Maximum Step Length Research Articles

A new decision algorithm of maximum allowable step length for five‐axis table‐tilting type machining

Traditional CAM algorithms evaluate the cutting error only based on the geometry of the sculptured surfaces. The kinematic parameters, such as rotational angles, machine structure, and tool geometry, are not considered until the post‐processing stage. When using the tool paths generated by traditional algorithms, the corresponding cutting errors may be larger than expected due to rotation. Therefore, the estimation algorithm presented in this paper considers not only surface geometry but also kinematic parameters. Compared to traditional CAM algorithms, simulation results show that the step lengths are varied adaptively, and cutting errors are reduced.

A Note on the Calculation of Step-Lengths in Interior-Point Methods for Semidefinite Programming

In each iteration of an interior-point method for semidefinite programming, the maximum step-length that can be taken by the iterate while maintaining the positive semidefiniteness constraint needs to be estimated. In this note, we show how the maximum step-length can be estimated via the Lanczos iteration, a standard iterative method for estimating the extremal eigenvalues of a matrix. We also give a posteriori error bounds for the estimate. Numerical results on the performance of the proposed method against two commonly used methods for calculating step-lengths (backtracking via Cholesky factorizations and exact eigenvalues computations) are included.

A clinical measure of maximal and rapid stepping in older women.

In older adults, clinical measures have been used to assess fall risk based on the ability to maintain stance or to complete a functional task. However, in an impending fall situation, a stepping response is often used when strategies to maintain stance are inadequate. We examined how maximal and rapid stepping performance might differ among healthy young, healthy older, and balance-impaired older adults, and how this stepping performance related to other measures of balance and fall risk. Young (Y; n = 12; mean age, 21 years), unimpaired older (UO; n = 12; mean age, 69 years), and balance-impaired older women IO; n = 10; mean age, 77 years) were tested in their ability to take a maximal step (Maximum Step Length or MSL) and in their ability to take rapid steps in three directions (front, side, and back), termed the Rapid Step Test (RST). Time to complete the RST and stepping errors occurring during the RST were noted. The IO group, compared with the Y and UO groups, demonstrated significantly poorer balance and higher fall risk, based on performance on tasks such as unipedal stance. Mean MSL was significantly higher (by 16%) in the Y than in the UO group and in the UO (by 30%) than in the IO group. Mean RST time was significantly faster in the Y group versus the UO group (by 24%) and in the UO group versus the IO group (by 15%). Mean RST errors tended to be higher in the UO than in the Y group, but were significantly higher only in the UO versus the IO group. Both MSL and RST time correlated strongly (0.5 to 0.8) with other measures of balance and fall risk including unipedal stance, tandem walk, leg strength, and the Activities-Specific Balance Confidence (ABC) scale. We found substantial declines in the ability of both unimpaired and balance-impaired older adults to step maximally and to step rapidly. Stepping performance is closely related to other measures of balance and fall risk and might be considered in future studies as a predictor of falls and fall-related injuries.

Cutting Error Analysis for Table-Tilting Type Four-Axis NC Machines

Current computer-aided manufacturing (CAM) systems generate cutter contact points (CC points), cutter location points (CL points) and cutter orientation angles (CO angles) based only on the sculptured surface geometry. However, under certain conditions, the cutting errors of multiple-axis NC machines are larger than expected when using these CC, CL and CO data. This is because the cutting errors of multiple-axis NC machines depend on the machines structure data as well as on the geometry of the machined part. An algorithm is developed in this paper to estimate the cutting error and calculate the maximum allowable step length for table-tilting type four-axis NC machines. It is shown that the cutting error is proportional to the distance between the machined arc and the centre of the rotational axis. Therefore, the step length should be chosen to be smaller when the machined arc is displaced from the rotational axis.

Estimation of Maximum Allowable Step Length for Five-Axis Cylindrical Machining

Five-axis cylindrical machining is the only way to machine some complicated sculptured surfaces, such as the wheel surfaces of turbo compressors. Current computer-aided manufacturing (CAM) algorithms for five-axis cylindrical machining only consider the surfaces’ geometric information when generating cutter contact points (CC points). Hence, the step length, which is the distance between two CC points, is determined only by the surface parameters for these CAM algorithms. Because of tool-axis rotation, the actual cut trajectory within each step is no longer a straight line passing through two consecutive CC points for five-axis machining. Thus the cut error and the maximum allowable step length should depend on the structural parameters of NC machines as well as the surface's geometry. This paper develops a new algorithm to estimate the maximum allowable step length based on the cut error of five-axis cylindrical machining, and shows that this algorithm provides better estimation than traditional algorithms.

