Dual Screw Research Articles

The treatment of femoral neck fractures: results using cephalocervical screws with sliding mechanism

A new device for the treatment of femoral neck fractures that uses 2 cephalocervical screws in a sliding mechanism allowing linear intraoperative and postoperative compression has been developed. The purpose of this retrospective study was to determine the results using this device for the treatment of stable and unstable femoral neck fractures. Between November 2007 and November 2011, 61 consecutive skeletally mature patients with femoral neck fractures were treated with a new cephalocervical screw (Dual SC screw; KISCO DIR Co., Ltd., Kobe). All contactable patients were followed up for a minimum of 16 weeks postoperatively (range 16-123 weeks). Clinical and radiographic examinations were performed at the final evaluation. Healing and return to activities of daily living were used to evaluate outcomes. There were 51 women and 10 men with a mean age of 80.8 years (range, 41-99). The average of surgical time was 33.1 min (21-66 min). One patient died, one was too infirm for follow-up, and eleven could not be located, leaving 48 patients available for final evaluation (78.7%). The overall incidence of nonunion was 10.4%. Fracture nonunion was less common for undisplaced fractures than for displaced fractures (1 of 21 [4.8%] vs. 4 of 27 [14.8%]). The mean amount of collapse of the neck was 5.45 mm (3.92 mm in undisplaced and 6.64 mm in displaced). Radiographic analysis at final evaluation revealed no implant failures. 62.5% of the patients recovered their prefracture status. The Dual SC screw device appears to be a reliable implant for the treatment of femoral neck fractures. Its design contributes to overcome the implant failures such as a medial migration, cut-out, or back-out; besides, the union rate of this implant was considered superior to that of existing systems. If the early shortening of the neck occurs after this surgery, the surgeons should be considered to keep them partially weight bearing or choose a replacement procedure for such patients.

Performance analytical study of the dual screws actuation mechanism

This paper presents a dual screw actuation mechanism (DSAM) wherein two screws actuate the common sliding platform by connecting two screw nuts with a gear pair. Two dimensionless parameters, namely, the gear ratio between two gears and the pitch ratio between the two screws, are defined to describe the structural characteristics of the DSAM. This study investigates the performance characteristics of a DSAM with respect to gear ratio and pitch ratios. The load distribution between the two screws, which is important in planning the contributions of the two inputs during operation, is discussed. The load capacity is deduced according to the load limits of the two screws with the actuator. The analytical expression for the overall mechanical efficiency of the DSAM is derived from the normal operational power flow mode (two-input-one-output). Based on the Lagrangian formulation, the dynamic coupling term that evaluates the extent to which the inertia torque of one input is affected by the motion variations of the other input is obtained. This performance study provides the fundamental guidelines for the design and operation of a DSAM.

Erratum to: Anterior instrumentation (dual screws single rod system) for the surgical treatment of idiopathic scoliosis in the lumbar area: a prospective study on 33 adolescents and young adults, based on a new system of classification

Erratum to: Anterior instrumentation (dual screws single rod system) for the surgical treatment of idiopathic scoliosis in the lumbar area: a prospective study on 33 adolescents and young adults, based on a new system of classification

Anterior instrumentation (dual screws single rod system) for the surgical treatment of idiopathic scoliosis in the lumbar area: a prospective study on 33 adolescents and young adults, based on a new system of classification

