P. Pintado

Kinematic Model of a New Staircase Climbing Wheelchair and its Experimental Validation

This paper describes the mechanical devices, the movements and the associated kinematic models of a novel wheelchair prototype capable of climbing staircases. The key feature of the mechanical design is the use of two decoupled mechanisms in each axle, one used to negotiate steps, and the other to position the axle with respect to the chair to accommodate the overall slope. This decoupling makes possible many different climbing strategies, the overall mechanism being extraordinarily versatile from a control point of view. Kinematic models have been developed for the different mechanical configurations that appear during all the ascend/descend processes. These models are required to control the actuators of the wheelchair in such a way that its centre of mass is able to follow arbitrary spatial trajectories. This is very important as one has to design very smooth spatial trajectories, keeping a near null inclination of the seat all the time in order to guarantee the comfort of the passenger, usually a handicapped or injured person. A real prototype is presented, and experimental results are reported that show the efficiency of the mechanism and the accuracy of the kinematic models developed.

Environment adaptation of a new staircase-climbing wheelchair

Abstract This paper describes the mechanical devices conforming a novel wheelchair prototype capable of climbing staircases. The key feature of the mechanical design is the use of two decoupled mechanisms in each axle, one to negotiate steps, and the other to position the axle with respect to the chair to accommodate the overall slope. This design simplifies the control task substantially. Kinematic models are necessary to describe the behavior of the system and to control the actuated degrees of freedom of the wheelchair to ensure the passenger’s comfort. The choice of a good climbing strategy simplifies the control and decreases the power consumption of the wheelchair. In particular, we demonstrate that if the movement of the wheelchair has the same slope as the racks or the same slope as the terrain that supports the wheel axles (depending on the configuration mechanism), control is easier and power consumption is less. Experimental results are reported which show the behavior of the prototype as it moves over different situations: (a) ascending a single step of different heights using different climbing strategies; and (b) climbing a staircase using an appropriate climbing strategy that simplifies the control and reduces the power consumption of the wheelchair.

Coordinated motion of a new staircase climbing wheelchair with increased passenger comfort

This paper describes the mechanical devices, the movements and the trajectory generation of a novel wheelchair prototype capable of climbing staircases. The key feature of the mechanical design is the use of two decoupled mechanisms for each axle, one used to negotiate steps, and the other to position the axle with respect to the chair to accommodate the overall slope. This decoupling makes many different climbing strategies possible, the overall mechanism becoming extraordinarily versatile from a control point of view. A control system is necessary to synchronize the movements of all the actuators of the wheelchair so that its centre of mass can follow arbitrary spatial trajectories. Different trajectories have been designed in order to keep the seat as erect as possible to guarantee passenger comfort. Experimental results with the real prototype are reported which show the efficiency of our mechanism, the accuracy of the developed kinematic models for control, and the comparison of comfort for two different spatial trajectories

Automatic measurement of field-dependent elastic modulus and damping by laser Doppler vibrometry

A method for characterizing the magnetoelastic dependence of both Youngs modulus and damping on the magnetic field is presented. It is based on laser Doppler vibrometry and free longitudinal vibration in soft ferromagnetic rods and wires, and offers a broad range of improved features including accuracy, lack of interaction with the sample, speed of measurement, full automation, high resolution and the possibility of stress-dependence studies. All these allow samples to be perfectly characterized in the full magnetic field range, estimating the behaviour of the specimen as different magnetization curves are followed and discovering critical points that had been overlooked in previous works. As an example, the magnetoelastic characterization of nickel rods is described, and excellent results are obtained which are consistent with the hysteresis loop of nickel and the theory of magnetic domains in ferromagnetic materials.

An adaptive pneumatic suspension system for improving ride comfort and handling

The paper describes an adaptive pneumatic suspension system that can improve both comfort and handling. Each air spring in the vehicle is connected to an auxiliary tank via two connecting pipes of different sizes. Choosing the connecting pipe with larger diameter and shorter length renders a compliant suspension which improves comfort. Conversely, choosing the connecting pipe with smaller diameter and longer length makes the suspension stiffer which favors handling. Toggling between configurations is fast, efficient, and easily done by simply opening or closing the corresponding electrovalves. The proposed adaptive system requires a GPS receiver and access to two pieces of information regarding the road at every location: the International Roughness Index and the curve radius (if not infinite). This information is used to predict road-induced vibrations and evaluate comfort with the ISO 2631 standard, as well as forecast roll angles and settling times for handling assessment. These predictions are used to select the most appropriate configuration.

