EUROPEAN COMMISSION

DG RESEARCH

SIXTH FRAMEWORK PROGRAMME

THEMATIC PRIORITY 4.3

FP6 – 2005 – Transport – 4

Specific Targeted Project– CONTRACT N. TST5-CT-2006-031360

PISa Powered Two Wheeler Integrated safety

Deliverable no. D29

Dissemination level Public

Task Package Task 4.5

Author(s) and Partner name Weijenberg, Pauwelussen, Oudenhuijzen, TNO

Co-author(s) and Partner name Pierini UNIFI, Grant VSRC

Status (F: final, D: draft) D29 – Final – v1.4 – February 2009

File Name D029 HMI for PTW rider assistance systems v1.4.doc

Project Start Date and Duration 01 May 2006 - 30 April 2011

Checked by WP leader Roland Schultz 25-02-2009

Approved by coordinator Ard de Ruiter 25-02-2009

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Executive Summary This document describes the results of task 4.5 ‘HMI (Human Machine Interface) and Warning strategies’. TNO, UNIFI, VSRC and Carver co-operated in this task. The HMI for PoweredTwo Wheelers (PTWs) was developed in this task based on the results from WP 2, 3, tasks 4.1, 4.2 and 4.3. This HMI assists the PTW rider to avoid accidents. Special attention was given not to distract the rider or unexpectedly take over control, which may lead to unintended extra danger for the rider.

Three topics were considered and worked out in detail for this task:

1. Autonomous braking: autonomous braking is considered in this project, the question we asked ourselves was: when and how autonomous braking systems may be applied?

2. Automated PTW rider Distance Support System (DSS): a system was developed (hard and software) to aid the rider in maintaining proper time headway in an intuitive manner. This resulted in an automated system, for which the rider is, however, still able to override the system and take over control when needed;

3. PTW rider warning devices and related warning signals

This report discusses the theoretical background behind PTW brake assist (BA), autonomous braking (AB), adaptive cruise control (ACC), distance support system (DSS) and related warning devices from an HMI point of view. Furthermore, the control algorithms for the DSS and its hard and software were specified in detail. Similarly, a specification was given for the tactile saddle, both in signal, electrical and hardware. This tactile saddle will be used as the warning device for the PISa project.

It is recommended, before any formal testing of the PISa test bike, to fine-tune the actuator control algorithm of the DSS. This system was tested for its functionality using a tabletop setting. Further fine-tuning is needed in order to provide the first test riders with a proper haptic feedback.

D029, HMI for PTW rider assistance systems 3

TABLE OF CONTENTS

1 Introduction 4

2 Human Machine Interface approach for PTWs 5

2.1 Brake Assist and Autonomous Braking systems 7

2.2 Adaptive Cruise Control and PTWs 7

2.3 Distance Support System development for PTWs 8

2.3.1 The baseline for the Distance Support System 8 2.3.2 Driving phases 8 2.3.3 Haptic feedback 10

3 Human Machine Interfaces specifications for PTWs 12

3.1 Distance Support System and haptic throttle HMI 12

3.1.1 The haptic feedback algorithm 12 3.1.2 Pilot experiment 1: Level of haptic force feedback 13 3.1.3 The Distance Support System algorithm 15

3.2 The Distance Support System hardware 18

3.2.1 Hardware for the actuator 19 3.2.2 Actuator control algorithm 21 3.2.3 Physical design and interfacing 22

3.3 The tactile saddle Human Machine Interface 22

3.3.1 Physical design 22 3.3.2 Electrical design 24 3.3.3 Signal design 24

4 Conclusions and recommendation 26

5 Sources 27

5.1 Reference List 27

6 Appendices 28

6.1 Appendix A 28

6.2 Appendix B 29

6.3 Appendix C 30

6.4 Appendix D 31

6.5 Appendix E 34

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1 Introduction

This document is one of a series on safety systems for Powered Two Wheelers (PTWs) and is one of many deliverables of the EU PISa project (PISa stands for Powered Two wheelers Ingetrated sAfety). This document describes the results of task 4.5 ‘HMI (Human Machine Interface) and Warning strategies’. TNO, UNIFI, VSRC and Carver co-operated in this task. The HMI for Powered Two Wheelers (PTWs) was developed in this task based on the results from WP 2, 3, tasks 4.1, 4.2 and 4.3. This HMI assists the PTW rider to avoid accidents. Special attention was given not to distract the rider or unexpectedly take over control, which may lead to unintended extra danger for the rider.