The choice of anterior instrumentation in the treatment of lumbar scoliosis in adolescents and young adults is not a new topic for the authors. The first results achieved using the Dwyer surgical modality were reported by one of the authors followed by the results achieved using Zielke (VDS) instrumentation. Today, new techniques and new instrumentations have been developed that challenge the instrumentation choices. Here we describe how the new system of classification of scoliotic curves we developed has been used as a basis for treating idiopathic scoliosis in lumbar area in adolescents and young adults using an anterior approach. A prospective study was carried out between 1998 and 2010 at two hospital centers on 33 adolescents and young adult with idiopathic lumbar scoliosis involving curves of three kinds, on whom surgical treatment was performed using a single solid rod. Topography of curves: our system of classification includes curves corresponding to the following three type of scoliosis: Type K I: double thoracic and lumbar curves (lumbar predominant) scoliosis (17 cases) mean age 16 years all female patients. Mean Cobb angle of lumbar curve 41°. Mean Cobb angle of thoracic curve 28°. The lumbar curve was left hand convex in 15 cases and right hand convex in 2 cases. Horizontal tilting of L4 mean value 22°. C7 offset mean value 3 cm. Type K IV A: unbalanced thoracolumbar scoliosis (13 cases) mean age 17 years, ten female patients and three male patients. Mean Cobb angle of thoracolumbar curve 39°. The thoracolumbar curve was left hand convex 4 times and right hand convex 9 times. Horizontal tilting of L4 mean value 18°. C 7 offset mean value 2.5 cm. Type K VI A: real lumbar (three cases). Age: 17, 15 and 13 years; all female patients. Cobb angle of the lumbar curve 66°, 29° and 70° (all LH convex). Horizontal tilting of L4: 40°, 20° and 46°. C 7 offset: 7 cm, 1 cm and 4 cm. Surgical instrumentation: We used the EUROS AZUR anterior instrumentation for all the procedures. Cages have been used on five patients at the lower stages. Number of vertebrae instrumented: mean five vertebrae. The patients did not wear postoperative orthosis. Mean duration of procedure: 3 h 50 min. Mean blood loss: 350 cm(3). Type K I scoliosis (17 cases): Mean follow-up: 6 years. Correction of the lumbar curve Cobb angle: the mean angle has been corrected from 41° to 21°. Number of vertebrae instrumented: 4:6 times and 5:11 times. Correction of the upper thoracic curve Cobb angle: mean angle corrected from 28° to 19°. Correction of L4 horizontal tilting: mean residual was 7°. Correction of C 7 offset: mean 0.7 cm. Type K IV A scoliosis (13 cases): mean follow-up: 4 years. Correction of the lumbar curve Cobb angle: the mean angle has been corrected from 39° to 16°. Mean number of instrumented vertebrae: 5 (4:4 times, 5:6 times and 6:3 times.) Correction of L4 horizontal tilting: mean residual 5°. Correction of C 7 offset: mean 0.7 cm. Type K VI A scoliosis (three cases): mean follow-up: 7, 2 and 4 years; Correction of the lumbar curve Cobb angle: the angles have been corrected from 66° to 15°, from 29° to 11° and from 70° to 28°. Number of instrumented vertebrae: 5, 4 and 6. Correction of L4 horizontal tilting: residual tilting of 8°, 7° and 17°. Correction of C 7 offset: 1 cm, 0 cm and 1 cm. There has been no report early or late septic or vascular or neurological complications. Instrumentation failure: there were three cases of screw breakage, all occurred on the lowest implant. Revision surgery was undertaken in both cases, only the last plate needed to be replaced and the rod could be kept without any other modification of the construct. In both cases, fusion has been achieved without any loss of correction. The mean loss of correction of the main curve was 2.5° for the three series. Anterior instrumentation of lumbar idiopathic scoliosis gives highly satisfactory morphological and functional results, since the lumbar musculature is spared and the instrumentation placed at the apex of the curvature has selective effects. Despite our preference and that of other surgeons throughout the world for anterior instrumentation, we are still a minority in comparison with the users of posterior instrumentation. There are several reasons for this reticence, including surgeons' training and ideas about pedicular screw fixation, but the main reason has been the lack of a sufficiently exact system of classification. Previous comparative studies between the anterior and posterior approaches have been biased by the use of an excessively restrictive mode of classification (lumbar/thoracolumbar) of the curves. Real lumbar scoliosis, unbalanced thoracolumbar scoliosis and thoracic and lumbar double curve (lumbar predominant) scoliosis should be properly defined before being compared.

