With the continuous improvement of manufacturing automation, more and more attention has been paid to the automatic guided vehicle. The automatic guided vehicle is one of the intelligent wheeled mobile robots, which has many advantages such as high transportation efficiency, fast action and reliable work. However, most of the traditional automatic guided vehicles work on the hard and flat ground without obstacles, and basically have no obstacle crossing ability and climbing ability, or the ability is weak, and the ground adaptability is poor . Foot mobile robot has strong ground adaptability, but its operation efficiency is relatively low. Combined with the advantages of the two, people have designed a variety of wheel legged mobile robots. Motion stability is an important index to measure the performance of wheel legged mobile robot. At present, there are mainly static stability margin, zero torque point method, energy stability margin and so on. Reasonable gait planning and trajectory planning can not only make the robot walk according to the requirements, but also improve the stable walking ability of the robot. Therefore, the planning of gait and trajectory is of great practical significance .
In order to improve the adaptability of the automatic guided vehicle to the hard and flat ground with obstacles, a new type of wheel leg type automatic guiding car is designed in this paper. The kinematics analysis of the single leg of the car is carried out, and the foot end workspace is obtained. In order to make the car walk stably, the motion track of the car body in the process of standing up and the moving track of the car body and the foot end in the process of walking are planned, and the overall walking gait of the car is planned based on the principle of static stability margin. Finally, ADAMS software is used to simulate the motion of the car, which verifies the feasibility of the trajectory and walking gait of the plan.
2. Overall structure design
The wheel leg type automatic guide car is mainly composed of car body and legs. Among them, the car body will be installed with energy system, control system and environmental awareness system, and the legs mainly include hip, thigh, lower leg, servo electric cylinder and wheel motor. Compared with other installation methods, the front elbow and back knee has stronger ground adaptability and more stable movement. The wheel motor is installed at the end of the mechanical leg, and the trolley has three motion modes: wheel type, leg type and wheel leg hybrid type, which makes the movement more flexible.
The wheel leg type automatic guide car is used in manufacturing industry. When working in wheel mode, all servo electric cylinders are locked, and the car is driven by hub motor. This mode is applied in the process of driving on the hard and flat ground without obstacles or in the process of wheel type movement when crossing obstacles, and the maximum speed can reach 46 When working in the leg mode, each wheel hub motor is in the braking state. At this time, it can be regarded as a whole with the lower leg. The leg is driven by the servo electric cylinder to drive the car to move. When this mode is applied to the walking process on the hard and flat ground, the maximum speed can reach 7 m / min, the maximum length can be 70 mm and the height can be 65 In the wheel leg hybrid mode, the wheel hub motor provides forward power and drives the leg through the servo electric cylinder to adjust the position and posture of the car body. This mode is applied in the climbing process on the hard and flat ground without obstacles. The maximum movement speed can reach 46 M / min and the maximum slope can be 10°.
Using SolidWorks software to design the parts model of the wheel leg type automatic guide car, and assemble the assembly model of the car,
As shown in Figure 1.
3. Kinematic analysis
The kinematics analysis is carried out for the trolley in the walking mode. The D-H coordinate system of single leg is drawn according to the rules established in D-H coordinate system, as shown in Fig. 2, from which the parameters of each link and joint variable of single leg can be obtained, as shown in Table 1.
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