**Abstract**

The present study evaluates the remote operability of step climbing using two connected robots that are teleoperated by individual operators. In general, a teleoperated robot is manipulated by an operator who is viewing moving images from a camera, which is one of the greatest advantages of such a system. However, robot teleoperation is not easy when a teleoperated robot is affected by the force from another robot or object. We constructed a step climbing system using two connected teleoperated robots. A theoretical analysis and the results of simulations clarified the correlations among the robot velocity, the manipulation time of the robots, and the height of the front wheels when climbing a step. The experimental results demonstrate the step climbing ability of the teleoperated robot system.

**Keywords:** cooperative step climbing, step climbing, wheeled robot, teleoperation, remote operability

### **1. Introduction**

A wheeled mechanism can be easily controlled on a flat road and excels in energy efficiency. Many wheelchairs, carts, and robots that are used in offices or houses have wheeled mechanisms. On the other hand, they face problems with the steps that are commonly found in living spaces. Wheeled mechanisms that can navigate steps or stairs have been widely researched. Such studies have examined additional legs [1, 2], a combination of an adjustable center of gravity and multiple wheels [3], special wheels [4, 5], hopping robots [6], additional driving wheel systems [7], and multiple robots that have forklift mechanisms for climbing steps [8].

We have previously reported cooperative step climbing [9] and descending [10] using two wheeled robots, and we studied step climbing using a wheelchair and a wheeled robot connected by a passive link [11]. We also investigated wheelchair step climbing support by a partner robot equipped with dual manipulators [12, 13]. The above studies were conducted using autonomous or teleoperated robots, both of which have merits and demerits. It is therefore necessary to construct a robot system that is most appropriate for the desired purpose.

The purpose of the present paper is to evaluate the performance of two connected wheeled robots that are teleoperated by individual operators. Teleoperated robots can have cameras and manipulators on their bodies that allow them to be controlled by an operator. They may also be controlled by viewing images obtained from an external camera. This ability to be controlled by humans is one of their advantages.

However, the operators need to pay close attention when robots must be operated with pinpoint precision. For example, when teleoperated robots cooperate with each other to transport an object, interactive forces caused by delays in operation act on the robots. The robots must incline to climb a step, and the interactive forces between robots are always changing. This causes errors in movement or step climbing. Thus, step climbing under control by two operators is not simple. This is therefore the subject of the present study.

The remainder of this paper is organized as follows. Section 2 describes the cooperative system, and Section 3 describes the process of climbing a step. Section 4 presents a theoretical analysis and the results of simulations. Section 5 describes the experiment and results, and Section 6 presents a discussion of the experiments. Finally, Section 7 presents the conclusion of the present paper.

**Figure 2.**

**Figure 3.**

**Figure 4.**

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*Passive link mechanism.*

*Schematic of cooperative step climbing and descending robots.*

*DOI: http://dx.doi.org/10.5772/intechopen.90162*

*Cooperative Step Climbing Using Connected Wheeled Robots and Evaluation of Remote…*

*Configuration of (a)* Robot A *and* Operator A *and (b)* Robot B *and* Operator B*.*

### **2. Cooperative step climbing robot system**

The two robots used in the present study were wheeled robots that were developed in our laboratory (**Figure 1**). Each robot has a pair of front wheels and a pair of rear wheels. The front wheels are casters, and the rear wheels are driving wheels. The robots are connected by a link mechanism, referred to herein as a passive link, and the connecting link positions have free joints. Both robots have mechanisms to change the heights of the connecting positions of the passive link. This step climbing method is affected by the positions of the passive link (see Section 3), and we determined the suitable link positions to overcome a step [14]. The robots are deployed in a forward-and-aft configuration using the link. In the present paper, we refer to the front robot as *Robot A* and the rear robot as *Robot B*. **Figure 2** shows a schematic of cooperative step climbing (see Appendix, **Tables A1** and **A2**).

**Figure 3(a)** and **(b)** shows the configuration of *Robots A* and *B*. The motors mounted on the robots are connected to a microcontroller (PIC16F873) through a motor driver circuit. The microcontrollers are connected to the robot's PC using a ZigBee module for wireless communications.