Combining full and semi closed loop synchronous control for dual mechanically coupled ball screw system

The paper presents a synchronous control scheme for a mechanically coupled dual ball screw system applied to wave makers driven by multiple servomotor/ball screw units or machine tools such as those of the gantry type. The hardware system is first established and modelled using a system identification approach. The controller is then designed with pseudo derivative feedback feedforward (PDFF) control. Full and semi-closed-loop controls are analysed and compared in terms of dynamic stiffness, responses and steady-state errors. A hybrid control scheme is then proposed for the investigated system with only one linear scale (i.e., one drive unit is full-and the other semi-closed-loop control). Experiments are conducted to verify the performance by comparing with three conventional synchronous control schemes. The results show that the proposed approach has a much smaller pull-and-drag effect. Also, the positioning accuracy of the system, as well as the synchronous error between the two units is satisfactory.

Design of mechanical presses driven by multi-servomotor

This paper proposes a so-called multi-servomotor parallel driven scheme to construct high capacity mechanical presses. The design method is based on the combination of dual screw actuation unit, parallel mechanism with kinematic redundancy (PMKR) and toggle mechanism with symmetric arrangement. Here, the dual screw actuation unit, which consists of two ball screws driven by two servomotors respectively, acts as a linear actuator. By connection with PMKR, several actuators are incorporated to generate large driving force to push the ram of press via toggle mechanism. To get more power from more linear actuation units, three kinds of 2-, 3-, 6-degree of freedom (DoF) PMKRs with linear actuators are proposed. A 2-DoF PMKR example is studied, and its load capability and accuracy performance are illustrated. Finally, three schematics of 4-, 6- and 12-servomotor mechanical presses are presented. These schemes demonstrate the feasibility of the design method to develop high capacity mechanical presses driven by multi-servomotor.

Short Segment Bone-On-Bone Instrumentation for Adolescent Idiopathic Scoliosis

Prospective case series. To evaluate the clinical and radiologic outcomes of short segment anterior scoliosis surgery with bone-on-bone apposition using a dual screw, dual rod system. Posterior segmental fixation for correction of AIS involves instrumentation of all the vertebrae included in the major curve. Our short segment anterior technique produces similar results by fusion of fewer levels. Forty-five patients operated between 1996 and 2004. Twenty-eight thoracic (Lenke 1) and 17 thoracolumbar (Lenke 5). The mean age was 19 years, 87% were females, and the mean follow-up was 72 months (range 28-121 months). We operated on curves less than 85° with "total discectomy," bone-on-bone apposition, and dual-screw, dual-rod fixation. A mean of five vertebrae (four discs) were instrumented, with a mean operative time of 360 minutes, blood loss of 877 mL and a hospital stay of 9.1 day. Lenke 1. The main preop thoracic curve was 52.5°, final postop curve 27.9°, by fusing five vertebrae, four discs. A spontaneous improvement of 47.5% of the lumbar compensatory curve was seen. The lower tilt angle corrected from 20.9° to 11°. Lenke 5. The preoperative thoracolumbar major curve corrected from 50.5° to 18.3° (final) with fusion of four vertebrae, three discs. A spontaneous improvement of 37.4% occurred in the thoracic compensatory curve. The preop tilt angle improved from 27.7° to 8.3°.The sagittal and coronal balance was restored in all the patients. There were no neurologic, vascular, pulmonary, or implant-related complications. Union occurred within 3 months. All the patients returned to an unrestricted lifestyle within 4 months. We report good results after surgical correction using our short segment bone-on-bone technique. Improvements were noted and maintained, over a 6-year period.

