# Motion Control Method of Bionic Robot Dog Based on Vision and Navigation Information
## 2 Materials and Methods  
### Kinematics Analysis  
The kinematic model of the bionic mechanical dog is mainly aimed at the following problems:  
1. When the relevant parameters of each mechanism of the mechanical dog's leg joints have been obtained, the coordinates of the end point of the mechanical dog's joint in the entire body coordinate system can be calculated according to the joint rotation angle, that is, the position and posture, which is a positive motion problem; and
2. When the parameters related to each mechanism of the mechanical dog's leg joints have been obtained, we can analyze the rotation angles of each joint through inverse kinematics according to the information at the end of the leg joints, which is the inverse kinematics problem. The common gaits of bionic robots mainly include crawl, trot, pace and bound. Crawl is a common gait of some reptiles. A robot in a crawling state will always have at least three legs or four legs, as shown in Figure 1. One leg is lifted, and the other three legs form a stable triangle area (FL, FR, HL) for the support leg, so the crawling gait has high stability and strong robustness. FL, FR, HL and HR represent the left foot, right foot, left hand, and right hand respectively. The motion planning problem of the bionic robot has always been a core and difficult point of robot motion. Its essence is to continuously solve and optimize a continuous path from the initial position and pose point to the final destination position and pose point according to the target movement position and geographical environment of the robot [15]. In this paper, the bionic mechanical dog is abstracted as a position and pose point, and its essence is the position and pose of the mechanical dog in the Cartesian coordinate system. Further, we believe that each pose point corresponds to the mechanical dog. One by one with the actual leg joint structure, through the analysis of each gait in the previous section, to greatly improve the walking ability of the bionic mechanical dog in a complex geographical environment, this paper uses the crawling gait as the main gait of movement. In this crawling sequence, the quadruped support phase is not considered, and the quadruped grounding phase is formed instantly after the swing phase lands. At this time, the stability of the system is greatly enhanced, but at the same time, the system reduces the running speed of the system. When the swing phase of the robot dog switches from the front left leg to the rear right leg, the center of gravity of the robot dog switches from one side of the support field to the other side. During this process, the center of gravity of the robot dog is closest to the edge of the support field. Therefore, the stability of the mechanical dog is very poor at this time. At this time, we hope to add a quadruped support phase. Similarly, when the front right leg is switched to the rear left leg, the center of gravity of the triangular support domain also switches from one side to the other side, and it is also necessary to add quadruped support. COG is the center of gravity of the bionic mechanical dog. The early static stability determination method is used to cause the projection of the COG on the ground not to  
Figure 1: Schematic diagram of crawl. exceed the closed polygon formed by the contact between the mechanical dog and the ground. Before using this criterion, it is necessary to ensure that there are enough closed polygons. This criterion was applied in robots, such as Honda's P1, in the early days and achieved good results. For a quadruped robot, such as a bionic mechanical dog, we can use the static balance stability margin, that is, static stability margin, abbreviated SSM. When the bionic mechanical dog is walking, it must ensure the distance between the COG and the closed area boundary formed by the supporting feet. The minimum distance is greater than 0, so at this time, the bionic mechanical dog must continuously adjust the COG to meet the static stability condition.