Vibration Analysis and Mitigation Research

The majority of the research in the area of windscreen wipers concerns the vibrations in the system. This research can further be split into modelling, measurement and reduction through control techniques or mechanical design. In 2000, a paper called “Dynamic Analysis of Blade Reversal Behavior in a Windshield Wiper System” [29] was published which developed a highly accurate three dimensional model of the wiper

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system’s linkages, arms and blades. The purpose was to analytically investigate the causes of reversal noise (the noise caused by vibrations when the blade reverses its direction) and investigate ways to reduce it. The paper found that the angles and clearances between the wiper rubber and the blade had a large effect on the reversal noise, but also on other sources of noise in the system. The model is a complex multibody dynamic model which is not suitable for real time simulation and models behaviour that is not significant for the model to be developed in this project. Two later papers with shared authors to [29] used a similar model to investigate and mitigate squeal noise2 in the wiper system [30] [31]. Both papers used measurements, FEA and mathematical models to investigate the noise. They concluded that it could be reduced by changing the configuration of the wiper (as in [29]), material choice and surface treatment. The three papers clearly show that multibody dynamic modelling is capable of modelling the wiper system to a higher fidelity than is needed in this project.

In 2002, chatter vibrations3 were investigated in the paper “Simulation of Chatter Vibrations for Wiper Systems” [32] using a similar technique to the previous papers discussed. A mathematical model was developed and validated with real data to determine the factors affecting chatter vibrations. It was found, as in [31] [30] and [29], that the geometry of the blade and the rubber material had the biggest impact. Chatter vibrations were also investigated in [33] which used a validated finite element model to accurately simulate the system. Instabilities in the system that caused the chatter vibrations were then found using a complex eigenvalue method. The paper then proposes structural modifications to mitigate such vibrations.

A common method used to reduce friction induced vibrations is input shaping control. Input shaping is a control technique used to remove vibrations by combining impulse

2 _{Defined as the high frequency vibration of the wiper system (around 1000 Hz)} 3

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signals, designed to cancel vibrations, with the normal input command. In a 2008 paper called “Application of Input Shaping Control Strategy for Reducing Chatter Noise in the Automotive Wiper System” [34], the model developed in [29] was used to design an input shaping control system to reduce chatter noise. The vibrations that caused chatter were reduced by 30%. A paper released in 2010 with some shared authors with [34] follows a similar approach to [34] in order to use input shaping to reduce reversal vibrations with the same results (i.e. 30% decrease in vibrations) [35]. Similarly, in [36], input shaping is used to reduce unwanted vibrations. In this case, a particle swarm optimisation algorithm was used to time and shape the impulses in order to optimise the controller. Reduced vibrations were observed. Finally, in a paper entitled “Practical multi-objective controller for preventing noise and vibration in an automobile wiper system” [37], unwanted vibrations were reduced using input shaping, whose impulses were optimised using a Genetic Algorithm (GA). The model proposed in [29] was used to generate I/O data to train a recursive Artificial Neural Network (ANN) which was then implemented in the control system. A similar technique is used in this thesis to produce a real-time capable model. A collective weakness of these papers is that none of them implement the input shaping control in a real system, which will be driven by a wiper motor with its own dynamics. In reality, achieving an accurate target velocity is difficult to accomplish (see Chapter 7).

Other papers investigating vibration in wiper systems include [38] and [39], which specifically concentrate on how friction induces vibration using models and experimental measurements. Paper [38] concluded that squeal noise could be explained and modelled using the Stribeck friction effect. Paper [39] concurs with this, demonstrating that it is the negative friction-velocity curve at low velocities that causes the instabilities. Paper [40] takes experimental measurements of friction induced vibrations using microphones. The paper concluded that the wetness of the windscreen directly affected the amplitude and position (with respect to the wipe angle) of the vibrations. Note that [40] used the “Wet”,

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“Dry” and “Half-Dry/Tacky” windscreen conditions that are used in this project. The chaotic modelling and control of the wiper system have been studied by Chang and Lin in [41] and Chang in [42]. These papers serve to demonstrate how complex the behaviour of a wiper system can get, but are out of the scope if this project.

In general, the papers researching the vibrational behaviour and control of a wiper system present models that are too complicated to be used in this project, but do serve as a useful tool for understanding the behaviour of a wiper system and as starting points for simpler models. A general weakness in most vibration based papers is that they do not take into account the wiper motor, and thus are ignoring an integral part of the system which has an effect on the dynamics and the potential control solutions.