A semi-active vehicle suspension based on pneumatic springs and magnetorheological dampers:

Semi-active and active suspensions can improve both ride comfort and handling compared to passive suspensions. The authors have proposed a suspension comprising a pneumatic system capable of changing the stiffness of the suspension and a semi-active magnetorheological damper capable of controlling the suspension damping. Eight configurations of this magnetorheological/pneumatic suspension result from combining two possible stiffnesses (compliant and stiff) and four possible means of producing damping (constant low, constant high, on-off skyhook control and on-off balance control). The minimization of a cost function, which considers both ride comfort and handling, leads to decision maps which indicate the most appropriate configuration depending on vehicle velocity and two pieces of information about the road: the international roughness index and the curve radius. All this information can be gathered from a GPS system and toggling between set-ups is fast, efficient, and easily done by simply opening or closing pipes in the pneumatic system and modifying the current supply in the magnetorheological dampers. The proposed magnetorheological/pneumatic suspension achieves the same roll angle levels as in a comparable passive vehicle while improving ride comfort by reducing acceleration by up to 30%.

Comparison of Minimum Detectable Crack Size in a Geared System From Three Different Vibration Transducer Types

Acoustic and vibration signals contain distinctive patterns useful for detecting defects in machinery. A number of signal processing strategies have been proposed for detecting and quantifying incipient defects in gears. Nonintrusive measurement techniques like those based on laser Doppler vibrometry (LDV) and microphones need to be studied in order to help users in selecting the appropriate transducer according to the application. This article presents an experimental design to determine, as a novel contribution, the minimum detectable crack size in a geared system comparing three different transducers: a microphone, an accelerometer, and an LDV. The comparison intends to discriminate the three transducers with respect to its early detection capability. Experiments were conducted in a closed loop torque test rig for several torque levels and speeds. Experimental factorial design was used to determine the main effects and their interactions in the detection process. The well-known Hilbert and wavelet transforms have been used as signal processing technique. Their advantages in the detection of incipient defects are highlighted in this article. The results indicate that the acoustic signal stands out as the method that first detects an incipient progressive crack in gears (it detected 1.3-mm-long cracks), although, as a drawback, the results obtained using the microphone signal are more sensitive to speed and torque. The second place was for LDV with 1.8-mm crack detection, and the third place for the accelerometer with 2.3-mm crack detection.

An adaptive pneumatic system for the attenuation of random vibrations

Adaptive suspensions can modify their filtering capacity to better accommodate excitations with different characteristics. The modification of stiffness (and, to a certain extent, damping) is particularly simple in pneumatic systems. The authors have proposed, modeled, analyzed, validated and tested a pneumatic suspension (composed of an air spring, an auxiliary tank and several connecting pipes) the transfer function of which can be modified simply by routing the air flow through the desired pipe. The method has been successfully tested in the case of unbalanced machinery. Procedures to estimate the input frequency have also been proposed for more general cases, but the question remains as to whether the adaptive scheme could be useful in the case of random excitations composed of a sizable range of frequencies. The focus of the work presented in this paper is to shed some light on this question. To this end, a suspension prototype is subjected to random inputs where the frequency content is tuned to increase the relative ‘weight’ of low frequencies, high frequencies or intermediate frequencies. The responses obtained using three different passive configurations, as well as an adaptive approach that can continuously choose among all three, are simulated, tested and compared. It will be shown that adaptation can minimize the root mean square displacement of the random response even in cases where there is significant overlap in the frequency content of the different types of input.

An Automatic Filtering Procedure for Processing Biomechanical Kinematic Signals

In biomechanics studies it is necessary to obtain acceleration of certain parts of the body in order to perform dynamical analysis. The motion capture systems introduce systematic measurement errors that appear in the form of high-frequency noise in recorded displacement signals. The noise is dramatically amplified when differentiating displacements to obtain velocities and accelerations. To avoid this phenomenon it is necessary to smooth the displacement signal prior to differentiation. The use of Singular Spectrum Analysis (SSA) is presented in this paper as an alternative to traditional digital filtering methods. SSA decomposes original time series into a number of additive time series each of which can be easily identified as being part of the modulated signal, or as being part of the random noise. An automatic filtering procedure based in SSA is presented in this work. The procedure is applied to two signals to demonstrate its performance.

An Example of Inquiry-Based Learning for Undergraduate Mechanical Vibrations

Laboratory or practical work is considered a crucial learning component for students of science and technology. It will be argued in this paper that the trend for inquiry-based learning that is beginning to percolate through classroom teaching can be brought to the design of laboratory tests. A project based on the free vibration of a one-degree-of-freedom pendulum serves as an example to show the integration of guided inquiry-based learning in a mechanical engineering curriculum. The goal is to design a pendulum system with a certain frequency of vibration and the challenge is to do it with specific elements and restrictions which, as the student needs to find out, do not lead to a solution just based on selecting a suitable pendulum length. In this laboratory teaching session, students were required to: identify the problem, model the system, derive governing equations, simulate, design, build, test, evaluate and share the solution. They are also required to experimentally measure the natural frequency and damping ratio of the system they built and adjust models and simulations accordingly. On the other hand, the session involves, albeit simplified, many of the common activities that the practicing mechanical engineer undertakes: design, develop, manufacture, assemble and test mechanical devices, including tools, engines, and machines.