Automated robot-based charging system for electric vehicles

Abstract

With the rising number of electric and hybrid vehicles the demand for customer-friendly and innovative solutions for the charging infrastructure is growing steadily. Furthermore, future autonomous driving and parking vehicles are calling for new ap-proaches regarding to battery charging. Nowadays electric vehicles have to be charged by hand. In other words, someone has to connect the charging cable with the charging socket of the vehicle. This paper deals with automated charging systems for electric vehicles. In order to realize tethered charging a fully automated system supports the complete process. The first part of work explains advantages of automated conductive charging systems regarding to other automated concepts and why such systems are needed. The second part deals with an investigation of the state of art. Thereby it is evidenced which systems are already developed and published. Afterwards, challeng-es and problems behind automated conductive systems are shown. Thereby the indi-vidual problems are analysed and illustrated. Finally, an initial concept for automated charging station is presented and discussed as a solution charging multiple and vari-ous types of vehicles at public parking facilities.

Full text

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Automated robot-based charging system for
electric vehicles
Bernhard Walzel*, Christopher Sturm, Jürgen Fabian, Mario Hirz
Institute of Automotive Engineering

Automated robot-based charging system for electric vehicles
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Abstract
With the rising number of electric and hybrid vehicles the demand for customer-
friendly and innovative solutions for the charging infrastructure is growing steadily.
Furthermore, future autonomous driving and parking vehicles are calling for new ap-
proaches regarding to battery charging. Nowadays electric vehicles have to be charged
by hand. In other words, someone has to connect the charging cable with the charging
socket of the vehicle. This paper deals with automated charging systems for electric
vehicles. In order to realize tethered charging a fully automated system supports the
complete process. The first part of work explains advantages of automated conductive
charging systems regarding to other automated concepts and why such systems are
needed. The second part deals with an investigation of the state of art. Thereby it is
evidenced which systems are already developed and published. Afterwards, challeng-
es and problems behind automated conductive systems are shown. Thereby the indi-
vidual problems are analysed and illustrated. Finally, an initial concept for automated
charging station is presented and discussed as a solution charging multiple and vari-
ous types of vehicles at public parking facilities.

Automated robot-based charging system for electric vehicles
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1. Introduction
Besides the limited range of electric vehicles in comparison to conventional powered
vehicles, one additional drawback is the time consuming and laborious charging pro-
cess. To enable comfortable and autonomous battery charging lot development effort
is invested in inductive charging systems. Due to the advantages of the contactless
method, manufactures are working on the marketability of this technique. But several
challenges like energy losses, electromagnetic radiation, complex vehicle adaption or
environmental impacts on humans and animals still have to be solved. Furthermore,
long driving ranges together with short charging intervals are essential for a high cus-
tomer benefit. Due to a significantly lower power transmission performance, high
charging capacities are not feasible with inductive systems, but only with conductive
systems (DC quick or fast charging). Battery switch stations provide another option.
Because of the high investment costs as well as the difficult grid and vehicle integra-
tion these techniques will be not discussed further here. Figure 1 depicts how many
kilometres per hour loading capacity can be covered depending on the loading method
[1, 2] and based on the energy consumption of an average electric vehicle [3]. In this
comparison, charge and discharge losses are not considered. As shown fast charging
technologies with loading capacities up to 170 kW [2] reduce the charging time sig-
nificantly in comparison to low charging methods.
Figure 1: Charging capacity by charging method
In order to realize powerful DC charging currents the wire diameter must grow. This
in turn makes the cable heavy, stiff and unhandily, so that people might have prob-
lems to charge their vehicle [4]. This possibility to load vehicles as user friendly as

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possible is one reason why automated conductive charging systems are getting in-
creasingly interesting.
Autonomous vehicles together with automated charging systems offer new opportuni-
ties. Fully automated park and charging solutions enable customer-friendly and inno-
vative service concepts. For example, driver parks in front of shopping centres: The
car drives to the next free parking lot autonomously, charges the batteries automatical-
ly and picks up the driver after the shopping tour by a call via mobile phone app.
Volkswagen works already on the realization of similar projects with automated cars
and inductive charging systems [5].
2. State of the art
Automated charging systems are in development this time, but no manufacturer has
launched a series product on the market until now. Furthermore, every current pub-
lished system is only customized for one specific vehicle model. That means that only
that specific model can be charged. In future years an automated system should be
able to charge every electric vehicle independent from the car type.
2.1 Volkswagen e-smartConnect
The manufacturer VW recently presented such a system for an e-Golf, as a research
facility in the test phase. The project, shown in Figure 2, is called e-smartConnect and
is based on a KUKA LBR iiwa, a Robot of the newest generation. The DC quick
charging process starts with a communication between vehicle and electric filling sta-
tion. The vehicle transmits its data to the charging station, which transmits in return
the target position for the automated parking. The charging socket of the vehicle has
to be in a target area of 20 by 20 centimetres. Afterwards, a camera on the robot de-
tects the exact position of the charging socket, which is accurately defined to a milli-
metre. Following, the robot-gripper picks the DC-Connector and links it with the
charging socket of the vehicle. After having linked the DC-Connector, the charging
process starts. Once the battery is fully charged, the robot automatically unplugs the
DC-Connector [6].