Three topics were considered and worked out in detail for task 4.5:

1. Autonomous braking: when or when not and how autonomous braking systems may be applied?

2. Automated PTW rider distance support system (DSS): a system was developed (hard and software) to aid the rider in maintaining proper time headway in an intuitive manner. This resulted in an automated system, for which the rider is, however, still able to override the system and take over control when needed;

3. PTW rider warning devices and related warning signals

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2 Human Machine Interface approach for PTWs

The baseline for this document is defined in Workpackage 2 and 3. In workpackage 2 accident analysis and user needs were analyzed to define system functions that have a large effect on PTW safety based on available technology and user acceptance (see PISa deliverables D12, D15 and D17). Additionally, system functions were defined using technology already available from the car industry. These systems were adapted for PTW use and integrated using the decision logic, a controlbox for various PTW safety systems, developed for PTW use as part of the PISa project. The relationships between the different aspects of the safety system development are schematically shown in Figure 1.

Figure 1 Project scheme illustrating the relations between scenarios, functions, systems and the HMI

It was decided, after considering the accident analysis and user needs, that the PISa partners focus on the functions and related systems specified in Table 1:

Table 1 The PISa functions, systems and the related HMI

Functions Systems (sub) HMI

Automatically slow/stop vehicle without rider input

Autonomous braking (AB) Warning the rider using a tactile saddle

PTW to detect other vehicle and provide warning (to PTW rider)

Sensing system

Improve PTW conspicuity Warnings (conspicuity) On/off switch of warning lights

Balance front to rear braking force

Brake assist: CBS (CBS = Combined Braking System (activating both front and rear wheel braking using only one of the two brake controls)

There is no need for an HMI in case the CBS works or at most a simple visual warning could be enough

Avoid locking wheels in straight line

Brake assist: ABS Warning system is taking over and/or dangerous situations:

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Amplify braking force Brake assist: combined braking system

(Warning) sign/visual display

Reduce closing speed/maintain distance

ACC/DSS (Distance Support System)

Haptic throttle

The systems support the rider under several potential dangerous situations. The integrated systems that will be developed in the PISa project are:

• An haptic throttle for car/PTW-following support (comparable with ACC);

• A brake system 1 (controlled by rider);

• A brake system 2 (controlled by decision logic);

• A (semi)active suspension for optimised braking distance.

The HMI interacts between the systems and the rider depending on the system and situations. These situations, the driving phases, were divided into (see Figure 2):

• a free-driving phase;

• a regulation phase;

• a reaction phase.

In the free-driving phase, there is no other traffic nearby. In the regulation phase, the rider is following a vehicle at a safe distance. In this situation, the rider could be supported in the vehicle-following task to maintain a safe distance. In the reaction phase the distance between a lead vehicle or an object is critical. The rider is not carrying out a vehicle-following (closed loop control) task anymore but has to avoid a collision (open loop) by braking or swerving. Depending on the phase, the systems support the rider or take over part of the control. It is important for the rider to know if (s)he or the system is in control. This has to be clear in the HMI design1.

The Brake Assist (BA), the Autonomous Braking System (AB), the ACC, the DSS and the warning devices will be discussed in the sections below.

Figure 2 Driving phases

1 It may appear in this situation that the system takes control overriding the rider. However, this is not completely true: the BA tries to interpret the riders intention, the AB needs rider input before activation.

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2.1 Brake Assist and Autonomous Braking systems

The brake assist (BA) is a system that amplifies braking force when the system senses that the rider initiates an emergency stop. It compensates for the potential danger that the full braking potential is not used even when initiating an emergency stop. The BA is successfully used in luxury cars: here the pedal activation speed and force is used to sense when a driver has the intention to make an emergency stop. The challenge for PTWs is that it is currently unknown what signals, from the rider, can be used to sense an intended emergency stop. This can only be investigated in life trials (these are planned for 2009 in the PISa project): hence, the BA will be investigated in more detail in the planned trials.

The following is known at this moment: the brake assist should only assist the rider amplifying brake force when the decision logic (DL) senses that the rider wants to make an emergency stop. Currently, it is not known what should be measured to be sure that the rider wants to make an emergency stop. As such, a brake assist cannot be implemented at this very moment. During planned test trial within the PISa project, for 2008, tests will be done to investigate which parameters can be measured to sense that the rider wants to make an emergency stop. It is possible to implement the BA once the parameters are known and when they seem feasible and safe.

The autonomous braking (AB) system is fed by the laser scanner and the decision logic and decelerates the PTW autonomously. The AB should only be activated after the PTW rider has been warned (about 0.25 – 0.35 seconds, allowing for latency time) using the tactile saddle and while the PTW is upright and not during cornering.