Cutting errors analysis for spindle-tilting type 5-axis NC machines

Current computer-aided manufacturing (CAM) systems generate cutter contact points (CC points), cutter location points (CL points) and cutter orientation angles (CO angles) based only on the sculptured surface geometry. However, under certain situations, the cutting errors of 5-axis NC machines are larger than expected using these CC, CL and CO data. It is shown in this paper that the cutting error depends on the structures of 5-axis NC machines as well as the surface geometry. A new algorithm has been developed to estimate the cutting error and calculate the maximum allowable step length for spindle-tilting type 5-axis NC machines. Simulation results show that the new algorithm provides better estimation on the cutting errors for spindle-tilting type 5-axis NC machines.

THE EFFECTS OF COMBINED UPHILL-DOWNHILL SPRINT TRAINING ON BIOMECHANICAL VARIABLES

1467 The aims of the present study were to assess the efficacy of a novel combined uphill-horizontal-downhill sprint training method and its effects on the kinematic characteristics of sprinting running and on a battery of vertical jumps. Twenty-seven male physical education students comprised the two experimental (A and B) and one control (C) groups of the study. Groups A and B sprinted maximally with the same intensity and volume of exercise (3 times a week) over an 8-week period. The training programme consisted of 6 repetitions of 80 m sprints until the 4th week after which 1 repetition was added for each of the remaining weeks where the recovery periods between the repetitions were 4-6 min. Group A was trained on a uphill-downhill platform,(80 m long, 10 m flat, 20 m uphill at 3 ° slope, 10 m flat, 20 m downhill at 3 ° slope and 20 m flat) and Group B was trained on the horizontal. Pre and post training tests were employed to measure the effects of training on maximal step velocity (MSV), step rate (SR) and step length (SL), contact time(CT) and flight time (FT), as well as to a battery of vertical jumps. Only Group A increased MSV, significantly with training by 4.6% (8.05 ± 0.68 to 8.43 ± 0.69 m.s-1P<0.01), which was mainly due to an increase of SR by 4.6% (3.90 ± 0.29 to 4.09 ± 0.30 Hz, P<0.05). For the battery of vertical jumps the only noteworthy change was that for the 50 cm drop jump which was improved by 2.2% but not statistically significant. The findings of the present study suggest that this novel combined uphill-horizontal-downhill training method produced a significant improvement in performance compared to the same running performed on horizontal.

The effectiveness of placebo muscle stimulation in quadriceps muscle rehabilitation: a preliminary evaluation

Objectives: the objective of this study was to evaluate the effect of placebo and ‘active’ muscle stimulation in the rehabilitation of quadriceps muscle function in patients with osteoarthritis of the knee. Design: this study compares data collected from four randomly allocated, blindly delivered stimulation patterns: one placebo; one uniform frequency and two variable frequency. Quadriceps muscle stimulation was undertaken over a 6 week period for 3 h per day using a portable electrical stimulator (DMI, PSI). Participants: thirty patients with osteoarthritis, affecting one or both of their knee jonts, were recruited into the trial. All were recruited from a waiting list for knee joint replacement. Main outcome measures: the following measures of quadriceps muscle and lower limbfunction were undertaken pre and post electrotherapy treatment: quadriceps muscle isometric torque; quadriceps muscle cross-sectional area; timed sit-to-stand; timed velocity of walking and step length. Results: no significant difference in maximum voluntary isometric torque, velocity ofwalking, step length and cross-sectional area (p=0.66, 0.86, 0.53 and 0.77 respectively) was observed between the average of the three ‘active’ stimulation groups compared with the control. This picture was not repeated with an analysis of sit-to-stand time, where there was a significant difference between the placebo and the average of the three other groups (p=0.03). In this case the placebo group performed considerably worse than the three active treatment groups by 17.5%, 95% CI (confidence/intervals) (−25.21,−1.165). Conclusions: this paper describes a model to illustrate the potentially powerful effects placebo treatment can have on human physiological parameters. These effects are discussed in relation to potential confounding variables and the limitations of this study. Suggestions for further research and the clinical potential of this type of treatment are discussed.

Monte Carlo Study of a Hydrogenous Plasma near the Ionization Temperature

Results of a recent Monte Carlo study of a hydrogenous plasma near the ionization temperature show that distribution functions obtained are unusually sensitive to two parameters. The first is the cutoff imposed at small radii on the Coulomb potential between unlike particles, and it becomes necessary to consider quantum-mechanical effects at these radii. The second is the maximum step length $\ensuremath{\Delta}$ through which the particles are allowed to move in the Monte Carlo procedure. It appears that near the ionization temperature the plasma behaves as a mixture of two phases, one ionized, the other un-ionized, and the magnitude chosen for $\ensuremath{\Delta}$ influences which phase dominates.