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Figure 2: VW e-smartConnect [6]
2.2 Tesla charging-robot
The US Company Tesla also works on an automated system (Figure 3). Their concept
is even based on DC current and should load their on-site vehicles. The charging cov-
er opens automatically when the parked vehicle is ready for loading. The system de-
tects this and afterwards the snakelike prototype robot arm is searching its way to the
charging socket fully autonomously. Once the connection between the robot and the
vehicle is made, the charging process can be started. The idea behind the concept is,
that the driver does not have to get out of the car to charge the vehicle. The complete
loading procedure is applied by the robot. How the robot finds its target and detailed
technical information about the charging system are not published yet. In general, the
system is currently in a prototype status this time. A benefit of Tesla is that all their
cars have the same position of the charging socket and also the same charging plugs
[7].
Figure 3: Tesla charging robot [7]

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2.3 Charging system TU-Dortmund
The Technical University of Dortmund started a project named ALanE. The acronym
stands for automated charging system for sustainable electric mobility (Figure 4). The
aim of the project is to charge a parked electric vehicle without needing the driver to
plug in the charging cable. A manual intervention of the driver is not necessary. Thus,
in comparison to established charging systems, the ALanE system raises the comfort
enormously, which represents itself as a unique selling point in comparison to conven-
tional powered vehicles. The charging system of the TU Dortmund contains a stand-
ard energy supply and a wallbox, which is extended with a cost-effective and compact
connection module (VBM). The connection and disconnection process can be started
via a smartphone app. This system is also in a prototype status yet and under further
development [8].
Figure 4: Charging robot TU-Dortmund [8]
2.4 Charging system NRG-X
The NRG-X concept represents itself as the first fully automatic charging solution.
The fundamental idea was to create a system, which transfers high power energy for
fast charging, enables a great range of parking tolerance and substitutes an expensive
conventional wallbox. Additionally, it can be easily adapted to every electric vehicle.
The system shown in Figure 5 contains two basic components, a connection array,
which is mounted in the middle of the car underbody and a base station, which repre-
sents the connection system at the parking area.
The surface of the connection array is consistently structured by a hexagonal pattern,
whereas each cell has a conical shaped recess. The base station, which constitutes the
counterpart, slides into any cell by an orthogonal movement towards the connection
array. This means, any arbitrary position of the cone within the dimensions of the

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connecting array reaches a discrete final position in the middle of the respective con-
tacting cell. The positioning cone must be resilient and therefore laterally (in x- and y-
direction) moveable for the distance of a contacting cell outer radius.
The hole charging process is quite simple: When an electric vehicle, which is adapted
with the NRG-X connection array, approaches to a garage or parking space, the
NRG-X base station automatically starts to communicate with the connection array.
The only requirement is that the electric vehicle must contain a wireless module. It is
not necessary to park the vehicle in an exact predefined position. A position validation
system ensures the correct position where an automatic connection is feasible. After
the system checked the authorization and the batteries state of charge, the charging
process starts automatically. The NRG-X base station lifted upwards to the connection
array of the car underbody and connects the system. Possible charging power reaches
up to 22 kW. The charging process starts automatically when a secure connection is
enabled or can be scheduled manually or by an intelligent charging management sys-
tem. If the battery is completely full, the connection system disconnects immediately
and automatically. In a further expansion stage, direct current quick charging should
be realized above >100 kW [9].
3. Problem areas
The main idea of automated charging systems includes a very easy and comfortable
charging process. The car parks in the parking bay and the remaining steps are being
Figure 5: NRG-X [9]

