arXiv subjects

Lulu Cheng

Publications and source records attributed to Lulu Cheng.

8 recordsLinked to original sources

arXiv2024

Stochastic Multi-objective Multi-trip AMR Routing Problem with Time Windows

In recent years, with the rapidly aging population, alleviating the pressure on medical staff has become a critical issue. To improve the work efficiency of medical staff and reduce the risk of infection, we consider the multi-trip autonomous mobile robot (AMR) routing problem with the stochastic environment to find the solution to minimizing the total expected operating cost and maximizing the total service quality of patients so that each route violates the vehicle capacity and the time window with only a very small probability. The travel time of AMRs is stochastic affected by the surrounding environment, the demand for each ward is unknown until the AMR reaches the ward, and the service time is linearly related to the actual demand. We develop a population-based tabu search algorithm (PTS) that combines the genetic algorithm with the tabu search algorithm to solve the problem. Extensive numerical experiments were conducted on the modified Solomon instances to show that the PTS algorithm the efficient and reveals the impacts of the confidence level on the optimal solution, providing insights for the decision-maker to devise delivery schemes that trade-off the operating cost for patient satisfaction.

math.OC↗

arXiv2023

Order picking efficiency: A scattered storage and clustered allocation strategy in automated drug dispensing systems

In the smart hospital, optimizing prescription order fulfilment processes in outpatient pharmacies is crucial. A promising device, automated drug dispensing systems (ADDSs), has emerged to streamline these processes. These systems involve human order pickers who are assisted by ADDSs. The ADDS's robotic arm transports bins from storage locations to the input/output (I/O) points, while the pharmacist sorts the requested drugs from the bins at the I/O points. This paper focuses on coordinating the ADDS and the pharmacists to optimize the order-picking strategy. Another critical aspect of order-picking systems is the storage location assignment problem (SLAP), which determines the allocation of drugs to storage locations. In this study, we consider the ADDS as a smart warehouse and propose a two-stage scattered storage and clustered allocation (SSCA) strategy to optimize the SLAP for ADDSs. The first stage primarily adopts a scattered storage approach, and we develop a mathematical programming model to group drugs accordingly. In the second stage, we introduce a sequential alternating (SA) heuristic algorithm that takes into account the drug demand frequency and the correlation between drugs to cluster and locate them effectively. To evaluate the proposed SSCA strategy, we develop a double objective integer programming model for the order-picking problem in ADDSs to minimize the number of machines visited in prescription orders while maintaining the shortest average picking time of orders. The numerical results demonstrate that the proposed strategy can optimize the SLAP in ADDSs and improve significantly the order-picking efficiency of ADDSs in a human-robot cooperation environment.

stat.AP↗

arXiv2023

A Quick Response Algorithm for Dynamic Autonomous Mobile Robot Routing Problem with Time Windows

This paper investigates the optimization problem of scheduling autonomous mobile robots (AMRs) in hospital settings, considering dynamic requests with different priorities. The primary objective is to minimize the daily service cost by dynamically planning routes for the limited number of available AMRs. The total cost consists of AMR's purchase cost, transportation cost, delay penalty cost, and loss of denial of service. To address this problem, we have established a two-stage mathematical programming model. In the first stage, a tabu search algorithm is employed to plan prior routes for all known medical requests. The second stage involves planning for real-time received dynamic requests using the efficient insertion algorithm with decision rules, which enables quick response based on the time window and demand constraints of the dynamic requests. One of the main contributions of this study is to make resource allocation decisions based on the present number of service AMRs for dynamic requests with different priorities. Computational experiments using Lackner instances demonstrate the efficient insertion algorithm with decision rules is very fast and robust in solving the dynamic AMR routing problem with time windows and request priority. Additionally, we provide managerial insights concerning the AMR's safety stock settings, which can aid in decision-making processes.

math.OC↗

arXiv2023

The Multi-Trip Autonomous Mobile Robot Scheduling Problem with Time Windows in a Stochastic Environment at Smart Hospitals

