INTRODUCTION:Studies in robotic therapy which applied the performance enhancement approach report improvements in motor performance during training, though these improvements do not always transfer to motor learning. OBJECTIVES:We postulate that there exists an assistance threshold for which performance saturates. Above this threshold, the robot's input outweighs the patient's input and likely learning is not fostered. This study investigated the relationship between assistance and performance changes in stroke patients to find the assistance threshold for performance saturation. METHODS:Twelve subacute and chronic stroke patients engaged in five sessions (over two weeks, each 60 min) in which they performed a reaching task with the rehabilitation robot H-Man in presence of varying levels of haptic assistance (50 N/m to 290 N/m, randomized order). In two additional sessions, a therapist manually tuned the assistance to promote maximal motor learning. RESULTS:Higher levels of assistance resulted in smoother and faster performance that saturated at assistance levels with K ≥ 110 N/m. Also, the therapist selected assistance levels of K = 175 N/m or below. CONCLUSION:The findings of the study indicate that low levels of assistance (K ≤ 175 N/m) can sufficiently induce a significant change in performance.

Technology aided measures offer a sensitive, accurate and time-efficient approach for the assessment of sensorimotor function after neurological insult compared to standard clinical assessments. This study investigated the sensitivity of robotic measures to capture differences in planar reaching movements as a function of neurological status (stroke, healthy), direction (front, ipsilateral, contralateral), movement segment (outbound, inbound), and time (baseline, post-training, 2-week follow-up) using a planar, two-degrees of freedom, robotic-manipulator (H-Man). Twelve chronic stroke (age: 55 ± 10.0 years, 5 female, 7 male, time since stroke: 11.2 ± 6.0 months) and nine aged-matched healthy participants (age: 53 ± 4.3 years, 5 female, 4 male) participated in this study. Both healthy and stroke participants performed planar reaching movements in contralateral, ipsilateral and front directions with the H-Man, and the robotic measures, spectral arc length (SAL), normalized time to peak velocities (TpeakN ), and root-mean square error (RMSE) were evaluated. Healthy participants went through a one-off session of assessment to investigate the baseline. Stroke participants completed a 2-week intensive robotic training plus standard arm therapy (8 × 90 min sessions). Motor function for stroke participants was evaluated prior to training (baseline, week-0), immediately following training (post-training, week-2), and 2-weeks after training (follow-up, week-4) using robotic assessment and the clinical measures Fugl-Meyer Assessment (FMA), Activity-Research-Arm Test (ARAT), and grip-strength. Robotic assessments were able to capture differences due to neurological status, movement direction, and movement segment. Movements performed by stroke participants were less-smooth, featured longer TpeakN , and larger RMSE values, compared to healthy controls. Significant movement direction differences were observed, with improved reaching performance for the front, compared to ipsilateral and contralateral movement directions. There were group differences depending on movement segment. Outbound reaching movements were smoother and featured longer TpeakN values than inbound movements for control participants, whereas SAL, TpeakN , and RMSE values were similar regardless of movement segment for stroke patients. Significant change in performance was observed between initial and post-assessments using H-Man in stroke participants, compared to conventional scales which showed no significant difference. Results of the study indicate the potential of H-Man as a sensitive tool for tracking changes in performance compared to ordinal scales (i.e., FM, ARAT).

This paper analyses the dynamics of cable-driven robots with a passive backbone and develops techniques for their dynamic identification, which are tested on the H-Man, a planar cabled differential transmission robot for haptic interaction. The mechanism is optimized for human–robot interaction by accounting for the cost-benefit-ratio of the system, specifically by eliminating the necessity of an external force sensor to reduce the overall cost. As a consequence, this requires an effective dynamic model for accurate force feedback applications which include friction behavior in the system. We first consider the significance of friction in both the actuator and backbone spaces. Subsequently, we study the required complexity of the stiction model for the application. Different models representing different levels of complexity are investigated, ranging from the conventional approach of Coulomb to an advanced model which includes hysteresis. The results demonstrate each model's ability to capture the dynamic behavior of the system. In general, it is concluded that there is a trade-off between model accuracy and the model cost.

the aging population and an increase in the demand for post injury therapy has generated particular interest in technology based solutions for neurorehabilitation. This paper presents a practice based approach for teaching design of technology for post-injury training of motor-functions. The content of the course and its implementation using designed 2DOF planar robot are discussed here.

Haptic force fields are widely used in studies on motor adaptation, motor retention, and motor recovery in both healthy and impaired subjects. In the main paradigm the hand is guided or perturbed along specific paths or channels in order to investigate different aspects underlying the human motor control. Programming such fields for complex haptic environments can be very challenging and is often not feasible for clinicians and therapists. The aim of this paper is to introduce a more intuitive and clinician-friendly programming method capable of transforming a 2D drawing (stored as an image) into a haptic environment or planar force field. By considering the image intensity as a position-dependent potential field, the energy function is approximated through locally weighted projection regression (LWPR). Robot forces are then computed through the gradient of the regressed potential. The proposed method is validated with a two degrees-of-freedom planar manipulandum, the H-Man, and a preliminary shape recognition experiment involving blindfolded healthy subjects.

Current robotic rehabilitation devices have a high cost-to-benefit ratio, which prevents their large scale adoption by the clinical rehabilitation community. This paper first presents H-Man, a low cost planar robot, as a quantitative assessment and training tool. This is followed by a preliminary study to investigate baseline performance measures for motor assessment during reaching tasks as a step toward replacing conventional ordinal scales with continuous quantitative scales. Thirteen healthy and one participant with upper limb motor impairment participated in the study and performed reaching tasks with their dominant and non-dominant hands in three directions. The results from healthy subjects indicate no significant difference between different directions for both limbs and also between corresponding directions of dominant and non-dominant limbs (p > 0.05, all cases). However, differences in measures can be observed for the impaired subject.