Design of Synthetic Optimizing Neuro Fuzzy Temperature Controller for Dual Screw Profile Plastic Extruder Using Labview

Problem statement: The temperature control in plastic extrusion machine is an important factor to produce high quality plastic products. The first order temperature control system in plastic extrusion comprises of coupling effects, long delay time and large time constants. Controlling temperature is very difficult as the process is multistage process and the system coupled with each other. In order to conquer this problem the system is premeditated with neuro fuzzy controller using LabVIEW. Approach: The existing technique involved is conventional PID controller, Neural controller, mamdani type Fuzzy Logic Controller and the proposed method is neuro fuzzy controller. Results: Manifest feature of the proposed method is smoothing of undesired control signal of conventional PID, neural controller and mamdani type FLC controller. The software incorporated the LabVIEW graphical programming language and MATLAB toolbox were used to design temperature control in plastic extrusion system. Hence neuro fuzzy controller is most powerful approach to retrieve the adaptiveness in the case of nonlinear system. Conclusion: The tuning of the controller was synchronized with the controlled variable and allowing the process at its desired operating condition. The results indicated that the use of proposed controller improve the process in terms of time domain specification, set point tracking and also reject disturbances with optimum stability.

About Dual Spherical Wrist Motion and Its Trajectory Surface as a Ruled Surface

Solid object rotations or rotations of unit real vectors are often used in robotic moves. Yet, due to the complexity of calculations in kinematics analysis, quaternions began to be used in robotic moves. Quaternions help us to calculate rotations in reel space, and rotation and translation in dual space. Furthermore, we can easily define a screw or an axis through dual vectors. In recent years, there has been efficient studies in mechanics analysis by using dual quaternions and screw moves. In this study, we transferred the well known sequential and modular methods for the rotations being formed in real spherical wrist moves to dual space. Hence, while we rotate the unit vectors only in real space, now we can rotate screws .Hence, while we rotate the unit vectors only in real space, now we can rotate screws or the axis in the dual spherical mechanisms in dual kinematics. Through this study, by being switched to dual spherical mechanism the first time, we will see that we can carry out what we do with unit vectors in real space as well as in dual space. Furthermore, while the orbits drawn by the joint moves are curves in reel spherical wrist moves, the orbits drawn by the joint moves are ruled surfaces in dual spherical wrist moves. We think that this situation would establish a base for different mechanics studies.

Biomechanical effects of the extent of sacrectomy on the stability of lumbo-iliac reconstruction using iliac screw techniques: What level of sacrectomy requires the bilateral dual iliac screw technique?

Background Although both single and dual iliac screw techniques are used in spino-pelvic reconstruction following sacrectomy for treating sacral tumors, the basis for choosing between the two techniques for different instability types remains undetermined. The purpose of this study was to evaluate the effects of the extent of sacrectomy on the stability of the lumbo-iliac fixation construct using single and dual iliac screw techniques. Methods Nine human L2-pelvic specimens were tested for their intact condition simulated by L3–L5 pedicle screw fixation. Sequential partial sacrectomies and L3-iliac fixation using bilateral single and dual iliac screws were conducted on the same specimens as follows: under-S1 sacrectomy + single screw, under-½S1 sacrectomy + single screw, one-side sacroiliac joint resection + single screw, total sacrectomy + single screw, and total sacrectomy + dual screw. Biomechanical testing was performed on a material testing machine for evaluating the stiffness of the L3-iliac fixation construct in compression and torsion. Findings Single iliac screw technique was found to effectively restore the local stability in under-½S1 sacrectomy. However, it could not provide adequate stability for further resection of one-side sacroiliac joint in torsion and total sacrectomy in compression ( P < 0.05). On the other hand, dual iliac screw technique could restore the stability to the intact condition after total sacrectomy in both compression and torsion. Interpretation The single iliac screw technique for L3-iliac fixation could effectively restore the local stability for under-½S1 sacrectomy. However, for instabilities of the under-½S1 sacrectomy with one-side sacroiliac joint resection or total sacrectomy, the dual iliac screw technique should be considered.

