Kilian Baur

Online adaptive compensation of the ARMin Rehabilitation Robot

Robot-assisted arm therapy is increasingly applied in neurorehabilitation. The reason for this development over the last decades was that robots relieve the therapist from hard physical work while the training intensity can be increased. Importantly, an increase in training intensity is closely linked to functional improvements of the patient. However, usability of the robot for therapists was hardly considered an important factor in rehabilitation robot development so far. We believe that usability of the robot is a key factor for acceptance of the device by therapists. In this paper, an online adaptive compensation for the ARMin rehabilitation robot is presented, which aims at improving usability of the robot. Therefore, we expect ARMin therapy to become even more effective than conventional therapy at a level that is also relevant for the patient. Additionally, improved usability relieves the therapist from unnecessary/time-consuming tasks linked to robot handling. For the ARMin, the new online adaptive compensation takes over automatic updates of changed upper and lower arm lengths as well as adaptation of shoulder angle settings to fit the patients anthropometry. Simultaneously, the model-based compensation in ARMin is directly updated to account for hardware changes. Importantly, the online adaptive compensation provides improved performance of ARMin even at the borders of the workspace. In experiments, we could show that the adaptive online compensation relieves the force and position controller from additional burdens and increases the robot performance drastically especially at the workspace border.

Flowing to the Optimal Challenge: An Adaptive Challenge Framework for Multiplayer Games

Rehabilitation training is a key component in the treatment of patients with neurological disorders such as stroke and spinal cord injury. A key parameter in rehabilitation is to have a high level of intensity during training—that is, training where a patient performs a high number of repetitions under high levels of mental and physical effort. To address the need for increased intensity during training we propose the use of robotic devices to deliver training in multiplayer environments. Robotic devices have the potential to train multiple patients simultaneously under the supervision of a single therapist. However, when more than one patient is involved in training, for example during a competitive game, the differences in skill level become an important factor to consider. Here we discuss the implications of two-player competitive games for rehabilitation training. We focus our discussion in training for the upper extremity and frame our ideas in the context of the flow concept—from the field of psychology—and the challenge point framework—from the field of motor learning. We discuss how the introduction of an additional player, with different skill level, can affect these concepts and how we can use Dynamic Difficulty Adaptation methods to address possible issues. We hypothesize that multiplayer environments, with appropriate adjustments for difficulty, increase the intensity and motivation of training by expanding the flow zone of trainees.

Guidance in the nullspace reduces task difficulty in robot-assisted coordination training

Haptic guidance in robot-assisted therapy does not only relieve the therapist from physical work load and increase the possible training intensity. Haptic guidance can also be used to adapt the task difficulty level to the patients abilities, which is assumed to maximize the learning rate. Hereby, task difficulty can address either the patients physical ability (strength) or his/her coordination ability.

Performance-based viscous force field adaptation in upper limb strength training for stroke patients

Muscle weakness is one of the major deficits after stroke but specific strength training is seldom included in robot-assisted rehabilitation. At the same time, the emergence of robotic devices for stroke therapy offers technical possibilities for strength training. We propose a control strategy for strength training that is based on a viscous force field shaped towards the patients performance abilities at different positions and directions during a movement. The controller was implemented in the arm rehabilitation robot ARMin in combination with a one-degree-of-freedom repetitive tracking task. The viscous force field is adapted in each round as a function of the local performance profile (shape) and the performance sum of each round (task level). The patient gets feedback by visual representation of the tracking task displaying the position of the moving target object and the position of the patient cursor. We hypothesize that the performance-shaped task level of the viscous force field demands the maximum effort of the participant at each point of the trajectory. Furthermore, we hypothesize that the participants are more motivated by this controller for strength training than by controllers using a constant task level. The controller was tested in a feasibility study with 31 healthy subjects. The resulting individual task level of the viscous force field increased compared to the initial state but did not reach a steady state by (visual inspection). No differences in motivation compared to a controller using a constant viscous force field were identified. We propose the framework of differentiation in shape and task level of a viscous force field for difficulty adaptation in future rehabilitation games.

Missing depth cues in virtual reality limit performance and quality of three dimensional reaching movements

Background Goal-directed reaching for real-world objects by humans is enabled through visual depth cues. In virtual environments, the number and quality of available visual depth cues is limited, which may affect reaching performance and quality of reaching movements. Methods We assessed three-dimensional reaching movements in five experimental groups each with ten healthy volunteers. Three groups used a two-dimensional computer screen and two groups used a head-mounted display. The first screen group received the typically recreated visual depth cues, such as aerial and linear perspective, occlusion, shadows, and texture gradients. The second screen group received an abstract minimal rendering lacking those. The third screen group received the cues of the first screen group and absolute depth cues enabled by retinal image size of a known object, which realized with visual renderings of the handheld device and a ghost handheld at the target location. The two head-mounted display groups received the same virtually recreated visual depth cues as the second or the third screen group respectively. Additionally, they could rely on stereopsis and motion parallax due to head-movements. Results and conclusion All groups using the screen performed significantly worse than both groups using the head-mounted display in terms of completion time normalized by the straight-line distance to the target. Both groups using the head-mounted display achieved the optimal minimum in number of speed peaks and in hand path ratio, indicating that our subjects performed natural movements when using a head-mounted display. Virtually recreated visual depth cues had a minor impact on reaching performance. Only the screen group with rendered handhelds could outperform the other screen groups. Thus, if reaching performance in virtual environments is in the main scope of a study, we suggest applying a head-mounted display. Otherwise, when two-dimensional screens are used, achievable performance is likely limited by the reduced depth perception and not just by subjects’ motor skills.

