3D Printed Biped Walking Robot

Transcription

1 3D Printed Biped Walking Robot Tadeusz Mikolajczyk 1,a *, Alberto Borboni 2,b, Xianwen Kong 3,c, Tomasz Malinowski 1,d and Adrian Olaru 4,e 1 UTP University of Technology and Life Sciences, Bydgoszcz, Poland 2 University of Brescia - Mechanical and Industrial Department, Brescia, Italy 3 Heriot-Watt University, Edinburgh, United Kingdom 4 University Politechnica of Bucharest, Romania a tami@utp.edu.pl, b alberto.borboni@unibs.it, c x.kong@hw.ac.uk, d techniczny.tomasz@gmail.com, e aolaru_51@ymail.com Keywords: mobile robot, walking robot, center of gravity, kinematical analysis Abstract. The purpose of this paper is not to elaborate the bionic pattern of walking robot, but to elaborate our own simple idea of a 4 degree of freedom (DOF) walking robot with the ability to walk on flat surfaces, rotate and climbing upstairs, which is composed of vertical moved legs with a rotary foot and a controlled mass for stabilizing. In this paper, based on the former idea, a prototype model of a 3-DOF walking robot is presented for walking only on flat surfaces. This walking robot is actuated by servo motors. The paper covers the kinematics, centre of gravity analysis, description of the robot and its control system made using Pololu controller. Experiments confirmed the feasibility of the proposed design. Introduction Existing models of bionic-inspired walking robots [1] are complex and difficult to control [1,2], while mobile robots equipped with wheel are uncomplicated [3,4]. One of the most important tasks of a walking robot is to climb up the stairs. Researchers have come up with many solutions of bionic-inspired robots. Some of them are equipped with legs [1], even a special wheel [7,8] or another constructions [7]. One of the most effective walking robots, the well-known Asimo robot [1], might resemble a human body. The load carrying capability of a biped robot is quite limited since the two feet of a walking robot supports the robot alternatively during walking. Novel biped walking robot [7] based on a 2-UPU+2-UU parallel mechanism. Experiments with a physical prototype show that the novel biped walking robot can walk stably on smooth terrain. Recently, the authors of this paper presented a simple 4-DOF two-legged robot in [8]. Both legs of the robot are each connected to the body by a prismatic joint and are moved simultaneously by a single motor, which is responsible for lifting the legs. Two more motors are then responsible for the rotation of the two legs respectively. Each leg can also rotate about its vertical axis both clockwise and counter clockwise. Moreover, this robot is equipped with a stabilizing mass to ensure stability during leg movement. The mass is controlled using yet another motor. In total, the robot has four DOF. The rotation of the robot body allows it to execute a first step. Then the robot leaves the first leg and is ready for the next step using the second leg. At the same time, a coordinated movement of the mass balances the robot. It is apparent that this mechanism is much simpler and easier to control than the other existing walking robots [1]. A simplified prototype model of this kind of walking robot with 3-DOF was presented by the authors in [8]. In this design the stabilizing mass moves at the same time as the legs and this robot is only suitable for walking tasks. In this paper, was present the 3DOF solution of walking robot made using 3D printing technology.

2 Balancing of the walking robot with rotary feet For the purposes of research, a simplified model of the robot (walking only over the flat area) was developed (Fig. 1). The robot is equipped with two legs connected to the body with a prismatic joint. These legs are driven by one motor so that they move in the opposite directions. The foot of each leg can turn independently under the actuation of a servo motor. The angles of rotation of the right and left legs are defined as 1 and 2 respectively (Fig.2). In order to stabilize the robot, a stabilizing mass was applied in order to keep the center of gravity of the robot including the stabilizing mass falls on the foot on the ground. The stabilizing mass was fastened on the arm, connected to the axis of the servo motors that control the legs. It is noted that an appropriate velocity ratio must be used in order to stabilize the robot. The stabilizing mass usually moves much faster than the leg. Fig. 1. An idea of 3-DOF walking robot [9] Striding of the robot consists in the sequence of movements: the left leg moves down with the right leg moving up, and the stability mass moves to the left foot, the left foot turns about its vertical axis by 2, the left leg moves up with the right leg moving down, and the stability mass moved to the right foot, the right foot turns about its vertical axis by angle 1. When stopped, the feet of robot stand at an equal level, and stabilizing mass is at the neutral location (the center). The proposed concept enables one to control not only the length of the step by changing the angle of rotation of the foot, but also the speed of movement by changing the angular velocity of foot rotation. Therefore, this robot has excellent maneuverability [9]: ability to change the movement direction, turn back possibility. Due to the applied simplification (lack of independent control of the stability mass), the walking robot is unable to climb up the stairs.. The vertical movement of parts of the robot, and the displacement of the center of gravity was analyzed in a non-inertial reference frame (Fig. 3) [9]. The movement of all parts in this plane depends on the position of the central gear, which is described by the t angle (Fig. 1). The x coordinate of stabilizing mass is equal to [9]: r r sin (1) x' m Fig. 2. Example of robot move in y axis direction If the robot is correctly balanced, its center of gravity at the initial moment is located in the plane of symmetry (see Fig. 3a). During the movement, x coordinate of the center of gravity changes (Fig. 3b) and can be found using the following equation [9]:

