Although passing static obstacles is a classic problem in robot navigation, the num- ber of studies conducted for side-by-side walking modes is still limited. When en- countering situations where it is necessary to pass static obstacles, the current solutions are still facing many shortcomings, lacking a plan to allow a side-by-side wheelchair to pass obstacles in a natural way as humans do. For example, assume that a caregiver escorts an elderly person as they stroll around a mall. Because the caregiver is mainly responsible for the walk, we call him the leader. And be- cause the elderly follows the caregiver from place to place, we call him the follower. During the walk, they encounter an obstacle in the middle of the pathway as illus- trated in Figure 4-2, and they need to pass the obstacle. The leader, who in this situation is on the left of the pair, decides to pass the obstacle to the left. We can see that the follower may have two solutions (a,b) (Figure 4-3) for choosing to pass
the obstacle. In the case (a), called Standard mode, the follower decides to keep a rigid connection with the caregiver and he tries to not allow the obstacle to interfere with their relationship, therefore he moves to the same side of the obstacle as the leader, i.e. he moves to the left of the obstacle. On the other hand, in case (b), the follower considers that it would be better if he moves to the other side of the obstacle with the leader, i.e. he decides to move to the right side of the obstacle.
Figure 4-2: An obstacle passing situation of a pair in a mall
Based on our observation of people walking in pairs, in some cases, pairs usu- ally choose mode (a) (Standard mode) for passing, yet in some other cases, they select mode (b). From this observation, we believe that people do not choose a random passing mode among two modes (a) and (b) but focus on one for some reasons. The reasons here should be related to their optimal comfort in walking. As mentioned in the previous chapters, for the purpose of developing the naviga- tion function for side-by-side robotic wheelchairs, the navigation function should be able to generate a decision which is similar to humans in walking, i.e. the naviga- tion function should be able to choose the correct passing mode (a) or (b) for each particular situation.
So far, researchers have proposed and developed several possible solutions for dealing with passing static obstacles problem in side-by-side walking mode.
However they still have some limitations.
Based on the Kinpara et al.’s solution [8], the robot always selects mode (a) and changes its relative position with the caregiver from alongside to behind for passing (Figure 4-3(a)). Although this solution is useful in some cases, it is oversimplified in other cases when we can see that pairs normally choose mode (b) for passing. As can be seen, the Kinpara et al.’s solution has no mechanism to decide between two modes (a) and (b).
Another solution came from Morales et al. [12]. By incorporating eight factors related to humans’ comfort in side-by-side walking mode, including velocities, ac- celerations, distance to obstacles, etc., their model can maintain a better relation- ship with the caregiver, i.e. the model can optimize the comfort of both members of the pair in passing static obstacles. Yet this solution is developed for the situa- tion in which there is an obstacle placed next to a wall. Essentially this changes the width and direction of the pathway, therefore the solution becomes uncertain in this situation. As a result, their robot was not developed to decide that which of the two modes (a,b) will bring better comfort for both the caregiver and the wheelchair user.
If we consider that being stationary is a particular state of moving obstacles, then a solution of Ferrer et al. [10] can be considered. Based on social-force and proxemics concepts, they developed a mobile robot to accompany a person in a crowded environment. The robot tries to maintain a comfortable distance between the robot, its companion, and surrounding people. Yet if we put their model into this situation, the model does not have any mechanism for choosing mode (a) or mode (b).
In the work presented here, based on Morales et al.’s model, I developed a new model to help the side-by-side robotic wheelchairs to overcome these limitations, i.e the robot is able to decide the mode that it should take for passing the obstacle in the middle of a pathway by imitating the human decision making process, es- pecially focusing on walking sessions of a caregiver and a disabled person/patient sitting on a wheelchair. The mission is accomplished by adding Vision factor, a
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(a) Kinpara, Kobayashi et al
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(c) Observed behavior
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(b) Moracles et al
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(d) Illustration
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(a) Kinpara, Kobayashi et al
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(c) Observed behavior
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(b) Moracles et al
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(b)Figure 4-3: Obstacle (𝑂) passing by a caregiver (Leader = 𝐿) and a robotic wheelchair (Follower = 𝐹 ).
new factor discovered in the study that affects the process in this situation. This study has been presented in [33].
The study presented in Sections 4.2 and 4.3 includes three stages: (1) data collection that includes a user study, (2) developing a model based on collected data, and (3) model validation through simulations. Section 4.4 will summarize the main results and limitation of the work.