Comparison of Pixel-based Position Input and Direct Acceleration Input for Virtual Stick Balancing Tests

A virtual stick balancing environment is developed using a computer mouse as input device. The development process is presented both on the hardware and software level. Two possible concepts are suggested to obtain the acceleration of the input device: discrete differentiation of the cursor position measured in pixels on the screen and by direct measurements via an Inertial Measurement Unit (IMU). The comparison of the inputs is carried out with test measurements using a crank mechanism. The measured signals are compared to the prescribed motion of the mechanism and it is shown that the IMU-based input signal fits better to the prescribed motion than the pixel-based input signal. The pixel-based input can also be applied after additional filtering, but this presents an extra computational delay in the feedback loop

Parametric Study of Changes in Human Balancing Skill by Repeated Balancing Trials on Rolling Balance Board

Dynamic balance conditions were realized by asking eight volunteers to stand on uniaxial balance board with adjustable geometry and to carry out 60 s long balancing trials. Four different balance board geometry were used, each associated with different difficulty level. Balancing trials were repeated five times weekly (learning period) in order to test improvement of balancing skill. The measurement was repeated eight weeks after the learning period in order to check the persistence of the balancing skill (confirmation session). Oscillations of ankle angle and hip angle were monitored by OptiTrack motion capture system and four stabilometry parameters were used to characterize improvement in balancing performance, namely, Standard Deviation (STD), Largest Amplitude (LA), Normalized Path Length (NPL) and Mean Power Frequency (MPF). STD and NPL show similar tendency to the preliminary expectations, therefore they can be considered as good measures to describe balancing performance. Results show that subjects used ankle strategy for the less difficult balance board configurations, while for the more difficult tasks, hip strategy was also involved. Changes in STD and NPL during the learning period showed that the improvement and the persistence in balancing skill is more significant for more difficult balancing tasks

MECHANICAL MODEL FOR HUMAN BALANCING ON ROLLING BALANCE BOARD

A two-degree-of-freedom mechanical model was developed to analyze human balancing on rolling balance board in the frontal plane. The human nervous system is modeled as a proportionalderivative controller with constant feedback delay. The radius R of the wheels and the board distance h measured from the center of the wheel are adjustable parameters. Simulation results using the mechanical model were compared with real balancing trials recorded by an OptiTrack motion capture system. The goal of the paper is to investigate whether the two-degree-of-freedom model is accurate enough to model the balancing task and to introduce a stabilometry parameter in order to characterize balancing skill in case of different set of R and h. The conclusion is that the angle of the upper body and the angle of the head also play an important role in the balancing process therefore a three- or four-degree-of-freedom model is more appropriate

MECHANICAL MODEL FOR HUMAN BALANCING ON ROLLING BALANCE BOARD

A two-degree-of-freedom mechanical model was developed to analyze human balancing on rolling balance board in the frontal plane. The human nervous system is modeled as a proportionalderivative controller with constant feedback delay. The radius R of the wheels and the board distance h measured from the center of the wheel are adjustable parameters. Simulation results using the mechanical model were compared with real balancing trials recorded by an OptiTrack motion capture system. The goal of the paper is to investigate whether the two-degree-of-freedom model is accurate enough to model the balancing task and to introduce a stabilometry parameter in order to characterize balancing skill in case of different set of R and h. The conclusion is that the angle of the upper body and the angle of the head also play an important role in the balancing process therefore a three- or four-degree-of-freedom model is more appropriate

Effects of radial immersion and cutting direction on chatter instability

ABSTRACT Low radial immersion end-milling involves intermittent cutting. If the tool is flexible, its motion in both the x-and ydirections affects the chip load and cutting forces, leading to chatter instability under certain conditions. Interrupted cutting complicates stability analysis by imposing sharp periodic variations in the dynamic model. Stability predictions for the 2-DOF model differ significantly from prior 1-DOF models of interrupted cutting. In this paper stability boundaries of the 2-DOF milling process are determined by three techniques and compared: (1) a frequency-domain technique developed b

On the Approximation of Delayed Systems by Taylor Series Expansion

It is known that stability properties of delay-differential equations are not preserved by Taylor series expansion of the delayed term. Still, this technique is often used to approximate delayed systems by ordinary differential equations in different engineering and biological applications. In this brief, it is demonstrated through some simple second-order scalar systems that low-order Taylor series expansion of the delayed term approximates the asymptotic behavior of the original delayed system only for certain parameter regions, while for high-order expansions, the approximate system is unstable independently of the system parameters

Conditions for stabilizability of time-delay systems with real-rooted plant

International audienceIn this paper we consider the-stabilization of th-order linear time-invariant (LTI) dynamical systems using Multiplicity-Induced-Dominancy (MID)-based controller design in the presence of delays in the input or the output channels. A sufficient condition is given for the dominancy of a real root with multiplicity at least n + 1 and at least using an integral factorization of the corresponding characteristic function. A necessary condition for-stabilizability is analyzed utilizing the property that the derivative of \alpha-stable quasipolynomial is also-stable under certain conditions. Sufficient and necessary conditions are given for systems with real-rooted open loop characteristic function: the delay intervals are determined where the conditions for dominancy and \alpha-stabilizability are satisfied. The efficiency of the proposed controller design is shown in the case of a multi-link inverted pendulum

Calculation of the critical delay for the double inverted pendulum

International audienceSingle and double inverted pendulum systems subjected to delayed state feedback are analyzed in terms of stabilizability. The maximum (critical) delay that allows a stable closed-loop system is determined via the multiplicity-induced-dominancy property of the characteristic roots, that is the dominant (rightmost) roots are associated with higher multiplicity under certain conditions of the system parameters. Other methods such as tracking the changes of the D-curves with increasing delay and the Walton-Marshall method are also demonstrated for the example of the single pendulum. For the double inverted pendulum subjected to full state feedback, the number of control gains is four, and application of numerical methods requires therefore high computational effort (i.e. optimization in a four-dimensional space). It is shown that, with the multiplicity-induced-dominancy-based approach, the critical delay and the associated control gains can be determined directly using the characteristic equation and its derivatives