*3.3. Response Surface Analysis*

Response surface plots were obtained using Design Expert12 software as shown in Figures 17 and 18 to further investigate the effect law of the test factors (spring spring-finger speed A, forward speed B and embedded depth C) and their interaction on the test fingers (loss rate, wounded potato rate).

Figure 17 shows the loss rate Y1 interaction factor response surface analysis. Decreasing the spring-finger speed A and decreasing the forward speed B can reduce the loss rate; however, when the loss rate reaches an extreme point, the loss rate increases as the speed A of the picking gears and the forward speed B of the machine decrease. Decreasing the embedded depth C and increasing the spring-finger speed A can reduce the loss rate; after the loss rate reaches the extreme value, the loss rate will increase as the spring-finger speed A increases and the embedded depth C decreases. Moreover, increasing the forward speed B and decreasing the embedded depth C can help reduce the loss rate; however, when the loss rate reaches a very small value, the loss rate will increase as the forward speed B increases and the embedded depth C decreases.

**Figure 17.** Loss rate interaction factor response surface analysis: (**a**) response surface plot of the effect of spring-finger speed and forward speed on the interaction of the loss rate (**b**) contour plot of the interaction between spring-finger speed and forward speed on the loss rate (**c**) response surface diagram of the interaction between spring-finger speed and embedded depth on the loss rate (**d**) contour plot of the interaction between spring-finger speed and embedded depth on the loss rate (**e**) response surface plot of the interaction between forward speed and embedded depth on the loss rate (**f**) contour plot of the interaction between forward speed and embedded depth on the loss rate.

**Figure 18.** Response surface analysis of interactive factors on the wounded potato rate: (**a**) response surface plot of the effect of spring-finger speed and forward speed on the interaction of the wounded potato rate (**b**) contour plot of the interaction between spring-finger speed and forward speed on the wounded potato rate (**c**) response surface diagram of the interaction between spring-finger speed and embedded depth on the wounded potato rate (**d**) contour plot of the interaction between spring-finger speed and embedded depth on the wounded potato rate (**e**) response surface plot of the interaction between forward speed and embedded depth on the wounded potato rate (**f**) contour plot of the interaction between forward speed and embedded depth on the wounded potato rate.

Figure 18 shows the response surface analysis of the interaction factors for wounded potato rate. It can be seen that reducing the forward speed B and the spring-finger speed A helps to reduce the wounded potato rate. Decreasing the rotational speed of the spring spring-finger A and increasing the embedded depth C reduces the rate of wounded potatoes. Increasing the embedded depth C and decreasing the forward speed B helps to reduce the woundedness rate; however, when the wounded rate reaches a very small value, continuing

to decrease the forward speed B and continuing to increase the embedded depth C causes the woundedness rate to gradually increase.
