This paper proposes a mode switching bilateral control for the extension of motion areas. Conventionally, a bilateral control with a dynamical matrix has been used to achieve haptic transmission with different motion ranges between the master and slave systems. However, this approach still does not allow operators to enhance operability, especially when the slave system is in contact with environment. Taking the contact motion in the bilateral control into consideration, a basic bilateral control with an Hadamard matrix for the same motion areas is suitable for immediate and fine haptic transmission. To solve the contact motion problem, the proposed control structure switches the dynamical and the Hadamard matrices between free and contact motion. The characteristic of the proposed method is that the structure of the disturbance observer is applied to the modal space in order to solve the initial-value problem. With this method, smooth switching of the modal transformation matrix is achieved in both soft and hard environments. As a result, the operability of the different motion areas will be enhanced.
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