Krzysztof Kędzior

Designing and optimization of parameters of delta-4 parallel manipulator for a given workspace

In the paper, the algorithm of designing some geometrical parameters of a Delta parallel manipulator has been described. The manipulator is to work in a specified workspace, which is given as a set of points. The first step of the algorithm seeks the possible solutions, and because there are an infinite number of them, the objective of the second step is to limit the number by an optimization. Owing to this, it is possible to find parameters of the manipulator, whose workspace contains the specified points.

Methodology of off-line software compensation for errors in the machining process on the CNC machine tool

Abstract Off-line software machining accuracy enhancement has been suggested based on the prediction of the machining error Δ → =[ Δ x , Δ y , Δ z ] . It has been assumed that errors in the machine tool workspace can be analysed as a superposition of the components Δ → g , Δ → m , Δ → n where Δ → g results from the geometric surface description, Δ → m results from the limited machine tool stiffness and Δ → n results from the cutting tool deflection during machining. Geometric description error Δ → g =[ Δ xg , Δ yg , Δ zg ] arises from the surface geometric modelling phase in the CAD system. The NURBS (Non-Uniform Rational B-Spline) technique has been selected as the most effective for the complex shape surface description, supported by the least square principle. Then the distances between the measuring points and the calculated points on the described surface patch have been determined and a function representing the inaccuracy of the surface description has been defined. The Δ → m =[ Δ xm , Δ ym , Δ zm ] error has been calculated based on periodic measurements of the machine tool positions while applying static forces to the spindle endpoint. The points in the factor have been selected according to principles of mathematical experiment planning. The polynomial regression-based relationships have been derived for Δ → m error description. The results have been validated using statistical correlation analysis. A similar approach has been adopted for the estimation of the cutting tool deflection error Δ → n =[ Δ xn , Δ yn , Δ zn ] . The resulting Δx, Δy and Δz components have been introduced as compensation values adding up to the regular tool movements along the programmed tool path. A special postprocessing program has been developed for doing this job, herein called active task in order to differentiate it from standard postprocessing functions named as passive tasks.

Modeling of Muscle Action and Stability of the Human Spine

Biomechanical investigations of the human spine are nowadays rarely taken up for purely cognitive reasons. Usually they are stimulated by needs of various areas of contemporary civilization and directed toward applying their results in medicine (etiology of diseases and defects of the spine, rehabilitation, occupational medicine), technology (e.g. influence of a vehicle upon the spine of its human operator in normal or emergency conditions), and sports (influence of overloads due to sport training upon the spine).

Design of parameters of parallel manipulators for a specified workspace

In this paper an algorithm for designing spatial parallel manipulator parameters for a given workspace has been presented. At the beginning, architecture has been chosen that describes a general parallel manipulator. The manipulator may possess any number of limbs, consisting of links connected by spherical, revolute or linear joints as well as actuators. The parameters, which will be determined, are the lengths of the links of kinematic chains, the coordinates of the fixing points of the chains to the platform and the base, and orientations of the revolute engines axes situated at the base. The workspace may be specified in the form of any shape in the space containing a set of points of known coordinates and the limits in which the geometrical parameters may vary. The algorithm does not determine the exact values of the parameters, but only their functions. It leads to the necessity for further research in order to optimise the solutions.

The potential role of brain asymmetry in the development of adolescent idiopathic scoliosis: a hypothesis.

BACKGROUND The size asymmetry of cerebral hemispheres may predispose to head tilt and asymmetric blocking of the zygapophysial joints, potentially leading to the development of compensatory curvatures in the lower segments of the spine. OBJECTIVE To analyze the effects of spinal manipulation, maintained by an exercise program, on the progression of idiopathic adolescent scoliosis in 2 children aged 6 and 10. CLINICAL FEATURE The scoliosis found was 16 and 60 degrees. INTERVENTION AND OUTCOME For diagnosis and monitoring of therapy, we recorded qualitative parameters of shoulder asymmetry, axillary line asymmetry, and scapular angle position. Manual treatment consisted of the examinations of all sliding motion in zygapophysial joints and both sacroiliac joints and removing the limitations of the sliding motions according to the method of Karel Lewit. The treatment procedure consisted of 3 or 4 manipulations within 17 months and an exercise program. The manipulation effects were maintained by the exercise program. The exercises were done in 2 or 3 sessions weekly for a year. In both patients we observed that scoliosis decompensation was successfully stopped and the effects of the correction persisted for 10 years. CONCLUSION Brain and head asymmetry may be only a transient state, predisposing to asymmetric blocking at the atlanto-occipital level. Removal of blocking may prevent curve progression in children who had adolescent idiopathic scoliosis. The manipulative therapy may also have a promising effect on retarding curve progression when used in skeletally immature patient.