Conventional assessment of sensorimotor functions is carried out using standard clinical scales which are subjective and insufficiently sensitive to changes in motor performance. Alternatively, sensor based systems offer a quantitative approach to motor assessment. We have designed a set of low cost, easy to use instrumented objects to assess a subject's performance during skilled tasks. In this pilot study we discuss the design of one object, the intelligent key, and describe how it can be used to assess a subject's performance during fine manipulation tasks using the proposed metrics and techniques. Three subjects with motor disability and one healthy subject participated in this study. Subjects performed insertion and rotation tasks that mimic the skills used in day to day key manipulation. A threshold detector algorithm based on Teager Energy Operator was applied to the object acceleration signal to quantify time spent struggling with the task and Spectral Arc Length was used to assess the smoothness of pronation/supination. Overall, the results indicate that increased difficulty in task performance correlates with decreased smoothness in task performance.

This paper presents the results of a preliminary assessment study to investigate baseline performance measures and differences between control and stroke participants during reaching tasks in three directions. H-Man, planar robot is, used for this purpose. Thirteen healthy and two chronic stroke patients with upper limb motor impairment participated in the study. Assessment of performance was made through three task parameters (smoothness of movement, peak velocity, and time to peak velocity). The results from healthy subjects indicate no significant difference between different directions, however significant differences are observed in stroke participants across different directions for smoothness measure (Spectral Arc Length). All the three measures show significant differences between control and Stroke participants for corresponding directions.

Purpose– The purpose of this paper is to propose a method to avoid hyperstaticity and eventually reduce the magnitude of undesired force/torques. The authors also study the influence of hyperstaticity on human motor control during a redundant task.Design/methodology/approach– Increasing the level of transparency of robotic interfaces is critical to haptic investigations and applications. This issue is particularly important to robotic structures that mimic the human counterpart's morphology and attach directly to the limb. Problems arise for complex joints such as the wrist, which cannot be accurately matched with a traditional mechanical joint. In such cases, mechanical differences between human and robotic joint cause hyperstaticity (i.e. over-constrained) which, coupled with kinematic misalignment, leads to uncontrolled force/torque at the joint. This paper focusses on the prono-supination (PS) degree of freedom of the forearm. The overall force and torque in the wrist PS rotation is quantified by means of a wrist robot.Findings– A practical solution to avoid hyperstaticity and reduce the level of undesired force/torque in the wrist is presented. This technique is shown to reduce 75 percent of the force and 68 percent of the torque. It is also shown an over-constrained mechanism could alter human motor strategies.Practical implications– The presented solution could be taken into account in the early phase of design of robots. It could also be applied to modify the fixation points of commercial robots in order to reduce the magnitude of reaction forces and avoid changes in motor strategy during the robotic therapy.Originality/value– In this paper for the first time the authors study the effect of hyperstaticity on both reaction forces and human motor strategies.

This work investigates how to design a comfortable wrist exoskeleton which complies with the natural coordination mechanisms in the redundant wrist. Human sensorimotor control is known to impose intrinsic kinematic constraints to solve redundant motor tasks. To this end, the effect of an exoskeleton on natural motor strategies was assessed during pointing tasks performed with the wrist. The exoskeleton was designed based on the kinematic model of one specific subject. Then wrist orientation was observed during pointing tasks with the exoskeleton in the following conditions: i) optimal alignment between human and exoskeleton joints; ii) varying degrees of misalignment between human and exoskeleton joints; iii) optimal alignment while the PS axis was locked (i.e. no redundancy). The results exhibited a modification of the natural coordination mechanisms characterized by a subject-specific Koenderink shape index. Kruskal-Wallis pairwise analyses demonstrated a significant variation between test conditions indicating a change of intrinsic constraints with misalignment and locked PS. The assessment methodologies presented in this paper can be used to test for ergonomic constraints and can guide the design of robotic systems performing kinematically redundant tasks.

Increasing the level of transparency in rehabilitation devices has been one of the main goals in robot-aided neurorehabilitation for the past two decades. This issue is particularly important to robotic structures that mimic the human counterpart's morphology and attach directly to the limb. Problems arise for complex joints such as the human wrist, which cannot be accurately matched with a traditional mechanical joint. In such cases, mechanical differences between human and robotic joint cause hyperstaticity (i.e. overconstraint) which, coupled with kinematic misalignments, leads to uncontrolled force/torque at the joint. This paper focuses on the prono-supination (PS) degree of freedom of the forearm. The overall force and torque in the wrist PS rotation is quantified by means of a wrist robot. A practical solution to avoid hyperstaticity and reduce the level of undesired force/torque in the wrist is presented, which is shown to reduce 75% of the force and 68% of the torque.

This paper analyzes the accuracy of non-invasive methods to determine subject-specific kinematics of wrist axes based on unrestricted measurements. Adapting methods from the literature, joint parameters are fitted from measurements derived through an in-vivo, non-invasive procedure. This paper analyzes the accuracy of these fitting methods using a mechanical mock-up, with known geometry and kinematic structure similar to the human wrist, which provides a ground truth for assessment of accuracy. Numerical simulations show that while the range of motion affects the accuracy of parameter estimation, the relative error in the parameters is below 4% for range of motions above 20%. The method was used to fit measurements performed on a human subject and resulting parameters were applied in the design of a subject-specific, ergonomic exoskeleton, which did not significantly alter the natural motor strategies of the subject during a pointing task.