2.2 Adaptive Cruise Control and PTWs

Information relating to cruise control and ACC (Adaptive Cruise Control) systems, currently used on cars was used as a basis for PTWs. This information has been taken from the Deliverable D03 ‘Report summarising the knowledge, issues and techniques for the (PISa) project’. Information has been taken from the Internet relating to the Honda Safety Initiative research programme and ACC systems. A brief internet review of motorcycle models and motorcycle aftermarket systems has revealed that few make/models have cruise controls fitted as standard and a few have the possibility as an optional extra. These include the Honda Goldwing range, BMWs including the R1200RT, K1200GT and K1200LT and various Harley Davidsons. ACCs are not implemented on any commercially available PTWs.

The systems currently available, cruise controls, are systems designed for touring/cruising bikes, where long distances on motorways and highways, means that the possibility to set a constant speed is a desirable advantage in terms of comfort for the rider. As yet, little evidence has been found in the market of ACC systems for use in traffic, i.e. safe following systems on PTWs. ACCs become, on the other hand, more and more common in cars.

The ACC combines two features:

1. A comfort feature in automated speed control;

2. A safety and comfort feature in automated time headway control. Here the ACC is fed by information coming from one or more sensors.

The focus for PISa is safety and to support the PTW rider in automated time headway control: the comfort feature is nice to have, but not one of the primary aims for PISa. Therefore, it is not very wise to use the term ACC in the PISa project because it may induce a certain kind of misinterpretation. Instead, the abbreviation DSS (Distance Support System), a system controlling time headway and time to contact, fed by the IBEO sensor, will be used for the remainder of the PISa project. The first focus is to increase safety for longitudinal conditions: so, the DSS supports the rider intuitively, using haptic feedback, maintaining a

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safe time headway and time to collision. For the approach of this study, previous research on a haptic accelerator (gas pedal) is considered (Abbink, 2003 (doctoral thesis), Mulder, (2005 A, 2005 B) (doctoral thesis) and Pauwelussen, 2005 (Master Thesis)). This research focused on the development of a haptic feedback rider support system in which the man-machine interaction performance was examined by a control theoretical approach.

2.3 Distance Support System development for PTWs

This section provides background information about Distance Support System (DSS) development for PTWs. The aspects considered are:

• The baseline for the DSS;

• Driving phases;

• Haptic feedback;

2.3.1 The baseline for the Distance Support System

In the automotive industry a lot of systems are used to support the driver in keeping a safe distance in both longitudinal and lateral direction. These systems work with radar, laser and/or camera. A well known system is ACC, this system works with radar that tracks the distance and speed between the car in front and the car itself. The algorithm in the ACC controls the velocity of the own vehicle autonomously by taking into account the velocity set point from the driver and the distance between the vehicle and the car in front. One could consider the driver being out of the car following control loop, because the car following task is automated by the ACC.

For the DSS for the motorcycle an algorithm was developed that doesn’t control the speed autonomously, but provides an intuitive feedback force/torque to the rider when the distance is too close or the relative velocity is too high. In this case the rider will maintain in the car-following control loop and will be supported by the DSS. The DSS provides the PTW rider with haptic feedback when ‘danger’ is close by. This feedback system provides a torque to the handle bar ordering the rider to decrease the throttle, which can always be overruled by the rider. The DSS gets its information from the decision logic and controls the torque, with an aftermarket actuator and control algorithms developed for PISa. The DSS provides the rider with haptic feedback, over the right handlebar at the same time. The goal for the DSS is to develop an intuitive system for PTWs.

2.3.2 Driving phases

The aim for the DSS is to keep a save distance to the vehicle in front. This means that it must support the rider before getting into an unsafe situation. The PISa project wants to develop an entire system that includes the haptic throttle and, in a later stage, an autonomous braking system (AB) and a Brake Assist (BA). Both AB and BA can only be implemented successfully once we understand when and even more important when not to use these systems. Planned tests, within the PISa project, will test these systems for its use and safety. An overview of the system is graphically shown in Figure 2. The AB and a BA system both are active in the phase called the reaction phase, in which the rider is not controlling the distance anymore but must brake to get out of the dangerous situation.

The haptic throttle must work before the reaction phase, with the main purpose to keep the rider out of the reaction phase and in the regulation phase.

If the rider is in the regulation phase, also called the car following phase, and is going too fast or the vehicle in front is having a low velocity the rider must decelerate to stay out of the reaction phase.

DSS works in both stages; the regulation phase and the reaction phase. The regulation phase is the car following phase, in which the rider controls the desired separation with

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respect to the vehicle in front and the motorcycle. In this phase DSS provides haptic feedback which informs the rider when the distance is dangerously close.