Determination of parameters of 3-dof spatial orientation manipulators for a specified workspace

The objective of the paper is to present a method of designing geometrical parameters of 3-dof orientation mechanisms. The parameters are to be determined for a given workspace, which in this case is described as a set of angles of orientation. An algorithm is presented, based on the equations of constraints which makes it possible to obtain the parameters of a manipulator. whose workspace involves the specified taskspace.

Identification and geometrical modelling of complex shape surfaces using coordinate measuring machine and CAD/CAM systems

Abstract Two similar methods for the geometric identification of complex shape surfaces using the scanning measurement technique on a coordinate measuring machine (CMM) will be presented in this work. The first method employs the surfaces defined by the CAD system parametric technique based on the set of measurement points. The coordinates of points in space are determined by measurement in successive scanning planes with a given measuring step. The second method employs the surfaces defined by the analytically generated orthogonal curve meshes given by Newtons interpolation function. The interpolation points are the measurement points in the Cartesian space for a given measuring step. The generation technique of the interpolation function is then applied by using the interpolation method to define the arbitrary coordinate point set of the range of the measured net. Following this method of identification, some corrective procedure for measuring the results of surface coordinate points are proposed. These correction procedures result from use of the probe end in the coordinate technique. As a consequence of the presented corrective procedures, the authors propose useful software (numerical programmes) for the applied CMM during measuring of the complex shape surfaces. In the final part of the work, the sets of points obtained from these measurements are used to the develop 3D geometrical models of surfaces in the CAD system. The discussed techniques of identification and modelling are adopted in the design of a TV tube and the shape surface of the radial bone in bioengineering as practical examples.

Musculoskeletal Load Assessment of the Upper Limb Positions Subjectively Chosen as the Most Convenient

Work posture is determined by interdependence between work stand design, the necessity to perform given activities, and the anthropometric dimensions of the worker, but it also depends on individual preferences. The aim of the study was to compare the musculoskeletal load of the right upper extremity under conditions of imposed (standard) upper limb position and subjectively chosen ones, and to assess the influence of the changes in magnitude of the external force on the musculoskeletal load in the examined limb positions. Ten healthy male participants took part in the study. Muscular load associated with different upper extremity positions with and without external load were assessed. Musculoskeletal load for standard and subjectively chosen limb positions and two different values of external load were compared by means of theoretical and experimental methods. Results indicate that differences in musculoskeletal load between imposed and subjectively chosen limb positions were not high enough to show statistically significant differences, and the upper limb position chosen by the participant does not always cause the lowest musculoskeletal load.

Non-Linear Finite Element Analysis of Formation and Treatment of Intervertebral Disc Herniae

A biomechanical model of the spine motion segment L2/L3 consisting of the truncated vertebrae, endplates, intervertebral disc and pieces of anterior and posterior longitudinal ligaments has been used for a computer simulation study. A non-linear finite element analysis has shown that small loads compressing the spine, not greater than those occurring in everyday life, cause loss of stability of an intervertebral disc, resulting in lateral dislocation of its nucleus pulposus. This could be a potential cause of discopathy. The model indicates that conservative therapy of herniated disc by the traction method may result in retraction of hernia by about 40 per cent.

Computerized Method for Work Space Optimization in Conditions of Static Work

The aim of this research was to develop a theoretical method for the ergonomic optimization of the work space of the upper limb. This method is based on a model of the upper extremity with 7 degrees of freedom. It consists of 3 rigid elements modeling the arm, forearm, and hand and 34 upper extremity muscles. The trunk is considered immobile. The shoulder joint is modeled as a rotating kinematics pair of third class, the elbow and wrist joints--of fourth class. The minimum sum of muscle force moments in the joints and soft saturation muscle cooperation criterion were used as merit criteria. The developed method makes it possible to effectively solve, in a defined work space, the task of work space optimization.