The robots have ball screw mechanisms to climb a step and are able to change the link height (see Section 3, **Figure 4**). *Robot A* has touch sensors on its back. The sensors detect the stopping position of the passive link when the operator of *Robot A* controls the link height (**Figure 4**). In the present study, the ball screw mechanism

**Figure 1.** *Robots connected by passive link.*

*Cooperative Step Climbing Using Connected Wheeled Robots and Evaluation of Remote… DOI: http://dx.doi.org/10.5772/intechopen.90162*

**Figure 2.** *Schematic of cooperative step climbing and descending robots.*

them to be controlled by an operator. They may also be controlled by viewing images obtained from an external camera. This ability to be controlled by humans is

However, the operators need to pay close attention when robots must be operated with pinpoint precision. For example, when teleoperated robots cooperate with each other to transport an object, interactive forces caused by delays in operation act on the robots. The robots must incline to climb a step, and the interactive forces between robots are always changing. This causes errors in movement or step climbing. Thus, step climbing under control by two operators is not simple. This is

The remainder of this paper is organized as follows. Section 2 describes the cooperative system, and Section 3 describes the process of climbing a step. Section 4 presents a theoretical analysis and the results of simulations. Section 5 describes the experiment and results, and Section 6 presents a discussion of the experiments.

The two robots used in the present study were wheeled robots that were developed in our laboratory (**Figure 1**). Each robot has a pair of front wheels and a pair of rear wheels. The front wheels are casters, and the rear wheels are driving wheels. The robots are connected by a link mechanism, referred to herein as a passive link, and the connecting link positions have free joints. Both robots have mechanisms to

climbing method is affected by the positions of the passive link (see Section 3), and we determined the suitable link positions to overcome a step [14]. The robots are deployed in a forward-and-aft configuration using the link. In the present paper, we refer to the front robot as *Robot A* and the rear robot as *Robot B*. **Figure 2** shows a schematic of cooperative step climbing (see Appendix, **Tables A1** and **A2**). **Figure 3(a)** and **(b)** shows the configuration of *Robots A* and *B*. The motors mounted on the robots are connected to a microcontroller (PIC16F873) through a motor driver circuit. The microcontrollers are connected to the robot's PC using a

The robots have ball screw mechanisms to climb a step and are able to change the link height (see Section 3, **Figure 4**). *Robot A* has touch sensors on its back. The sensors detect the stopping position of the passive link when the operator of *Robot A* controls the link height (**Figure 4**). In the present study, the ball screw mechanism

change the heights of the connecting positions of the passive link. This step

Finally, Section 7 presents the conclusion of the present paper.

one of their advantages.

*Industrial Robotics - New Paradigms*

therefore the subject of the present study.

**2. Cooperative step climbing robot system**

ZigBee module for wireless communications.

**Figure 1.**

**82**

*Robots connected by passive link.*

**Figure 3.** *Configuration of (a)* Robot A *and* Operator A *and (b)* Robot B *and* Operator B*.*

**Figure 4.** *Passive link mechanism.*

of *Robot A* was only used, and the operator of *Robot A* was able to control the link position using a joystick (**Figure 5**).

Each robot was teleoperated by one operator. In the present paper, we refer to the operator of *Robot A* as *Operator A* and the operator of *Robot B* as *Operator B*. The operators controlled each robot using a joystick (**Figure 5**). The robots did not have a system to communicate the information for step climbing; however the operators were able to talk to each other.

