Physical interaction between humans and robots in a remote environment can be realized safely with bilateral teleoperation. The acceleration-based scaling bilateral controller and the reaction force estimator implemented with the disturbance observer facilitate robust control and vivid touch sensation between different structures. This paper introduces a replica-side security enhancement method when the operator applies excessive force on the master during scaling bilateral motion. Initially, the system follows four-channel acceleration-based scaling bilateral control. It switches to the master side virtual impedance controller and replica side force controller as the bearable force limit is reached on the replica. As a result, the operator-applied excessive force is not transmitted to the remote end, and the master maneuvers freely following the operator's intention. This method supports the operator's freedom while protecting the replica object. This study derives the value of virtual impedance aiming at high reproducibility. As a result, the operator receives replica side object impedance throughout the operation even when controllers are switched. This study analyzes the stability considering pole placement with system parameter variations. Experiments verified the proposed method. The results demonstrate that the proposed method ensures the safety of remote objects while the operator freely applies excessive force. The operator was able to successfully sense object impedance irrespective of whether the system followed scaling bilateral control or constrained scaling motion control.

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