Abstract
In recent years, cities worldwide have become more and more congested. More than half of the world’s current population is now living in urban areas and this is expected to rise to 66% by 2050 as stated in a United Nations recent report. An overall urban migration is adding to the current environmental issues such as congestion and air pollution. There is now an increased demand for goods in urban areas resulting in logistical challenges. The freight industry is looking towards overcoming these economic and environmental challenges by relying on smart engineering solutions that are sustainable in the long term. With increased population density, businesses and residents now rely heavily on goods transportation on a more frequent basis than before. The frequency and volume of goods delivery are now adding a considerable amount of load on the ever-increasing road traffic and parking spaces in dense urban city centres where most of these businesses are located. Urban lifestyle is rapidly changing with on-demand next day deliveries and the current e-commerce online shopping paradigm. In the current sustainable urban logistics landscape, cargo bikes have shown to have more potential than other proposed costly and untried technologies such as drones or autonomous robots etc.Using a combination of a simple bicycle and a powered four-wheel electric trailer, mechanically guided and virtually coupled, higher volumes of parcel delivery is proposed in this thesis. The main challenges posed in this configuration of bicycle and trailer are the space-sensing technique, coupling mechanism and the electric powertrain for the smart electric trailer. This research focused on the development of a robust embedded control system in order to achieve a net neutral state between a bicycle and a load-bearing electric trailer combined to form an Electric Cargo Bike (ECB). This development utilised a powertrain based around a sensored Brushless DC motor with trapezoidal back-emf. Within proximity of each other and the ability to track the dynamic trajectory path produced by the bicycle rider, this net neutral configuration can be classed as a Hybrid Convoy System (HCS) or an eTrailer. The coupling of the bicycle and the electric trailer is based on the implementation of a novel sensing arm which registers the dynamic pedalling behaviour of the rider through a displacement sensor. Developing this sensing technique into a robust electromechanical coupling device allowed the implementation of a position based net neutral control system. The stability of this closed-loop system is achieved through multi-stage distributed digital controller deployment and tuning using both empirical and modelling approach.
In order to achieve a rapid response from the Net Neutral Position (NNP) controller, an electric powertrain based around a Brushless DC motor is integrated within a four-wheel trailer chassis based around Electrically Assisted Pedal Cycle (EAPC) regulations. In this thesis, the controller selection, development, tuning and deployment is presented and accurately supported by an extensive test campaign using 800W, 250W and 250W+250W powertrains in order to characterise the most suitable powertrain allowable within EAPC regulations. As a result of using an expansive empirical investigation methodology, the spacing error is minimised within a short range of sensor arm movement (setpoint) using ±380mm, ±150mm and ±190mm displacement sensors. This net neutral spacing, 𝑥𝑠𝑠, is then maintained throughout the bicycle and trailer operation regardless of the parcel weight (torque disturbance rejection) present on the trailer or the acceleration (maximum allowable power) produced by the rider. Prior to finalising the commercial prototype, these powertrain and spacing arrangements were tested on two, three and four-wheeled trailers.
The successful deployment and empirically optimised parameters of the distributed controllers, allows the bicycle rider to experience a net neutral load effect. This means zero load is experienced by the rider while delivering parcels weighing up to 250kg, loaded on to the coupled trailer running at a maximum speed of 8.5mph or 13.68kph. Additionally, the developed NNP control system is integrated on an embedded microcontroller-based platform enabling a configurable working prototype to be tested infield. Numerous real-time tests were carried out in order to tune and optimize the control system response for varying load and gradient conditions, before commencing commercial testing of the Electric Cargo Bike at Outspoken Delivery in Cambridge and UPS cargo depot facilities in Camden Town, London.
As a result of this novel engineering solution, operations within city logistics will provide an overall improvement in the urban environment through overcoming congestion problems in dense urban areas, improvement in air quality, providing better road safety, enhanced mobility and greater access to residents and businesses creating a healthier and better eco-system for an e-commerce driven society.
| Date of Award | 28 Apr 2021 |
|---|---|
| Original language | English |
| Supervisor | Simon Iwnicki (Main Supervisor) & Roger Goodall (Co-Supervisor) |