Biomechanical advantages of dual iliac screws over single ones in lumbo-iliac fixation construct

Objective To evaluate the biomechanical effects of single short, single long and dual short iliac screws on the stability of lumbo-iliac fixation construct. Methods L2-pelvic specimens were harvested from 7 fresh human cadavers. Following the test of the intact state simulated by L3-L5 pedicle screw fixation, the destabilization by total sacrectomy and L3-iliac screw-rod reconstructions with 3 placements of iliac screws were conducted as follows: bilateral single short iliac screws in Group A; bilateral single long iliac screws in Group B; bilateral dual short iliac screws in Group C. The 3 iliac screw fixations were preformed in the same specimens in a random order, and the lengths of short and long iliac screws were 70 mm and 130 mm, respectively. Biomechanical testing was performed on a material testing machine under 800 N compression and 7 Nm torsion loading modes for construct stiffness evaluation. Results In compression, the constructs in Groups A, B, C obtained 73%, 76%, and 108% of the initial compression stiffness, respectively. No significant differences were demonstrated between Groups A and B ( P > 0. 05), but the 2 groups showed obviously lower construct compression stiffness than the intact state and Group C ( P 0. 05). However, Groups A and B provided markedly lower construct torsion stiffness than the other 2 conditions (P < 0. 05). Conclusions Following total sacrectomy, it is rather difficult to restore the initial local stability by using bilateral single long iliac screws. However, the dual iliac screws when compared with the single ones can provide much higher construct stability comparable to the initial state. Key words: Lumbosacral region; Joint instability; Lumbo-iliac reconstruction; Bone nails; Biomechanics

Comparison of migration behavior between single and dual lag screw implants for intertrochanteric fracture fixation.

BackgroundLag screw cut-out failure following fixation of unstable intertrochanteric fractures in osteoporotic bone remains an unsolved challenge. This study tested if resistance to cut-out failure can be improved by using a dual lag screw implant in place of a single lag screw implant. Migration behavior and cut-out resistance of a single and a dual lag screw implant were comparatively evaluated in surrogate specimens using an established laboratory model of hip screw cut-out failure.MethodsFive dual lag screw implants (Endovis, Citieffe) and five single lag screw implants (DHS, Synthes) were tested in the Hip Implant Performance Simulator (HIPS) of the Legacy Biomechanics Laboratory. This model simulated osteoporotic bone, an unstable fracture, and biaxial rocking motion representative of hip loading during normal gait. All constructs were loaded up to 20,000 cycles of 1.45 kN peak magnitude under biaxial rocking motion. The migration kinematics was continuously monitored with 6-degrees of freedom motion tracking system and the number of cycles to implant cut-out was recorded.ResultsThe dual lag screw implant exhibited significantly less migration and sustained more loading cycles in comparison to the DHS single lag screw. All DHS constructs failed before 20,000 cycles, on average at 6,638 ± 2,837 cycles either by cut-out or permanent screw bending. At failure, DHS constructs exhibited 10.8 ± 2.3° varus collapse and 15.5 ± 9.5° rotation around the lag screw axis. Four out of five dual screws constructs sustained 20,000 loading cycles. One dual screw specimens sustained cut-out by medial migration of the distal screw after 10,054 cycles. At test end, varus collapse and neck rotation in dual screws implants advanced to 3.7 ± 1.7° and 1.6 ± 1.0°, respectively.ConclusionThe single and double lag screw implants demonstrated a significantly different migration resistance in surrogate specimens under gait loading simulation with the HIPS model. In this model, the double screw construct provided significantly greater resistance against varus collapse and neck rotation in comparison to a standard DHS lag screw implant.

The Position of the Aorta Relative to the Spine Before and After Anterior Instrumentation in Right Thoracic Scoliosis

