A Novel Hybrid Locomotion Mechanism for Small Mobile Robot

This paper presents a new design of hybrid locomotion system for mobile robots. It consist the combination of wheel and track type motion system resulting as a hybrid mechanism that includes a robot flexible and versatile interchangeable locomotion. This robot has a switchover module (Track Tensioner unit) which results the loading and unloading of track mechanism. Three wheeled locomotion mechanism help the robot to move on flat surface or path platform with high velocity and high manoeuvrability. The track system is designed for rough and unstructured path. This hybrid mobile robot will be able to work in all type of terrains.


Introduction
Robot is defined as autonomous mechanical device, which performs automated tasks either by predefined program or under human guidance, using remote control devices.The robots are mainly used as alternative to humans being to perform difficult, dirty and dangerous tasks.The family of first commercial robots, start from Ford automobile industry in 1961.The industrial robots are used in wide range of applications; but their use is limited because most of robots are stationary and operated from a fixed base.Those fixed base robots efficiently perform industrial tasks such as welding, painting, drilling, packing, assembly and transporting.By the interaction with sensors and advanced tools, mobile robots can also develop some cognizance in industrial environment instead of performing fixed tasks.Mobile robots are usually moves from place to place on the ground to perform different tasks for various applications.Better locomotion system of a mobile robot gives a greater flexibility to perform difficult and complex tasks; their mobility is classified in three main types, shown in Figure 1.Robots with effective mobility system can perform more natural tasks in which the environment is not designed especially for them.These robots can work in a human centred space and cooperate with them by sharing a workspace together.
A mobile robot needs appropriate locomotion mechanisms that enable it to move unbounded throughout its environment.In order to enhance the work ability of robots, it becomes necessary to consider efficient locomotion mechanism, mainly for outdoor applications [1].There are many possible ways, which makes the selection of a robot's approach to effective locomotion system for their design shown in Figure 2. Most of these locomotion mechanisms have been inspired by their biological counterparts, which are adapted to different environments and tasks.The hybrid locomotion mechanism seemed effective and efficient in all type of environments as compared to individual locomotion mechanism [2].The use of many locomotion modes would results an appropriate motion mechanism of robot for the persisting conditions in the work environment [3][4][5].

Figure 1. Mobile Robot mobility systems
In this paper a new design of a hybrid locomotion system for robot is presented and discussed in detail.The scope of study is to design and develop a hybrid motion mechanism used in mobile robot.The development of an effective mobility system for robots offers an intelligent alternative solution to the many problems.In this system, robot can be able to work in track, wheel and hybrid locomotive mechanism.The wheel and track system will work within interchangeable phenomena and it gives the additional flexibility to mobile robot in its motion mechanism.Further paper is organized as Section 2 introduces the existing work or research on hybrid locomotion system of mobile robot, Section 3 presents proposed system, a new design for hybrid locomotion system, Section 4 discussion about the working mechanism of new design, and Section 5 gives the conclusion of the study.

Related Work
Researchers have put their efforts to establish an efficient, versatile and high compactable mobile robot for multi environments.The major applications of such robot mostly include rescue, urban search, military, surveillance, service and industries.For achieving any task the robot should be good enough in its locomotion, control and path planning approach.A proper and efficient locomotion mechanism may be chosen for its high manoeuvrability, flexibility and stability.A single type of locomotion is not enough to be good for all type of terrains; sometimes the working environment is very complicated including not only high obstacles and deep trenches.Wheeled mechanism is good for fast and efficient motion but only on surface, legged mechanism have high adaptability for complex environments, but very difficult in mechanical design as well as control [1].So this problem can be resolved by the introduction of hybrid locomotion system.The mobile robots with multi locomotion systems would be more flexible and efficient in all kind of applications.Table 1 shows the detail of an existing type of hybrid locomotion systems, it shows the interest and focus of researchers towards the design of a perfect and appropriate locomotion mechanism.The robot locomotion system is based on track system and an extendable arm is used at front side for manipulation, same arm also used as leg.This helps the robot to move through high steps and obstacles.

[8]
2008 Hybrid (hopping + rolling) Microbots are small spherical robot use hopping, bouncing, and rolling to move in subterranean spaces for search of possible survivors.It uses highenergy-density micro fuel cells combined with low cost and lightweight DEAs.

