitude at specific frequencies (e.g., 35, 60, 85, and 115 cycles/rev). In contrast, the PD control algorithm generally maintained a higher and more constant ripple level.