Table 2 Features of modalities of human robot interaction and their implementation in robot-mediated therapy

Passive,

passive-mirrored

The device is programmed to follow a desired trajectory/force profile with a strong attractor (up to 1000 N/m) towards it.

In the case of passive mirrored, the desired input is given by the subject with the unimpaired hand. In some cases, these trajectories can be set by the therapist during a “learning” phase.

Moving attractor

In such a case the assistance is lower than in passive control, the robot is still attracted towards a minimum jerk or smooth trajectory but the amount of assistance can be modulated by varying the stiffness that attracts the robot to the trajectory.

Triggered assistance

The subject initiates a movement without assistance. The robot observes that the on-going performance if the task is not completed (e.g. time expired) and intervenes taking the full control, as in the passive mode.

Assistive constant force

Force oriented towards the target or weight support when movement is against gravity.

EMG-proportional

The power of the EMG signal is used to control the actuators.

Pushing force (in case of delay)

A force aligned with the movement direction assists the subject only if there is a delay in comparison with a scheduled motion pattern.

Spring-damper guidance

Elastic or visco-elastic force fields aim at reducing the lateral displacement from a desired trajectory.

Tunnels

These can be displaced within the virtual environment to produce a haptic feedback only if error overcomes a (large) threshold value. A tunnel can be seen like a lateral spring-damper system plus a dead band zone which makes the haptic intervention discrete in time. This particular cueing of errors relates to a corrective strategy.

Spring against movement

The device opposes movements through an elastic force-field pulling back to the start position.

Damper against movement

The device generates a force opposing the movement based on current velocity. Although this increases the effort of the subject, it also stabilizes the movement by damping oscillations.

Not clear

The information in the text (or its references) did not allow classifying the article. As an instance, if the only mention to the physical interaction was “the robot assisted the subjects during the task”, this was considered not clear due to not providing details on the method of assistance.