## 5 Results and Discussion
It can be seen from Figure 11 that, when the clearance of joint B is 0.2 mm, the deviation of the running trajectory is smaller than that when the clearance is 0.5 mm. However, the overall fluctuation at 0.5 mm was slightly better than the fluctuation at 0.2 mm. Figure 12 shows the path of the journal center running in the bearing under different clearances during the operation of the SCARA robot. In Figure 12, the solid line in red represents the path of the center of the journal in an ideal joint. The blue dotted line inside the circular track composed of red solid lines indicates that the contact mode at this time belongs to the first contact mode, and there is no contact force between them. The part where the blue dotted line coincides with the red solid line represents that the current state is a continuous contact mode, and the blue dotted line belongs to a pseudo penetration mode outside the circular track. These two states can generate different contact forces between them. Figure 11: The path of the end effector geometric center in the _XOY_ plane. Figure 10: Velocity curve of the end effector along the \(X\), \(Y\), and \(Z\) axes. **(a)** The velocity curve along the \(X-\)axis in the frame \(O-XYZ\); **(b)** the velocity curve along the \(Y-\)axis in the frame \(O-XYZ\); and **(c)** the velocity curve along the \(Z-\)axis in the frame \(O-XYZ\). Figures 13-15 show the variation trend of the bearingss and journal of joint B in the \(X\) and \(Y\) directions, respectively. Figure 13 shows the change in the contact force of joint B in the \(X\) direction. By observing the ordinate of Figure 13a,b, it can be found that, when the time t is near 1.6 s and 2.5 s and the clearance is 0.5 mm, the amplitude and fluctuation of the contact force between the bearing and journal are larger. Figure 14 shows the change in the contact force of joint B in the \(Y\) direction. By observing the ordinate of Figure 14a,b, it can be found that, when the time t is near 0.2 s and 1.8 s and the clearance is 0.5 mm, the amplitude and fluctuation of the contact force between the bearing and journal are larger. Figure 15 shows the change in the contact force of joint B in the \(Z\) direction. By observing the ordinate of Figure 15a,b, it can be found that, when the time t is near 2.1 s and 2.5 s and the clearance is 0.5 mm, the amplitude and fluctuation of the contact force between the bearing and journal are larger. Figure 14: Contact force of joint B in the \(Y\) direction. (**a**) The contact force in the \(Y\) direction when both clearances are 0.2 mm and (**b**) the contact force in the \(Y\) direction when both clearances are 0.5 mm. Figure 12: The path track of the journal center inside the bearing: (**a**) the center trajectory of the journal when both clearances are 0.2 mm and (**b**) the center trajectory of the journal when both clearances are 0.5 mm. This characteristic indicates that, the larger the clearance, the greater the influence between the bearing and the journal in the joint, which will directly lead to the reduction in the operating accuracy of the SCARA robot. Then, the constant fluctuation will lead to different degrees of jitter of the end effector of the robot, all of which will decrease the stability, accuracy, and service life of the robot.