Autonomous mobile robots (AMRs) play a crucial role in transportation and service tasks at hospitals, contributing to enhanced efficiency and meeting medical demands. This paper investigates the optimization problem of scheduling strategies for AMRs at smart hospitals, where the service and travel times of AMRs are stochastic. A stochastic mixed-integer programming model is formulated to minimize the total cost of the hospital by reducing the number of AMRs and travel distance while satisfying constraints such as AMR battery state of charge, AMR capacity, and time windows for medical requests. To address this objective, some properties of the solutions with time window constraints are identified. The variable neighborhood search (VNS) algorithm is adjusted by incorporating the properties of the AMR scheduling problem to solve the model. Experimental results demonstrate that VNS generates high-quality solutions. Both enhanced efficiency and the meeting of medical demands are achieved through intelligently arranging the driving routes of AMRs for both charging and service requests, resulting in substantial cost reductions for hospitals and enhanced utilization of medical resources.

cs.RO↗

arXiv2023

Stochastic scheduling of autonomous mobile robots at hospitals

This paper studies the scheduling of autonomous mobile robots (AMRs) at hospitals where the stochastic travel times and service times of AMRs are affected by the surrounding environment. The routes of AMRs are planned to minimize the daily cost of the hospital (including the AMR fixed cost, penalty cost of violating the time window, and transportation cost). To efficiently generate high-quality solutions, some properties are identified and incorporated into an improved tabu search (I-TS) algorithm for problem-solving. Experimental evaluations demonstrate that the I-TS algorithm outperforms existing methods by producing high-quality solutions. Based on the characteristics of healthcare requests and the AMR working environment, scheduling AMRs reasonably can effectively provide medical services, improve the utilization of medical resources, and reduce hospital costs.

cs.RO↗

arXiv2022

High Capacity Reversible Data Hiding in Encrypted 3D Mesh Models Based on Multi-MSB Prediction

As a new generation of digital media for covert transmission, three-dimension (3D) mesh models are frequently used and distributed on the network. Facing the huge massive of network data, it is urgent to study a method to protect and store this large amounts of data. In this paper, we proposed a high capacity reversible data hiding in encrypted 3D mesh models. This method divides the vertices of all 3D mesh into "embedded sets" and "prediction sets" based on the parity of the index. In addition, the multiple most significant bit (Multi-MSB) prediction reserved space is used to adaptively embed secret message, and the auxiliary information is compressed by arithmetic coding to further free up redundant space of the 3D mesh models. We use the majority voting system(MSV) principle to restore the original mesh model with high quality. The experimental results show that our method achieves a higher embedding capacity compared with state-of-the-art RDH-ED methods on 3D mesh models and can restore the original 3D mesh models with high quality.

cs.MM↗

arXiv2022

High Capacity Reversible Data Hiding for Encrypted 3D Mesh Models Based on Topology

Reversible data hiding in encrypted domain(RDH-ED) can not only protect the privacy of 3D mesh models and embed additional data, but also recover original models and extract additional data losslessly. However, due to the insufficient use of model topology, the existing methods have not achieved satisfactory results in terms of embedding capacity. To further improve the capacity, a RDH-ED method is proposed based on the topology of the 3D mesh models, which divides the vertices into two parts: embedding set and prediction set. And after integer mapping, the embedding ability of the embedding set is calculated by the prediction set. It is then passed to the data hider for embedding additional data. Finally, the additional data and the original models can be extracted and recovered respectively by the receiver with the correct keys. Experiments declare that compared with the existing methods, this method can obtain the highest embedding capacity.

cs.MM↗

arXiv2015

Hit and Run ARMS: Adaptive Rejection Metropolis Sampling with Hit and Run Random Direction

An algorithm for sampling from non-log-concave multivariate distributions is proposed, which improves the adaptive rejection Metropolis sampling (ARMS) algorithm by incorporating the hit and run sampling. It is not rare that the ARMS is trapped away from some subspace with significant probability in the support of the multivariate distribution. While the ARMS updates samples only in the directions that are parallel to dimensions, our proposed method, the hit and run ARMS (HARARMS), updates samples in arbitrary directions determined by the hit and run algorithm, which makes it almost not possible to be trapped in any isolated subspaces. The HARARMS performs the same as ARMS in a single dimension while more reliable in multidimensional spaces. Its performance is illustrated by a Bayesian free-knot spline regression example. We showed that it overcomes the well-known `lethargy' property and decisively find the global optimal number and locations of the knots of the spline function.

stat.CO↗