3 C x ' mr 4 m sin (2) mass of the robot Fig. 3. Move robots center of gravity [9]: a) the center of gravity in between feet axes (Cx=0), b) displacement of the center of gravity to left The progressive movement of the robot will be analyzed based on an xy inertial reference frame (see Fig. 1). For linear motion, the sum of angles of rotation of both feet, 1 and 2 should be equal to zero. Otherwise the robot will turn for an angle of 1 2. The complex motion sequence makes it difficult to determining the momentary velocity. However the average speed can be easily calculated: 1 3L sin 2 vy (3) time of the entire cycle Virtual model of the robot and its control system Based on the presented concept (Fig. 1) and conclusions drawn from the analysis, a detailed design of the walking robot was created (Fig. 4,5). The construction of the robot was developed taking into account the possibility of 3D printing technology. Robotic legs are identical and connected with a rack and pinion drive. Robot legs have sliding bearing in the robot body. Combined with the body, the robot servo gear drives leg movement through racks. The axis of this servo arm was fixed to the combined balancing weight, which was made as a head containing a battery-powered robot control system. Fig. 4. 2D CAD model of robot Fig. 5. Virtual model of walking robot The legs of the robot are each equipped with a servo connected to the disc-shaped element forming the foot. The fabricated system consists of a small number of items, includes all the technological holes for mounting the robot screw elements. The solution enables the robot to act in

4 accordance with the proposed rule action. With the rising of the legs, the stabilizing mass moves rapidly to ensure the center of gravity of the entire system is over the foot of the opposite leg which supports the robot. The servo control system by the company Pololu (Fig. 6) was used to control the walking robot. A small (22x11,5x27 mm) servo mechanism SG90 was also used. Its weight is 9g, the torque is equal to 18 Ncm, and velocity is equal to 60 o /0.1s (4,8V). This controller is embedded within the body of the robot. A CAD model of the robot has been saved as a stl file for the implementation of 3D print technology. To fabricate the model, a 3D printer robot system Delta (Fig. 7) kind of Rostock [11] was used with properties: minimum value thickness of layer 0.1 mm, workspace: cylinder d=195mm, z=200mm, filament 1.7 mm. Fig. 6. Micro Maestro 6-channel USB servo controller bottom view [10] Fig. 7. Used Delta type 3D printer Testing After all the parts of the robots had been made using PLA material, the prototype was assembled (Fig. 8). Using the Pololu inner script control program, a series of tests was conducted and confirmed the ability to control the speed of the robot, as well as presented its good maneuverability such as turning. The developed system had good stability due to that the rapid movement of the stabilizing mass that helped to stabilize the robot on one foot while raising the other leg (Fig. 8). Fig. 8. Phases of move of 3D printed walking robot balancing on: a) right leg, b) left leg

5 Conclusions The 3-DOF walking robot presented in this paper has a simple structure. It has the ability to move on flat surfaces, change direction, and to rotate in any direction by any angle. The design is characterized by the use of a stabilizing mass, vertical motion of leg and rotation of feet. The prototype made using 3D printing technology is very small but the walking robot idea can be executed in different scales. The preliminary analysis indicates a great functional potential of a kinematic robot with a simple structure. This study provides a basis for further work on the robot and its control systems. More research on the launch control system including distance sensors is highly recommended. This work is the first stage to build the walking robot with rotating feet for climbing up stairs. The feasibility of moving this model on flat surfaces and ability to control direction of its movement in a simple manner has been demonstrated. Application of the machine of this type can be very broad. Due to the simple structure, its cost will be low. The cost of the robots control system will depend on how the robot is supposed to interact with the environment, which might require a computer for the control system. It has been demonstrated that it is possible to control this robot using Pololu microprocessor, which can resolve task to control of move and read of sensor inputs. It is possible to use more advanced microprocessor of the ATMEGA type [12]. The project requires further work in order to depict the practical implementation of the robot model in large scale and to build the ultimate robot model with heavy traffic jump linear foot for the verification of stair climbing. References [1] (Rabbit, QRIO, Asimo, P3, Aibo, City Climber) [2] M. Vagaš, M. Hajduk, J. Semjon, L. Koukolová and R. Jánoš, View to the Current State of Robotics, Advanced Materials Research, (2012) [3] T. Mikolajczyk, J. Musial, L. Romanowski, A. Domagalski, L. Kamieniecki and M. Murawski, Multipurpose Mobile Robot, Applied Mechanics and Materials, 282 (2013) [4] R. Jánoš, M. Hajduk, J. Semjon and L. Šidlovská, Design of Hybrid Mobile Service Robot, Applied Mechanics and Materials, 245 (2012) [5] M. Eich, F. Grimminger and F. Kirchner, A Versatile Stair-Climbing Robot for Search and Rescue Applications, Proceedings of the 2008 IEEE International Workshop on Safety, Security and Rescue Robotics Sendai, Japan, (2008) [6] A. S. Boxerbaum, M. A. Klein, R. Bachmann, R. D. Quinn, R. Harkins and R. Vaidyanathan, Design of a Semi-Autonomous Hybrid Mobility Surf-Zone Robot, 2009 IEEE/ASME International Conference on Advanced Intelligent Mechatronics, Singapore, (2009) [7] Z. Miao, Y. Yao and X. Kong, Biped Walking Robot Based on a 2-UPU+2-UU Parallel Mechanism. Chinese Journal of Mechanical Engineering, 27 (2014) [8] T. Mikolajczyk, T. Malinowski, T. Fas and L. Romanowski, New Solution for Walking Robot. Applied Mechanics and Materials, 555 (2014) [9] T. Mikolajczyk, T. Malinowski, T. Fas and L. Romanowski, Prototype Model of Walking Robot. Applied Mechanics and Materials, 613 (2014) [10] [11] [12] T. Malinowski, T. Mikolajczyk and A. Olaru, Control of Articulated Manipulator Model using ATMEGA16, Applied Mechanics and Materials, 555 (2014)