Robotics Lab

Department of Communications
and Information Engineering

University of Murcia

 
The MIMICS project 
 

(Click on any image to enlarge it)

Introduction

The aim of the MIMICS project is to develop an intelligent platoon of vehicles, where the leading vehicle (which is manned) acts as a guide for the following vehicles (which are unmanned). For practical reasons the real prototype has been limited to only two cars (Figure 1). The operation of the leading car is quite simple: it uses its sensors to send information to the following car, which then uses both its sensors and the information received to control the actuators. All the information is shared using wireless links. The autonomous vehicle built for this project is called SatAnt.


Figure 1. Model of the MIMICS convoy

The system is intended to be deployed in special roads with controlled traffic. For instance the scenario can be a goods delivery application in an industrial area, where a good GPS coverage is possible and also the velocities are not high. For the rest of this section this scenario is assumed.

 

The SatAnt Vehicle

The SatAnt vehicle (Figure 2) is based on a COMARTH S1-50 two-seats sport car, which has been heavily modified  to allow it to be controlled by a computer based system. The weight of the whole vehicle is 700 Kg and the engine provides 90 h.p. which gives a high power to weight ratio and allows high accelerations. The modifications include an automatic gearbox, electronic assisted steering system, electronic speed control, and electronic braking system. For safety reasons, all electronic systems have been designed in such way that they allow both manual and automatic control, and at any time the electronic systems can be disengaged. Both the frame and the outer shell have been modified to accommodate for the non standard equipment (Figure 3).
 

Figure 2. The SatAnt vehicle


Figure 3. Vehicle frame and mock-up of the electronics

The modified car has a different set-up of the control panels with respect to the production car. The main differences (Figure 4) are the automatic gearbox, a set of voltage meters, a safety switch, and a LCD panel to interact with the control software and the navigation aids.


Figure 4. Vehicle dashboard

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Vehicle Electronics

The leading car is provided with a portable equipment that contains the positioning sensors, a small  processing unit and the radio communication link (Figure 5). This portable system can be used in any standard car.


Figure 5. Leading car electronics (portable rack)

The SatAnt vehicle is far more complex. It is automated to allow a computer to fully control it (Figure 6). Next, it includes enough processing elements and sensors to perform autonomous tasks.


Figure 6. SatAnt vehicle electronics (onboard rack)

The SatAnt sensors system (Figure 7) includes a Novatel GPS (which provides global positioning data), a Precision Navigation electronic compass (which provides both heading and pitch/roll data), relative encoders attached to the four wheels (which provide vehicle speed), absolute encoder attached to the steering wheels arm (which provides steering wheels angle), and a Fujitsu  77 GHz radar (for detecting obstacles and the leading car). An important feature of the GPS unit is that it makes use of the Euro Geostationary Navigation Overlay Service (EGNOS), the European implementation of the Wide Area Augmentation System (WAAS). WAAS is a system of satellites and ground stations that provide GPS signal corrections, giving a much better position accuracy.


Figure 7. SatAnt onboard sensors (radar, compass, wheel encoder)

The hardware architecture (Figure 8) has been organised in two layers, in which low level controllers and electronics (microcontrollers)  communicate trough a CAN bus operating at 500 Kbs, and high level electronics (microprocessors) communicate through an  ethernet bus operating at 100 Mbs. The design goals for the hardware architecture were modularity and scalability, in such a way that adding a new module does not interfere with the existing ones. One advantage of this organisation is the use of standard buses, and in particular using the same standard bus used in the automotive sector.


Figure 8. SatAnt hardware architecture


The electronic speed control system (Figure 9) consists on four different elements: the throttle pedal sensor, the servo actuated injector, the servo controller, and the speed controller. The servo controller and the speed controller are connected through the CAN bus.


