In this paper, an alternative gain-scheduled PID tuning procedure is proposed for gantry crane control systems. In order to avoid excessive overshoot and aggressive control action due to the proportional kick and/or derivative kick effects, an I-PD+PD type control law is considered. The scheduling parameter is considered the cable length due to the payload lifting and lowering movements. A linear parameter-varying (LPV) gantry crane model is constructed to enable gain-scheduled controller design with a linear matrix inequalities (LMIs) framework. Based on the LPV model, a convex optimization problem is formulized to minimize L2 gain under regional pole location constraints. Then, a fixed gain L2 gain state feedback I-PD+PD type controller and a conventional pole placement state feedback I-PD+PD controller are designed to investigate the efficiency of the proposed controller. A pole placement controller is tuned to minimize the very common ITAE (integral of time multiplied by absolute error) performance index. Simulation results show that the proposed controller has superior tracking performance under time-varying cable length, when compared with nominal fixed gain controllers.
Over 1 million core-needle breast biopsies are performed every year in the US alone [1], while gastrointestinal and prostate biopsies are estimated in similar numbers. The cost of core-needle breast biopsies ranges between $500 for manual procedures to $6,000 for image-guided procedures [2]. A retrospective study indicated that approximately 2.5% of breast biopsies fail [3]. Needle bending has been identified as a significant cause of error in biopsies and is particularly likely to occur at the insertion stage [2]. The associated risks include: i) biopsy of the wrong site leading to misdiagnosis; ii) puncture of sensitive areas in proximity of the insertion path; iii) repeated insertions, thus longer procedure du- ration and increased patient discomfort. Biopsy needles are also prone to buckling, which can damage the needle permanently. Common techniques for correcting needle bending in clinical settings include repeating the inser- tion (which can be time-consuming) or using a needle guide (which reduces the maximum insertion depth). In research, axial rotation is typically employed for steering bevel-tip needles, but it is less effective for needles with an axial-symmetric tip [4]. Additionally, straight insertions require continuous axial rotation, which can damage soft tissue due to the spinning of the bevel tip [5]. Alternative approaches employ steerable needles, which are not yet part of clinical practice [6]. We have developed a mechanical device that detects needle bending as soon as it occurs and that immediately reduces the insertion force thus helping to avoid deep insertions with deflected needles and the associated risks. Unlike existing solutions, our design does not require actuators or sensors hence it can be made MRI- safe, sterilisable or disposable. Finally, our device can be used with a variety of standard needles, including multi-bevel needles (e.g. diamond tip or conical tip).
In recent years, steerable needles have attracted significant interest in relation to minimally invasive surgery (MIS). Specifically, the flexible, programmable bevel-tip needle (PBN) concept was successfully demonstrated in vivo in an evaluation of the feasibility of convection-enhanced delivery (CED) for chemotherapeutics within the ovine model with a 2.5 mm PBN prototype. However, further size reductions are necessary for other diagnostic and therapeutic procedures and drug delivery operations involving deep-seated tissue structures. Since PBNs have a complex cross-section geometry, standard production methods, such as extrusion, fail, as the outer diameter is reduced further. This paper presents our first attempt to demonstrate a new manufacturing method for PBNs that employs thermal drawing technology. Experimental characterisation tests were performed for the 2.5 mm PBN and the new 1.3 mm thermally drawn (TD) PBN prototype described here. The results show that thermal drawing presents a significant advantage in miniaturising complex needle structures. However, the steering behaviour was affected due to the choice of material in this first attempt, a limitation which will be addressed in future work.
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