The Design of Two Pendulums Spherical Robot

Abstract. A spherical robot driven by two pendulums is designed, which is actuated by both the eccentric force and the inertial force generated by the inner drive unit when the robot is in motion. This improved drive manner improve the eccentric mass ratio greater than the robot total mass, can provide more eccentric moment and the moment of inertia, so that the robot has a higher speed of movement. Through the analysis of movement principle and design to complete the structural model and the main components of the spherical robot design.

Key words: robot; two pendulums; spherical

Introduction

Spherical robot is a new type of mobile robot for a walk on a rolling basis, compared with the traditional wheeled foot spherical robot, spherical robot with its unique structure and movement principle. In structure, the shell of the spherical robot spherical or near-spherical, other institutions, devices are encapsulated within the sphere, and to prevent the external environment to cause damage to the components. Athletic stance when robots have been hit or fall from a height, the spherical shell is easy to adjust and recovery will not occur "overturn" the situation. Spherical robot in wet, dusty, rugged in the complex environment of the job can be used for military reconnaissance, planet exploration, disaster search and rescue missions. Movement principle, spherical robot through the movement of the internal driving unit to break the static balance of the sphere, to achieve rolling walking under the eccentric force produced by the drive unit movement and the force of inertia. The flexible spherical robot movement, with a pivot turn and all-round rolling capacity, capable of operating in a narrow space, industrial pipes, ditches, etc. can be used for detection of the narrow space environment.

In this paper, within the driver spherical robot comprehensive comparative analysis of their respective advantages and disadvantages, proposed structural model of a driving both inside and outside the spherical robot to be better able to solve the problem of energy supply and voluntary movement.

1.Design Principles

The spherical movement of the robot design principle is: the center of gravity position of the spherical robot is changed by the movement of the counterweight body, shown in Figure 1 the center of gravity to move to the point O ', the sphere system of gravity G and the face of the sphere forming a supportive FN a couple, driven spherical robot plane scrolling occurs when an obstacle in the spherical robot can adjust its position and attitude, so as to achieve the purpose of over, or avoid obstacles.

Fig 1 (Left)Left view of spherical robot .(Right) top view of Spherical robot

At startup, the motor is equipped with a weight to the move of the spherical shell, the interior of the sphere, making scrolling counterweight means in its center position. Structure, so that each member along the central axis of the spherical robot internal symmetrical arrangement, i.e., the centroid and the center of the sphere coincides, the elimination of the internal structure of the sphere omnidirectional rolling adversely affected.

2. The design of model structure

The design principle of the spherical robot: meet the requirements under the premise of minimizing the size of the sphere, and meet under the premise of the strength, stiffness, and try to use lightweight materials. This makes the spherical robot's internal drive power consumption to a minimum, in order to extend its service life. Therefore, the most important design parameter is the diameter of the outer spherical shell and the total weight of the robot, the diameter of the outer spherical shells to determine the size of the spherical robot, determines the motion performance of the total weight of the robot.

Through this calculation, the the the external airbags shell outside diameter 800 mm, wall thickness of 1 mm, spherical shell made from PVC material with higher toughness and strength; robot's total weight not exceeding 10 kg. The motor select size smaller, linear stepper motor power of 13 W, and the rational use of the stepper motor, battery pack and other internal instrument device as the internal drive mechanism moving counterweight body. Then the other parts of the size is determined according to the outer spherical and the size of the motor, these parts use the lesser quality of the hard aluminum alloy or nylon material. The various components inside the sphere are arranged symmetrically. Counterweight assembly both as a counterweight, is also a core assembly component of the drive means of the interior of the spherical robot.

Fig 2 structure design

(A) spherical robot(B) the counterweight assembly structure A1. Sphere.2. Axis screw.3. Guide rod.4. End coupling means.5. bracket.6 counterweight fixator.7-captive stepper motor.8.bracket.9. Timing Pulleys.10. Timing belt.11 batteries.12. Motor drive.13. Gyroscope.14. The main control circuit board.15. Encoder

2.2 The design of spherical robot parts structural

The load along the central axis of the screw moves in the counterweight, axis screw occurs when the bending deformation or torsional deformation. When structural design of the screw strength and stiffness. Spherical robot in the course of the campaign, when the counterweight body load vertical axis screw axis screw to withstand the force reaches the maximum. Counterweight body load for gravity load, therefore, may refer the matter is equivalent to a cross-section to the circular level Charpy withstand vertically downward concentrated load the statics model, as shown in Figure 3.

supported beam load

AC segment, set up a cross-section m-m at positive shear and positive moment for Q1 and M1, the following equilibrium equation can be obtained:

Segment BC, set up a cross-section n-n at the positive shear and positive moment for Q2 and M2, the following equilibrium equation can be obtained:

When a＞b，is |Q|max＝Pa/L，Occur in any section of the segment BC；but Mmax＝Pab/L，Occur in the cross-section corresponding to the point C of the concentrated force.

From the above analysis，when aL ，then |Q|maxP；when a＝b＝L/2 ，then Mmax＝PL/4。Therefore, according to the concentrated load P role in the situation near the end of the Charpy calculated maximum shear beam suffered Qmax, P role in Charpy midpoint position to calculate the beam suffered the maximum bending moment Mmax.

Consider the central axis of the screw installation connected inside the sphere, the establishment of the spherical robot screw length L = 700 mm, with heavy body load P = 20 N, the central axis of the screw to withstand the maximum shear force and maximum bending moment were:

Axis screw suffered shear and bending moment is calculated, the following need to determine the initial value of the central axis of the screw in diameter. τmax≤[τ], to determine the circular cross section of the smallest diameter d by the shear stress intensity conditions. Calculated as follows:

The axis screw material 45 steel quenched and tempered, allowable bending stress [σ]＝110 MPa, by bending normal stress conditions of strength σmax≤[σ] can be determined and a circular cross section minimum diameter d. Calculated as follows:

Above the maximum shear stress and the maximum bending stress calculation, as long as the same time meet the strength conditions determined by the formula (4) and formula (5), it can initially determine the circular cross section of the smallest diameter d, i.e. the central axis leadscrewdiameter, rounded to d = 7 mm. Rigidity condition is not satisfied. Therefore, to re-take d = 11mm, to meet the central axis of the screw the stiffness conditions f'max≤[f] 、θ'max≤[θ].

3.Conclusion

Based on the strength of the design of the above internal and external drive of both spherical robot structural design and analysis, as well as important parts of the spherical robot is in motion, with heavy body load P = 20 N role to meet the requirements of the strength and stiffness of the main axis screw The parameters are as follows: length L = 700 mm, to medium diameter d = 11 mm, material 45 steel quenched and tempered. These core parameters and lay a solid foundation for further internal and external drive both spherical robot.

Reference

[1] ZHENG Yi-li1，SUN Han-xu2。Dynamic modeling and kinematics characteristic analysis of spherical robot[J]. JOURNAL OF MACHINE DESIGN，2012.29（2）：25-30.

[2] ZHAO Bo，LI Man-tian，SUN Li-nin. Turning in place motion control of two pendulums driven spherical robot[J]. JOURNAL OF HARBIN INSTITUTE OF TECHNOLOGY.2011.43（11）：49-54.

[3] Halme A, Schonberg T, Wang Y. Motion control of a spherical mobile robot[C]. In 4th International Workshop on Advanced Motion Control (AMC’ 96). Japan：Mie University，1996：259-264.