[9]
2009 Hybrid (crawl + climbing) It is a serpentine robot, consists sequence of sliding sock locomotion modules and steering modules.The sock locomotion modules helps robot motion advances and steering module helps robot snake like bending.

[10]
2009 Hybrid (Track + wheel) Hybrid system with track and wheel mechanism, its locomotion may be in track, wheel or both.[11] 2010 Hybrid (wheel + leg) 18 DOF rat like robot used for interaction with real rat.It has 2 legs, 2 wheels.Wheels helps fast velocity of robot and leg are helpful while interaction with real rat.

[12]
2010 Hybrid (Track + Legged) Hybrid mechanisms whereby the locomotion platform and manipulator arm are designed as one entity to support both locomotion and manipulation interchangeably.Same motor used for manipulation DOF and mobile platform DOF.

[13]
2011 Hybrid (wheel + leg) 4 wheels and same wheels are used as legs when they turn to half circular shape, each leg with 2 DOF.When hip point and rim centre point become same the wheel open in full circular shape.

[14]
2011 Hybrid (wheel + leg) 4 wheeled locomotion units (each unit contain 3 wheel members), traction is developed by the two forecarriage units and two rear ones are idle.Each unit actuated by motor with epicyclical gearing system.

Development of new System
A hybrid locomotion system for mobile robot is proposed in this paper, which comprises of the wheel and track locomotion system shown in Figure 3(a), 3(b), 3(c) and Table 2.

Control System Architecture
The wireless controller device either remote or computer is used to control the robot from a far distance.The signals send from the input control unit to the receiver at robot unit as shown in Figure 4. Then the commands are communicated to the corresponding unit for response.2 DC motors connected at rear wheels to drive the wheel unit and 1 stepper motor coupled with front wheel for steering system.The track unit also driven by 2 DC motors, which coupled with track sprocket.The loading and unloading of track unit is performed by track tensioner unit and that is connected with rack and pinion mechanism, which driven by 1 stepper motor on each side.

Discussion
The working of proposed design for robot depends upon its locomotion mechanism; it consist two interchangeable mobility systems.The robot can work on wheel, track or wheel + track combined.These multi locomotion mechanisms will be helpful for mobile robot to work in all type of terrains with interchanging of mechanism.Wheel mechanism is the easy to design and control as compared to other locomotion types.It is simpler and small in terms of descriptions, but the main disadvantages of such robots is that, their function is limited to only flat and smooth surface.They are unable to work or move on unstructured or uneven terrains.Beside this it has number of advantages on smooth surface its velocity is high, energy consumption is very low, high manoeuvrability in smooth surface and its mechanical design is very simple.The robot will run on smooth path as wheel robot, the three wheels will be on contact with the ground.The front wheel work as a steering and the drive will be at rear two wheels.Robot can run on flat inclined plan by wheel mechanism, but until a limited height.The locomotion mechanism of robot switched over from wheel to track by means of track tensioner unit.The rack and pinion is used to control the ON/OFF the floating unit in contact with ground.When the robot need to run or move on rough, unstructured path or steps its mechanism will be tracked system.Because tracked mechanism is more flexible on rough surfaces with high stability.

Conclusion
It is concluded that, the new design of hybrid locomotion system of mobile robot, will be more effective and efficient in all kind of applications.The main advantages of this robot is wheel type locomotive mechanism because of this type, robot will be good enough in dynamics, kinematics nature and also with high motion velocity on smooth path.Wheel type locomotion system is more easy to design, control and manoeuvrable, but it is limited only to plain and smooth terrains.In the combination of tracked locomotion, it would be effective for rough and unstructured path.The hybrid systems are more effective and efficient as compared to the individual mobility systems in locomotion.But there control in terms of transformability from one system to another is difficult.It concluded that the mobile robots with hybrid locomotion mechanism are mostly good for all type of terrains.

Figure 2
Figure 2. Hybrid mobile robot

Figure 3 (
Figure 3 (a).Proposed design of Mobile robot

Table 1 . Summary of existing developments on hybrid mobile robot
It consist three locomotion systems, wheel, track and leg.The track flippers also work as leg.It enhances mobile robot mobility abilities.A snake like robot work on surface and under water.It has multi units connected by joint with passive wheels for drive.It can swim and crawl faster than real fish and snake.