Preoperative magnetic resonance images (MRI) and postoperative axial computed tomography (CT) scans in 25 consecutive patients with idiopathic right thoracic adolescent scoliosis (AIS) and anterior correction and fusion with a dual rod system were analyzed in a prospective study. Evaluation of the spatial relations between the vertebral body and the aorta and the relative migration of the aorta due to the anterior correction and instrumentation in right thoracic scoliosis patients. In anterior scoliosis surgery, bicortical screw purchase is performed to increase pullout strength. However, impingement of the aorta due to excessive contralateral screw penetration has been reported, especially after endoscopic instrumentation. For a safe screw placement, knowledge of both the preoperative topographic relation of aorta and vertebral body and its changes due to surgical correction is crucial. Recent studies reported on a more lateral and posterior position of the aorta in AIS patients. However, there are hardly any data on the changes of the aortic position after anterior curve correction available in the current literature. All 25 patients underwent an identical anterior surgical technique with standard open approach and dual rod instrumentation of the primary curve. Preoperative MRI and postoperative sequential CT scans of 180 vertebrae were analyzed with respect to following parameters: vertebral body width and depth, diameter of the aorta, closest distance between aorta and the vertebral body, the aorta-vertebral angle, and the position of the aorta in relation to the spinal canal. Before surgery, the aorta is positioned posterolaterally with an aorta-vertebral angle of between 78 degrees and 92 degrees (between T5 and T10). Between T11 and L2, the aorta is positioned more anteromedially with an aorta-vertebral angle from 62 degrees (T11) to 16 degrees (L2). After surgery, the aorta has migrated from a posterolateral to a more anteromedial position. This migration is maximal at the apex vertebra with an average change of the aorta-vertebral angle of 31.4 degrees . Whereas the distance between the aorta and the vertebral body increases at the upper and lower fusion levels, the aorta moves significantly closer to the vertebral body at the curve apex due to surgical correction. In patients with thoracic hypokyphosis, the aorta is positioned significantly more posterior than in patients with hyperkyphosis. This MRI and CT based study of 25 patients with thoracic AIS treated by standard open dual rod and dual screw instrumentation demonstrates a migration of the aorta by 31 degrees from a more posterolateral position before surgery to a more anteromedial position after surgery at the curve apex. Scoliosis surgeons should be aware of these changes; any excessive contralateral screw penetration must be avoided at any level.

Anterior dual rod instrumentation in idiopathic thoracic scoliosis

For anterior correction and instrumentation of thoracic curves single rod techniques are widely used. Disadvantages of this technique include screw pullouts, rod fractures and limited control of kyphosis. This is a prospective study of 23 consecutive patients with idiopathic thoracic scoliosis treated with a new anterior dual rod system. Aim of the study was to evaluate the safety and efficacy of this new technique in the surgical treatment of idiopathic thoracic scoliosis. To the best knowledge of the authors, this is the largest series on dual rod dual screw instrumentation over the entire fusion length in thoracic scoliosis. Twenty-three patients with an average age of 15 years were surgically treated with a new anterior dual rod system through a standard open double thoracotomy approach. Average clinical and radiological follow-up was 28 months (24-46 months). Fusion was carried out mostly from end-to-end vertebra. The primary curve was corrected from 66.6 degrees to 28.3 degrees (57.5% correction) with an average loss of correction of 2.0 degrees at Cobb levels and of 1.3 degrees at fusion levels. Spontaneous correction of the secondary lumbar curve averaged 43.2% (preoperative Cobb angle 41.2 degrees ). The apical vertebral rotation was corrected by 41.1% with a consecutive correction of the rib hump of clinically 66.7%. The thoracic kyphosis measured 29.2 degrees preoperatively and 33.6 degrees at follow-up. In seven patients with a preoperative hyperkyphosis of on average 47.3 degrees thoracic kyphosis was corrected to 41.0 degrees . This new instrumentation enables an entire dual rod instrumentation over the whole thoracic fusion length. It offers primary stability without the need of postoperative bracing. Dual screw dual rod instrumentation offers the advantages of a high screw pullout resistance, an increased overall stability and satisfactory sagittal plane control.

