# Remote-Controlled Method with Force and Visual Assists Based on Time to Collision for Mobile Robot
## 1 Introduction  
The technology of autonomous and remote-controlled mobile robots has become more popular for various situations and objectives. Autonomous robots used in service situations have been studied to assist in human tasks [1; 2; 3; 4]. In the industry context, path planning methods with collision avoidance have been studied [5; 6; 7; 8]. Therefore, autonomous robots have been mainly used in constructed environments, such as for motion tracking, cleaning inside a building, and manufacturing robots in an assembly line [9; 10; 11]. However, there are several situations in which autonomous robots do not work properly in an unconstructed environment that requires flexibility. For an unconstructed environment such as an investigation in military and civilian fields, remote-controlled robots have been mainly used because humans can operate remote-controlled robots flexibly [12; 13]. In the field of healthcare, remote-controlled robots have been investigated to support hospital staff [14; 15]. In an industry scenario, remote-controlled robots that investigate and track complex environments have been developed [16; 17; 18; 19]. In life care, remote-controlled robots have been utilized to assist humans [20]. Furthermore, in situations of disaster response and hazardous areas, remote-controlled robots have been widely used for inspection [21; 22; 23]. These remote-controlled robots allow us to complete a variety of activities based on the operator's judgment. A monitor and a control device are used for the remote-controlled system. The operator operates the remote-controlled robot by using the control device while checking the monitor, which displays the visual information from the visual sensors. To operate flexibly, expert operators who understand and are capable of training the remote-controlled robot well are required. Thus, operating a remote-controlled robot is difficult and includes the possibility of operational mistakes. This is because it is difficult for the operator to understand real environmental situations by using a monitor that only shows visual information. Therefore, for expert operation, numerous stages of training are required for the operator to recognize the surroundings from the visual information. Methods for improving the operability of the remote-controlled robot with respect to the mechanical design of the control device and the control method of the operation assist have been reported [24; 25]. This study focuses on the control method, because the control method can be adapted more easily to see improvements, as compared to varying the mechanical design of the control device for obtaining the same improved performance. To enhance the control method of the operation assist and thereby increase the operability of the remote-controlled robot, force and visual assists have been studied in particular. The force assist for the mobile robot has been widely researched to improve the operability and the safety performance. While operating a remote-controlled robot, force feedback is frequently employed to assist human operators in improving their perception of environments to assist their operation skills [26; 27; 28; 29; 30]. Meanwhile, visual assists for remote-controlled robots have been widely studied and used for real situations to improve the operability. For example, remote-controlled methods using visual assists have been studied using several types of sensors [31; 32; 33]. However, it is difficult to achieve safety performance by using only a visual assist [34; 35]. Hence, the evaluation of a combination method with force and visual assists is a meaningful study for remote-controlled methods. Therefore, force and visual assists of remote-controlled robots are proposed in this study to improve operability. This study proposes a remote-controlled method with force and visual assists to improve the operability and safety performance for a fully remote-controlled wheeled mobile robot. The force assist was generated to ensure the safety performance of the remote-controlled robot.