Cam Mechanisms Reverse Engineering Based on Evolutionary Algorithms

Cam follower mechanisms are widely used in automated manufacturing machinery to transform a rotary stationary motion into a more general required movement. Reverse engineering of cams has been studied, and some solutions based on different approaches have been identified in the literature. This article proposes an innovative method based on the use of an evolutionary algorithm for the identification of a law of motion that allows for approximating in the best way the motion or the sampled profile on the physical device. Starting from the acquired data, through a genetic algorithm, a representation of the movement (and therefore of the cam profile) is identified based on a type of motion law traditionally used for this purpose, i.e., the modified trapezoidal (better known as modified seven segments). With this method it is possible to estimate the coefficients of the parametric motion law, thus allowing the designer to further manipulate them according to the usual motion planning techniques. In a first phase, a study of the method based on simulations is carried out, considering sets of simulated experimental measures, obtained starting from different laws of motion, and verifying whether the developed genetic algorithm allows for identifying the original law or approximating one. For the computation of the objective function, the Euclidean norm and the Dynamic Time Warping (DTW) algorithm are compared. The performed analysis establishes in which situations each of them is more appropriate. Implementation of the method on experimental data validates its effectiveness.

Detachment Detection in Cam Follower System Due to Nonlinear Dynamics Phenomenon

The detachment between the cam and the follower was investigated for different cam speeds (N) and different internal distance of the follower guide from inside (I.D.). The detachment between the cam and the follower were detected using largest Lyapunov exponent parameter, power density function of Fast Fourier Transform (FFT), and Poincare’ maps due to the nonlinear dynamics phenomenon of the follower. The follower displacement and the contact force between the cam and the follower were used in the detection of the detachment heights. Multi-degrees of freedom (spring-damper-mass) systems at the very end of the follower were used to improve the dynamic performance and to reduce the detachment between the cam and the follower. Nonlinear response of the follower displacement was calculated at different cam speeds, different coefficient of restitution, different contact conditions, and different internal distance of the follower guide from inside. SolidWorks program was used in the numerical solution while high speed camera at the foreground of the OPTOTRAK 30/20 equipment was used to catch the follower position. The friction and impact were considered between the cam and the follower and between the follower and its guide. The peak of nonlinear response of the follower displacement was reduced to (15%, 32%, 45%, and 62%) after using multiple degrees of freedom systems.

Analysis of a Cam-Follower Mechanism for a Passive Parallel Lower Limb Exoskeleton

This project focused on the implementation of a novel cam-follower mechanism that was deemed to have good potential for practical application into a passive lower limb exoskeleton to determine its effectiveness in reducing the energy requirement of the user and its ability to match the walking gait of the user. The design of this novel-cam follower mechanism is inspired by the retractable mechanism of a ballpen. The cam follower mechanism was incorporated into a passive lower limb exoskeleton that was available prior to the study. Passive exoskeletons are intended to augment the load carrying capacity of the user through mechanical means instead of relying on external power. The walking gait study was conducted using physical testing. The mechanism was found to cause the user to bend below his natural centre of gravity a couple of times throughout the walking cycle. The user also had to stabilize himself from being rocked from side to side. Energy calculations were likewise conducted to investigate the energy consumption for a full cycle. The interchange among gravitational potential energy, spring potential energy and kinetic energy of the mechanism for a full walking cycle did not indicate possible advantage for the user.

Force Measurements Near a Natural Frequency of a Measurement System using Inverse Filters

Accurate time-resolved force measurements for complex experimental systems are important for minimizing erroneous and misleading data. These measurements become difficult when a natural frequency of the system is in or near the expected frequency domain of the time-varying force being applied. In the cases where it is not possible to avoid this occurrence, the experimenter typically abandons the setup. This work presents an inverse filter method to compensate for the dynamic response of the measurement system. A two degree-of-freedom measurement system is used to obtain force measurements with dominant forcing frequencies above and below the first natural frequency of the system. The results show that inverse filtering can be used along with digital low pass filters to correct amplification and phase shift due to the dynamic response of the measurement system to within ±4.0% of total forcing amplitude and ±5.0°. A simple cam follower mechanism is proposed as a method of low-frequency dynamic testing.

Reuleaux Triangle—Based Two Degrees of Freedom Bipedal Robot

This paper presents the design, modeling, analysis, and experimental results of a novel bipedal robotic system that utilizes two interconnected single degree-of-freedom (DOF) leg mechanisms to produce stable forward locomotion and steering. The single DOF leg is actuated via a Reuleaux triangle cam-follower mechanism to produce a constant body height foot trajectory. Kinematic analysis and dimension selection of the Reuleaux triangle mechanism is conducted first to generate the desired step height and step length. Leg sequencing is then designed to allow the robot to maintain a constant body height and forward walking velocity. Dynamic simulations and experiments are conducted to evaluate the walking and steering performance. The results show that the robot is able to control its body orientation, maintain a constant body height, and achieve quasi-static locomotion stability.

Development of experimental vibro-acoustic transfer function for a system with combined rolling-sliding motion

Combined rolling-sliding contact is present in popular non-linear systems such as cam-follower, gears, clutches, and brakes. These systems produce significant noise due to complex contact between the components during operation. The noise generated is a strong function of the contact parameters and excitation to the system. The objective of this study is to develop a transfer function to quantify the vibro-acoustic noise for various contact conditions. Acceleration, reaction forces, and acoustic pressure measurements are made on a cam-follower setup with combined rolling-sliding contact. Experiments are performed under different conditions of friction, lubrication, load, and speed. Contact forces are back-calculated using the kinematics. The transfer function relating the acoustic pressure to different forces is estimated. It is observed that the contact parameters govern the transfer function and hence the vibro-acoustic systems. The developed transfer function is useful in designing better sub-systems with combined rolling-sliding contact to reduce noise exposure, as a direct technique to relate the contact parameters to the noise does not exist. This study can be extended to other complex systems such as gears and clutches.