Modelling of the human shoulder as a parallel mechanism without constraints

Abstract

The synthesis of shoulder kinematics, either for simulation in a model or imitation in a robot, is a challenging task because of the contact between shoulder blade and ribcage. As the shoulder moves, the shoulder blade glides over the ribcage. In kinematic models used to predict musculoskeletal kinetics, the contact is included using equality constraints, creating interdependencies between the kinematic coordinates. Such interdependencies make motion planning complex. Robotic mechanisms often imitate the shoulder's end-effector kinematics but not the gliding shoulder blade architecture It is only recently that a gliding shoulder blade architecture has been mechanically achieved. The goal of this paper is to propose a novel kinematic parallel model of the shoulder that includes the contact without using constraints. Mechanically, the gliding architecture is replaced with a parallel architecture. A shoulder model with constraints is used to build the parallel model. It is shown that replacing the contact constraints with kinematically equivalent kinematic chains, leads to a 2-3 parallel platform model of the shoulder. The scaffold model and parallel model parameterisations of the shoulder's kinematics are analysed in terms of the forward kinematic map. The coordinate spaces of the kinematic maps are analysed, resulting in three minimal parameterisations. Each minimal parameterisation uses a set of coordinates equal to the number of degrees of freedom. The minimal coordinates are independent and considerably simplify motion planning.

Kinematic models of the upper limb joints for multibody kinematics optimisation: An overview

“…The scapulothoracic joint is commonly described as a contact between a cone or an ellipsoid representing the thorax and different points of the scapula. Recently, an equivalent but simpler mechanism made of two universal and two prismatic joints was proposed (Ingram et al, 2016). Finally, another way to integrate the interdependency between shoulder girdle DoFs is to introduce scapular and clavicular rhythm equations as a function of the humeral angles (de Groot and Brand, 2001).…”

“…Furthermore, this method can lead to non-physiological interpenetrations of the scapula into the thorax. Solutions to this problem have been proposed in the literature by imposing the scapula plane to be tangential to different geometries representing the thorax (Naaim et al, 2015;Tondu, 2007) or by introducing an equivalent parallel mechanism made of universal and prismatic joints (Ingram et al, 2016) that may be simpler to implement than the gliding conditions. These last models have the advantages of being easily customisable to patients.…”

Effects of glenoid inclination and acromion index on humeral head translation and glenoid articular cartilage strain

“…2, A). 19,36 The model was developed from magnetic resonance imaging (MRI) scans of a 27-year-old healthy male volunteer showing no signs of glenohumeral, acromioclavicular, or sternoclavicular joint disorders. MRI scans were obtained using a specific protocol consisting of two 3-dimensional T1-weighted sequences on a 3-T MRI scanner (Trio; Siemens Healthcare, Wuppertal, Germany).…”

“…The undetermined problem of muscle force coordination was solved using an inverse dynamics approach followed by a nullspace optimization. 11,[18][19][20]36 A glenohumeral joint stability criterion based on a cost function was included to maintain the joint force away from the subluxation limit. The arm weight was estimated at 37.5 N (5% of volunteer's weight), applied at 320 mm from the joint center along the humeral axis.…”

Modelling of the human shoulder girdle as a 6-4 parallel mechanism with a moving scapulothoracic joint

“…To date, only a few musculoskeletal models for the shoulder and upper limb have been developed that are most commonly used for a variety of purposes [1]: Swedish Shoulder Model [2,3], Delft shoulder and elbow model (DSEM) [4,5], Newcastle shoulder model (NSM) [6], Holzbaur's upper extremity model (HM) [7], Anybody model [8], Garner's model [9] and Dickerson's model [10]. Owing to the increasing interest of researchers in kinematic properties of the human shoulder, a number of different shoulder models based on open-loop [11][12][13][14][15] and closed-loop kinematic chains [14,[16][17][18][19][20][21] have been developed. Characteristically, the open-loop chain shoulder models have rather basic structures which simplify the kinematic and dynamic analyses.…”