Music meets robotics: a prospective randomized study on motivation during robot aided therapy

BackgroundRobots have been successfully applied in motor training during neurorehabilitation. As music is known to improve motor function and motivation in neurorehabilitation training, we aimed at integrating music creation into robotic-assisted motor therapy. We developed a virtual game-like environment with music for the arm therapy robot ARMin, containing four different motion training conditions: a condition promoting creativity (C+) and one not promoting creativity (C–), each in a condition with (V+) and without (V–) a visual display (i.e., a monitor). The visual display was presenting the game workspace but not contributing to the creative process itself. In all four conditions the therapy robot haptically displayed the game workspace. Our aim was to asses the effects of creativity and visual display on motivation.MethodsIn a prospective randomized single-center study, healthy participants were randomly assigned to play two of the four training conditions, either with (V+) or without visual display (V–). In the third round, the participants played a repetition of the preferred condition of the two first rounds, this time with a new V condition (i.e., with or without visual display). For each of the three rounds, motivation was measured with the Intrinsic Motivation Inventory (IMI) in the subscales interest/enjoyment, perceived choice, value/usefulness, and man-machine-relation. We recorded the actual training time, the time of free movement, and the velocity profile and administered a questionnaire to measure perceived training time and perceived effort. All measures were analysed using linear mixed models. Furthermore, we asked if the participants would like to receive the created music piece.ResultsSixteen healthy subjects (ten males, six females, mean age: 27.2 years, standard deviation: 4.1 years) with no known motor or cognitive deficit participated. Promotion of creativity (i.e., C+ instead of C–) significantly increased the IMI-item interest/enjoyment (p=0.001) and the IMI-item perceived choice (p=0.010). We found no significant effects in the IMI-items man-machine relation and value/usefulness. Conditions promoting creativity (with or without visual display) were preferred compared to the ones not promoting creativity. An interaction effect of promotion of creativity and omission of visual display was present for training time (p=0.013) and training intensity (p<0.001). No differences in relative perceived training time, perceived effort, and perceived value among the four training conditions were found.ConclusionsPromoting creativity in a visuo-audio-haptic or audio-haptic environment increases motivation in robot-assisted therapy. We demonstrated the feasibility of performing an audio-haptic music creation task and recommend to try the system on patients with neuromuscular disorders.Trial registrationClinicalTrials.gov, NCT02720341. Registered 25 March 2016, https://clinicaltrials.gov/ct2/show/NCT02720341

The “Beam-Me-In” Strategy Remote Haptic Therapist- Patient Interaction with Two Exoskeletons for Stroke Therapy

Background: We present a robot-assisted telerehabilitation system that allows for haptic interaction between therapist and patient over distance. It consists of two arm therapy robots. Attached to one robot the therapists can feel on their own arm the limitations of the patient’s arm which is attached to the other robot. Due to the exoskeleton structure of the robot, movements can be performed in the three-dimensional space. Methods: Fifteen physical and occupational therapists tested this strategy, named “Beam-Me-In”, while using an exoskeleton robot connected to a second exoskeleton robot in the same room used by the study experimenter. Furthermore, the therapists assessed the level of impairment of recorded and simulated arm movements. They quantified four typical impairments of stroke patients: reduced range of motion (active and passive), resistance to passive movement, a lack of ability to fractionate a movement, and disturbed quality of movement. Results: On a Likert Scale (0 to 5 points) therapists rated the “Beam-Me-In” strategy as a very useful medium (mode: 4 points) to evaluate a patient’s progress over time. The passive range of motion of the elbow joint was assessed with a mean absolute error of 4.9◦ (absolute precision error: 6.4◦). The active range of motion of the elbow was assessed with a mean absolute error of 4.9◦ (absolute precision error: 6.5◦). The resistance to passive movement (i.e. modified Tardieu Scale) and the lack of ability to fractionate a movement (i.e. quantification of pathological muscle synergies) was assessed with an inter-rater reliability of 0.930 and 0.948, respectively. Conclusions: The “Beam-Me-In” strategy is a promising approach to complement robot-assisted movement training. It can serve as a platform to assess and identify abnormal movement patterns in patients. This is the first application of remote three-dimensional haptic assessmen t applied to telerehabilitation. Furthermore, the “Beam-Me-In” strategy has a potential to overcome barriers for therapists regarding robot-assisted telerehabilitation.

Missing Depth Cues in Virtual Reality Decrease Performance of Three-Dimensional Reaching Movements

Goal-directed reaching movements in three-dimensions are important for our interaction with the environment. Instrumented setups displaying virtual targets for rehabilitation training of reaching movements often provide limited depth cues, which may affect movements. This work aims to quantify effects of limited depth cues on reaching movements. We developed a virtual environment for assessing three-dimensional reaching movements that allows different depth cues to be enabled or disabled. By imposing a fixed spatial tolerance around targets for speed-accuracy trade-off, completion time normalized with the straight-line distance to the target was used to measure reaching performance. In the present study, 8 (control) subjects using a typical monitor setup applied in rehabilitation were compared to 7 subjects using a head-mounted display and receiving additional depth cues, namely, hard-referenced objects of known size, motion parallax due to tracked head-movements, and stereopsis. Control subjects required on average 9.88 s/m straight-line distance, while subjects using the head-mounted display required only 3.15 s/m straight-line distance. Additionally, movement trajectories of control subjects showed a different pattern, indicating a lack of reliable depth information. Thus, state-of-the-art rehabilitation setups are challenging already for healthy subjects. This challenge can be reduced by improving the provided visual depth cues.