PubMed · 12033054
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
Anthony G Borschneck, Charles Spotts. 2002. Traction force challenge.. https://pubmed.ncbi.nlm.nih.gov/12033054/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
The statics and dynamics of pneumatic power screwdriver operation were investigated in the context of predicting forces acting against the human operator. A static force model is described in the paper, based on tool geometry, mass, orientation in space, feed force, torque build up, and stall torque. Three common power hand tool shapes are considered, including pistol grip, right angle, and in-line. The static model estimates handle force needed to support a power nutrunner when it acts against the tightened fastener with a constant torque. A system of equations for static force and moment equilibrium conditions are established, and the resultant handle force (resolved in orthogonal directions) is calculated in matrix form. A dynamic model is formulated to describe pneumatic motor torque build-up characteristics dependent on threaded fastener joint hardness. Six pneumatic tools were tested to validate the deterministic model. The average torque prediction error was 6.6% (SD = 5.4%) and the average handle force prediction error was 6.7% (SD = 6.4%) for a medium-soft threaded fastener joint. The average torque prediction error was 5.2% (SD = 5.3%) and the average handle force prediction error was 3.6% (SD = 3.2%) for a hard threaded fastener joint. Use of these equations for estimating handle forces based on passive mechanical elements representing the human operator is also described. These models together should be useful for considering tool handle force in the selection and design of power screwdrivers, particularly for minimizing handle forces in the prevention of injuries and work related musculoskeletal disorders.
Several grafts and several fixation techniques have been introduced for PCL reconstruction over the past years. To date, autograft and allograft tissues are recommended for PCL reconstruction, whilst synthetic grafts should be avoided. Autograft tissues include the bone-patellar tendon-bone graft, the hamstrings and the quadriceps tendon. Allograft tissues are increasingly being used for primary PCL reconstruction. The use of allograft tissues requires a number of formal prerequisites to be fulfilled. Besides the previous mentioned graft types allograft tissues include Achilles and tibialis anterior/posterior tendons. To date no superior graft type has been identified. Several techniques and devices have been used for fixation of a PCL replacement graft. Most of these were originally developed for ACL reconstruction and then adapted to PCL reconstruction. However, biomechanical requirements of the PCL differ substantially from those of the ACL. To date, requirements for PCL graft fixations are not known. From a systematic approach femoral graft fixation can either be achieved within the bone tunnel (nearly anatomic) with an interference screw or outside the bone tunnel on the medial femoral condyle using a staple, an endobutton or a screw. Tibial graft fixation can be achieved either with an interference screw in the bone tunnel or with a staple, screw/washer or sutures tied over a bone bridge outside the bone tunnel (extra-anatomic). An alternative fixation on the tibial side is the inlay technique that reduces the acute angulation of the graft at the posterior aspect of the tibia. Further research is necessary to identify the differences between the various fixation techniques.
Gradually it is getting clear that motor development - in particular balance control - in so-called "low-risk" preterm infants often differs from that in full-term infants. However, little is known on the etiology and pathophysiology of these problems. The aim of this study was to evaluate postural behavior during reaching by means of kinetic and kinematic measurements. Preterm infants (n = 32) without cerebral palsy were investigated longitudinally at the corrected ages of 4 and 6 mo. Thirteen age-matched full-term infants served as controls. Cognitive and motor development were assessed by means of the quality of General Movements (GMs) at 4 mo and Bayley scales at 6 and 12 mo. The infants were lying supine on a forceplate reaching for a toy and the kinetics of the total body's Center of Pressure (COP) was measured in cranial-caudal and medial-lateral direction. The analysis focused on COP displacement, Vmax and oscillatory changes of the COP displacement during reaching. The kinematic analysis of reaching focused on movement units, Vmax and a compound kinematic variable reflecting the quality of reaching. The results showed that preterm infants showed a remarkable "still" postural behavior, which differed significantly from the mobile COP behavior of the full-term infants. More "still" postural behavior at 6 mo was associated with a better quality of reaching movements and with normal GMs at 4 mo. We concluded that "still" postural behavior is an adequate postural strategy of preterm infants. But it might be that this postural behavior is an indicator of later dysfunction.