Figure 9. Electronic speed control system

The speed controller is a hierarchical fuzzy controller (Figure 10) that uses both the wheel encoders and road steepness information to decide the position of the injection servo in order to maintain a commanded speed. Given the available engine power and the light weight of the whole vehicle, the plant presents high non-linearities. In particular, controlling both acceleration and deceleration are important issues. Thus, there are three basic controllers: one for uphill control, one for downhill control and the other for in level control. The selection of the active controller is performed by a high level controller whose input is the pitch/roll data. Depending on the values a combination of the basic controllers is executed. The output of the pitch/roll sensor used is quite noisy and a fuzzy IIR filter is applied to the sensor in order to smooth the signal. The servo controller receives both the throttle pedal sensor signal and  the speed controller output and actuates the servo position accordingly. In the case that the throttle is actuated by a human operator, the manual input takes control over in any condition. All the electronics for both the servo control and speed control have been custom designed.


Figure 10. Fuzzy logic speed controller

The electronic braking system (Figure 11) consists on the pedal actuator, a Maxon motor controller and the braking controller. The pedal actuator is a complex mechanical structure  that allows parallel actuation of the pedal for both the human operator and the braking motor. The braking controller is in charge of applying braking patterns by sending signals to the motor controller through the CAN bus.


Figure 11. Electronic braking system

A braking pattern (Figure 12) is composed of three parameters: motor pressing time (to control the pressure applied to the brakes), motor standby time (to control how much time the brake is kept pressed), and motor releasing time (to control how fast the brake is released). Both the braking controller electronics and the mechanical structure have been custom designed and built.


Figure 12. Braking automata

The electronic steering system (Figure 13) consists on a Delphi power steering column and a steering controller. The power steering column is directly attached to the steering controller. It includes a switch to engage or disengage the automatic control.


Figure 13. Electronic steering system

The steering controller is a fuzzy controller (Figure 14) that uses the steering column absolute position sensor to maintain a given wheel angle. The steering controller has been custom designed.


Figure 14. Fuzzy logic steering controller

Application

The MIMICS application, which is the actual software implementation of the MIMICS system, runs on the high-level layer of the hardware architecture of the SatAnt vehicle. It relies on the ThinkingCap-II architecture applied to a multi-robot scenario. As such, it consists of four different types of elements:

  • Multi-robot Server. Given the nature of the communication infrastructure of the TC-II, all the information shared by the different elements is exchanged through and stored in a multi-robot  Linda space. There should be only one instance of this element.  
  • Manned Vehicle. This is the element that will serve as a guide for all the autonomous vehicles. There  should be only one instance of this element. Although it is out of the scope of the project, extending the application to support more than one manned vehicle is quite simple.
  • Unmanned Vehicle. This is the element that will follow a leading vehicle, whose identifier is a priori set by the system designer. This element implements all the high level control software, including path-planning, obstacle avoidance (Figure 15), localisation, behaviour control, etc. It is possible to have more than one instance of this element.

Figure 15. Obstacle detection and avoidance
  • Monitor. For monitoring purposes it is possible to receive all the information received at the information server, for instance the state of the convoy (Figure 16). The monitor element displays this information and allows the operator of the system changing some parameters (Figure 17) and monitoring the internal state of the different elements (Figure 18). It is possible to have more than one instance of this element.


Figure 16. Convoy navigation monitor


Figure 17. Teleoperation and control panel


Figure 18. Device management (compass and GPS)
Videos

The following video shows the state of the MIMICS project during summer 2001. In those dates the SatAnts vehicle only incorporated an Intelligent Cruise Control (ICC), which allows maintaining a given speed (that of the leading vehicle) and in the case of detecting a possible collisions (using the equipped radar) the vehicle is stopped. Most of the takes are from a race circuit (Fuente Alamo, Murcia, Spain) closed to normal traffic.
The following video shows the SatAnt vehicle during some autonomous driving tests. The paths have been previously recorded using the leading car. Some of the takes are from a large parking lot of the Campus and the others are from the Campus road, open to normal traffic.

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Last updated on February 24, 2004
humberto@um.es