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finished by the system automatically. That means the automated charging system de-
tects the type and model of car, recognises thereupon the position of the charging
socket, the required charging cable and charging strategy and starts afterwards with
the charging process. As soon as the process is finished, the system picks up the
charging cable and the vehicle is ready to drive. But there are some obstacles that
need to be adjusted in order to realize automated conductive charging. From a purely
technical point of view, such systems seem to be state of the art, but there are some
challenges that must be solved - and for the target to handle different vehicle types,
the challenges are rising significantly.
There is no standard for the position of the charging socket. An investigation of vari-
ous vehicle types shows big differences regarding the socket places depending on the
car brand and type. Electric and hybrid vehicles usually have their sockets on the right
or left side, additionally some cars have it on the front or back side of the vehicle. Fur-
thermore, the height of the socket is also different. There is a European standard for
charging cables, the Type 2 (Mennekes) connector, but many manufacturers, especial-
ly in Asia or USA use other connector types.
A second big problem can be found in the charging cap mechanism. Several vehicles
have a security cap that makes it impossible to charge the vehicle without removing
them. Even in this field there are differences. Some brands have a rubber plug which
has to be unscrewed, others have a plastic flap. The variety of the systems is often
simply based on specific design solutions.
The target to charge multiple vehicles and different vehicle types at parking facilities
requires complex devices for handling and management of cables, especially by the
use of DC quick charging. Long and heavy cables with limited bend radius waste a lot
of space and additionally, if they are not carried by the robot, separate logistic equip-
ment is needed. For example, the weight of a CCS-Type 2 charging cable for charging
capacities of up to 106,25 kW is 1,7 kg/m and it has an outer diameter of 28,2 mm
[10].
An overview about various vehicles types, charging sockets, plugs and security sys-
tems is presented in Figure 6 and 7. Figure 8 shows a typical parking situation of ve-
hicles including the resulting charging socket position. As mentioned, these varieties
of systems and vehicle-specific requirements complicate an automation of the charg-
ing process enormously.

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Figure 6: Examples for various vehicles types, charging sockets, plugs and security cap systems
[11, 12, 13]
Figure 7: Cable connector types [14]
Figure 8: Vehicle positions in parking lots,
resulting in different charging socket positions (red points)

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4. Concept proposal
As discussed in Section 2, several projects are already dealing with automated charg-
ing, but every concept either can charge only one specific car with one specific charg-
ing plug or is accompanied by costly vehicle adaptations. In this subsection, a concept
for public parking facilities is introduced (Figure 9). The concept proposal is capable
to charge any electric car independently from the brand, the charging socket position
or the vehicle parking lot position and it does not require complex vehicle adaptions
or modifications. Furthermore, it is possible to charge multiple vehicles with only one
robot.
The basis of the concept is a lightweight collaborative robot that is mounted on a
bridge crane-like system. This approach increases the range of motion for the robot
significantly - every charging station spot is reachable and the number of cars is only
limited by the length of the crane system. Safety plays an important role when using
robots. Safety features of the robot allow people to be in the same working area as the
robot and no safety fence is needed (collaborative robots). Force torque control ena-
bles well contact detection as a programmable resilience. Furthermore, the plug-in
process is precise and force sensitive. Companies like Universal Robots or KUKA of-
fer such robots [15, 16].
Every parking lot is equipped with a longitudinal movable and rotatable cable maga-
zine, which travels closely to the charging socket before the charging process begins.
This prevents sliding on the ground as well as difficult handling of heavy and long ca-
bles. With a universal gripper tool mounted on the robot arm, different types of charg-
ing plugs can be picked up from the cable magazine.
If a vehicle has to be charged, it parks in a free parking lot (manually or autonomous-
ly). For the next steps and for a successful charging process, the system must gather
important data, including information of the already discussed variety of systems in
the subsection problem areas. With wireless interconnectedness of vehicle, electric
filling station, mobile phone and web servers, the charging process can be started or
stopped as well as vehicle and charging strategy data can be transmitted and updated.
The easy integration of billing and payment applications and storing and evaluation of
the costumer charging behavior improves costumer benefit additionally. Figure 10
shows a proposal for the data communication and the data management of an auto-
mated electric filling station in public areas.
After the required information is transmitted, it is possible to control the charging
process and the battery’s state of charge. Meanwhile the vehicle is charging, the robot
can serve other vehicles that also need to be charged. When the charging process is

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finished, the robot disconnects the cables and puts it back into the magazine and the
whole process can start again from the beginning.
Figure 9: Proposal of an automated charging station for public areas
Figure 10: Data communication and data management proposal

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5. Discussion and Outlook
Conductive automated charging systems are a new emerging topic in the electric vehi-
cle industry. By increasing charging power, the cables are getting more unwieldy and
thereby charging of a vehicle can be very aggravating. Some pilot projects already
employ with automatic charging systems, but currently they are all in a prototype sta-
tus. The presented concept of an automated charging robot for parking garages gives
an overview of possibilities for possible solutions. It considers the importance that
every electric vehicle can be charged by one system. Furthermore, there are no modi-
fications to the vehicle necessary. Future electric cars will be designed for automated
charging. This includes barrier-free access to the charging socket or automated open-
ing and closing systems of the loading covers and standardized communication sys-
tems. Inductive charging systems will be an alternative, but disadvantages like the
limited charging capacity or unstandardized systems may restrict the application to
private sector usage. Conductive automated charging systems include a high potential,
whether in private or public sectors, to make charging of electric cars more comforta-
ble.

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