Anterior Dual Rod Instrumentation in Idiopathic Thoracic Scoliosis

Axial computed tomography scans (CT) in 20 consecutive patients with idiopathic right thoracic scoliosis and anterior correction and fusion with a dual rod dual screw system. CT evaluation of screw position in anterior dual rod instrumentation relative to the aorta and the spinal canal. In anterior scoliosis surgery, bicortical screw purchase is used to increase pullout strength. However, impingement of the aorta due to excessive contralateral screw penetration has been reported, especially after endoscopic instrumentation. Data on the accuracy of dual screw instrumentation in thoracic scoliosis are missing. All 20 patients underwent an identical anterior surgical technique with double thoracotomy approach and dual rod instrumentation of the primary curve. Postoperative sequential CT scans were analyzed with respect to following parameters: vertebral body width and depth, diameter of the aorta, distance from the aorta to the closest point of the vertebral body cortex, distance between the tip of the screws and the aorta, distance between the screw and the spinal canal, and the amount of contralateral screw penetration. A total amount of 226 screws were evaluated. All screws were placed correctly without any critical proximity to the aorta or spinal canal. A total of 198 of 226 screws (88%) had a bicortical purchase. Thirteen screw tips (5.8%) were within 1 to 3 mm proximity to the aorta. All other screws were more than 3 mm distant from the aorta. The closest proximity of the screw tips to the thoracic aorta was found at the upper end vertebrae (T5, T6, or T7). There were no screws perforating the spinal canal. Anterior instrumentation and correction of thoracic scoliosis with a dual rod dual screw system enable a correct and safe screw placement using a standard open approach. Excessive bicortical screw perforation should be avoided in order not to endanger the thoracic aorta.

347 臨床用ボーンスクリューとダブルロックスクリューにおける回旋および曲げ接合強度

347 臨床用ボーンスクリューとダブルロックスクリューにおける回旋および曲げ接合強度

Theory of Point Contact Restraint and Qualitative Analysis of Robot Grasping

This paper presents a geometrical representation of robot grasping and a definition of relative form closure of point contact restraint based on the concepts of positive linear combination,affine combination,convex combination,etc.in the screw space.The dual equivalence theorem,topological equivalence theorem and algebraic equivalence theorem are derived from the defined restraint cone and freedom cone in the dual screw spaces.A J0-function method of computer-aided grasp planning is implemented more efficiently than other proposed methods.The states of restraint and instantaneous motion of a rigid body grasped by a set of point contacts are specified by the unisense degrees of freedom and unisense degrees of restraint.Finally,a quality measure of robot grasping is provided for the synthesis procedure of relatively form-closed grasp.

Laboratory comparison of the cannulated Herbert bone screw with ASIF cancellous lag screws

The compression produced by and the resistance to pullout of the 6.5 mm cannulated Herbert screw were compared with those of ASIF headed screws. The latter were tested with and without washers and in the following sizes: 4.5 mm cortical, 6.5 mm cancellous with a 16 mm threaded segment, and 6.5 mm cancellous with a 32 mm threaded segment. Polyurethane foam was used as a substitute for cancellous bone and ASIF artificial bone for corticocancellous bone. The compression produced by a cancellous lag screw with a washer was significantly greater than that produced by a Herbert screw of equivalent size (p < 0.05). When the screws were tested using the corticocancellous composite the ASIF cancellous screw without a washer produced significantly greater compression (p < 0.05); when used with a washer the difference was highly significant (p < 0.001). The dual pitch Herbert screw is not appropriate for the management of fractures in which compression is of greater importance than the need to avoid prominence of the screw head.

Dynamic Analysis of Spatial Mechanisms Using Dual Successive Screw Method and D’Alembert’s Principle

The method based on the application of the successive dual screw displacements and d’Alembert’s principle, is developed to perform kinetostatic and dynamic analysis of space mechanisms with lower kinematic pairs. The method is applied to demonstrate its usefulness in performing kinetostatic and dynamic analysis of single-loop, four-link, five-link, six-link and seven-link mechanisms with lower kinematic pairs.

A spatial four-link mechanism having two prismatic pairs

It is demonstrated that there exists a four-link mechanism with one revolute, two prismatic and one cylindrical joints. This is shown by use of dual screw vector algebra. This paper was first presented at the Third Conference on Fundamental Problems in the Theory of Machines and Mechanisms in Moscow (1961) and published in these Transactions,††Tpy/wlы tpetвero coвeщaния пo ocнляeмaм teopцл maщин и mexaниэmob, maщtиэ, mockba, 1963. in the volume Analysis and Synthesis of Mechanisms (1963).