ROBOT'S MOTION ERROR AND ONLINE COMPENSATION BASED ON FORCE SENSOR

Robot＇s dynamic motion error and on-line compensation based on multi-axis force sensor are dealt with.It is revealed that the reasons of the error are formed and the relations of the error are delivered.A motion equation of robot＇s termination with the error is established,and then,an error matrix and an error compensation matrix of the motion equation are also defined.An on-line error＇s compensation method is put forward to decrease the displacement error,which is a degree of millimeter,shown by the result of simulation of PUMA562 robot.

A novel method of evaluating the lift force on the bluff body based on Noca's flux equation

The influence of experimental error on lift force evaluated by Noca’s flux equation is studied based on adding errors into the direct numerical simulation data for flow past cylinder at Re = 100. As Noca suggested using the low-pass filter to get rid of the high-frequency noise in the evaluated lift force, we verify that his method is inapplicable for dealing with the dataset of 1% experimental error, although the precision is acceptable in practice. To overcome this defect, a novel method is proposed in this paper. The average of the lift forces calculated by using multiple control volume is taken as the evaluation before applying the low-pass filter. The method is applied to an experimental data for flow past a cylinder at approximately Re = 900 to verify its validation. The results show that it improves much better on evaluating the lift forces.

Sensitivity analysis for a type of statically stable sailcrafts

Two types of sensitivities are proposed for stat- ically stable sailcrafts. One type is the sensitivities of solar-radiation-pressure force with respect to position of the center of mass, and the other type is the sensitivities of solar-radiation-pressure force with respect to attitude. The two types of sensitivities represent how the solar-radiation- pressure force changes with the position of mass center and the attitude. Sailcrafts with larger sensitivities undergo larger error of the solar-radiation-pressure force, leading to larger orbit error, as demonstrated by simulation. Then as a case study, detailed formulas are derived to calculate the sensi- tivities for sailcrafts with four triangular sails. According to these formulas, in order to reduce both types of sensitivities, the angle between opposed sails should not be too large, and the center of mass should be as close to the axis of symmetry of the four sails as possible and as far away from the center of pressure of the sailcraft as possible.

Influence mechanism of machining angles on force induced error and their selection in five axis bullnose end milling

In the machining of complicated surfaces,the cutters with large length/diameter ratios are used widely and the deformation of the machining system is one of the principal error sources.During the process planning stage,the cutting direction angle,the cutter lead and tilt angles are usually optimized to minimize the force induced error.It may lead to a low machining efficiency for bullnose end mills,as the material removal rates are different largely for different machining angles.In this paper,the influence mechanism of the machining angles on the force induced error is studied based on the models of the instantaneous cutting force when the cutter flute traveling through the cutting contact point and the stiffness of the machining system.In order to evaluate the machining angles,the force induced error/efficiency indicator(FEI)is defined as the division of the force induced error and the equal volume sphere of the removed material.FEI is dimensionless,with the lower FEI,the lower force induced error and the higher machining efficiency.For optimal selection of the machining angles,the critical FEI is calculated with the constraint of force induced error and the desired material removal rate,and the critical FEI separate the set of the machining angles into two subsets.After the feed rate scheduling process,the machining angles in the optimal subset would have higher machining accuracy and efficiency,while the machining angles in the other subset have lower machining accuracy and efficiency.Through the machining experiment of five axis machining and freeform surface machining,the effectiveness and superiority of the proposed FEI method is verified with a bullnose end mill,which can improve the machining efficiency with the constraint of force induced error.