Both robots had a camera (ELECOM UCAM-E130HWH, maximum resolution: 1280 1024, frame rate: 30 fps (640 480 pixels), 10 fps (1280 1024 pixels)) on their front (**Figure 6**). The cameras are connected to the PC using USB cables, and

moving images from both cameras (**Figure 7(a)** and **(b)**) were displayed on the *PC*

*Cooperative Step Climbing Using Connected Wheeled Robots and Evaluation of Remote…*

The angles *θ<sup>A</sup>* and *θ<sup>B</sup>* in **Figure 6** are the angles of the cameras on *Robot A* and *B*, respectively. These angles were set to *θ<sup>A</sup>* ¼ 10° and *θ<sup>B</sup>* ¼ 30°, which are the angles between the robot and the step that the robots are able to see when *Robot A* or *B* inclines to climb a step. *Operators A* and *B* teleoperated each robot using only video

The proposed method uses the equilibrium of the robots during step climbing. The two connected robots climb a step sequentially. In the present study, stages 1 and 2 indicate the processes in which the front and rear wheels, respectively, of *Robot A* climb the step. Similarly, stages 3 and 4 signify the processes in which the front and rear wheels, respectively, of *Robot B* climb the step (**Figure 9**). The ascent process, as shown in <1>�<16> in **Figure 9**, is described below. The velocities of

<1> Both operators perceive the step using the moving images from the cameras

<5> The operators make the robots continue to move forward. The back wheels of *Robot A* come into contact with the step. <6> *Robot B* pushes *Robot A*. *Robot B*

on the robots (**Figure 7**). The link height of *Robot A* is set at a high position (**Figure 4**). <2> *Robot B* stops, and *Robot A* moves forward. As a result, the front wheels of *Robot A* are lifted. <3> The operators make both robots move forward while the front wheels of *Robot A* are lifted. <4> When the operators recognize that the front wheels of *Robot A* have passed over the step edge, the operators manipulate the joysticks to adjust the difference in speed between the robots, so that the front wheels of *Robot A* are placed on the upper level of the step. Here, in stages 1 and 2, if *Robot A* is faster than *Robot B*, then the tilt of *Robot A* increases. If *Robot B* is

*screens* used by the operators (**Figure 8**).

*DOI: http://dx.doi.org/10.5772/intechopen.90162*

**3. Cooperative step climbing method**

the robots are constant in the forward direction.

faster than *Robot A*, then the tilt of *Robot A* decreases.

data from the cameras.

*PC screen for robot operators.*

**Figure 8.**

**3.1 Stage 1**

**3.2 Stage 2**

**85**

**Figure 5.** *Joystick for manipulating* Robot A*.*

### **Figure 6.** *Cameras on* Robot A *and* Robot B*.*

**Figure 7.** *Moving images from (a)* Robot A *and (b)* Robot B*.*

*Cooperative Step Climbing Using Connected Wheeled Robots and Evaluation of Remote… DOI: http://dx.doi.org/10.5772/intechopen.90162*

**Figure 8.** *PC screen for robot operators.*

of *Robot A* was only used, and the operator of *Robot A* was able to control the link

Each robot was teleoperated by one operator. In the present paper, we refer to the operator of *Robot A* as *Operator A* and the operator of *Robot B* as *Operator B*. The operators controlled each robot using a joystick (**Figure 5**). The robots did not have a system to communicate the information for step climbing; however the operators

Both robots had a camera (ELECOM UCAM-E130HWH, maximum resolution: 1280 1024, frame rate: 30 fps (640 480 pixels), 10 fps (1280 1024 pixels)) on their front (**Figure 6**). The cameras are connected to the PC using USB cables, and

position using a joystick (**Figure 5**).

*Industrial Robotics - New Paradigms*

were able to talk to each other.

**Figure 5.**

**Figure 6.**

**Figure 7.**

**84**

*Joystick for manipulating* Robot A*.*

*Cameras on* Robot A *and* Robot B*.*

*Moving images from (a)* Robot A *and (b)* Robot B*.*

moving images from both cameras (**Figure 7(a)** and **(b)**) were displayed on the *PC screens* used by the operators (**Figure 8**).

The angles *θ<sup>A</sup>* and *θ<sup>B</sup>* in **Figure 6** are the angles of the cameras on *Robot A* and *B*, respectively. These angles were set to *θ<sup>A</sup>* ¼ 10° and *θ<sup>B</sup>* ¼ 30°, which are the angles between the robot and the step that the robots are able to see when *Robot A* or *B* inclines to climb a step. *Operators A* and *B* teleoperated each robot using only video data from the cameras.