The second stage of DSS is the reaction phase. In this phase the rider is not at the desired separation, but the situation is more dangerous. Here the rider has to respond quickly to return to the car following phase. The haptic throttle gives in this case maximum feedback to the rider informing him/her about the dangerous situation at hand. The logical reaction should be to close the throttle and to activate the brakes when needed. Another possibility to react to avoid the dangerous situation is longitudinal and lateral: here, the rider will avoid colliding with the obstacle while swerving around.

In the car following phase (see Figure 2) the rider is following a vehicle in front while controlling the time headway (THW) and time to collision (TTC). The THW is the time that it will take for the vehicle to drive the distance between the subject vehicle and the vehicle in front. This formula of THW is the relative position divided by the subject vehicle velocity:

11

12

v

s

v

ssTHW rel=

−= (2-1)

The THW provides information about the critical situation at one time by not looking at the near future (e.g. a car that starts to decelerate in the upcoming few seconds).

When the THW is small, the distance is small and/or the velocity of the vehicle is high, in that case the situation is more dangerous than with high THW.

The THW does not include information about the velocity of the vehicle in front.

The THW is a momentary value that provides a critical level (=distance in relation to the PTW speed) to anticipate on sudden changes in the behaviour of the vehicle in front. Therefore it is also important to consider the time to collision. The formula of the TTC is the distance between subject vehicle and vehicle in front, divided by the relative velocity.

rel

relrel

v

s

vv

sTTC =

−=

21

(2-2)

The biggest problem with TTC during investigating driving behaviour is the relative velocity. If the vehicles are driving the same velocity which is very common, the relative velocity is zero and therefore the TTC goes to infinity. This is why the TTC will be often inverted.

The reaction phase is the phase in which the rider has to react in critical situations. In that case the THW will be small and the inverted TTC is high. As shown in Figure 3.

Figure 3 The regulation phase and the reaction phase

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During car following the rider tries to follow the lead vehicle based on visual perception, from where the rider estimates the relative distances and velocities to judge the change of the throttle based on the desired THW or change of THW.

Figure 4 The schematic presentation of the system

To examine the car following performance, a car following model has been developed as shown in Figure 4. This is a Multi-Loop rider-motorcycle model based on the crossover theory (McRuer & Jex, 1967, Mcruer & Krendel, 1974).

2.3.3 Haptic feedback

Touching and feeling the environment is a rich, intuitive and essential channel for humans. Touch makes humans aware of an object and adds information to visual information such as roughness, heat transfer coefficient, stiffness and so on. Touch also makes people able to feel forces, resistances, and enables them to investigate properties of an object, which is not possible by the visual information channel only. During car following, the visual channel is already highly loaded and a flashing light (visual feedback) might overload the rider. Touch is another part of the brain which is not highly loaded during driving a vehicle or riding a motorcycle with regard to car following, which means it can be stimulated without distracting the sight. That is how the idea came to light using haptic throttle feedback. It is assumed that the right hand is the best place for the haptic information, because this hand is already controlling the longitudinal dynamics of the motorcycle (both accelerating and decelerating).

There are already other haptic sources that riders feel during riding their motorcycles such as wind noise, engine noise/vibrations, and accelerations to use for controlling the motorcycle; but this information is mainly related to the state of the motorcycle and not about their environment (vehicles driving around the motorcycle). When for instance the visual perception is limited by heavy rain, fog or limited light it is more difficult for the rider to estimate relative velocities and distances and there are possibilities that the rider is not aware that he is driving into the reaction phase. Haptic feedback on the throttle was chosen to inform the rider, because this provides continuous information about following distance. The magnitude of the torque is dependent on the algorithm which uses the input variables such as motorcycle velocity, relative distance and relative velocity. It is also believed that riders are better in controlling a force task than a visual task (Mulder, 2004). The schematic presentation of the model is shown in Figure 5.

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Figure 5 The schematic presentation of the haptic feedback control system

A wide range of warning devices can be used for the PISa safety systems: visual, audio, tactile, haptic etc. The visual channel is loaded as the rider has to look out when riding a PTW. The audio channel is difficult to use in the loud environment easily masking any kind of audio warning. The tactile channel seems to be a feasible solution, given a simple warning needed for the PISa safety system. A tactile display is an array of small vibrating elements, called tactors, which are in indirect contact with the skin. For example, when a mobile phone vibrates, it is a tactile display that lets the user feel that an incoming call is waiting to be answered. As long as the tactors have a reasonable contact with the skin and are vibrating strongly enough, the tactors can be felt under high vibration or bumpy conditions. The tactile warning device is discussed in more detail in section 3.3.

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3 Human Machine Interfaces specifications for PTWs

3.1 Distance Support System and haptic throttle HMI

The activities, for the DSS, consisted of:

1. The development of a haptic feedback algorithm based on experimental data from a pilot experiment;

2. The development of a non-linear longitudinal dynamic control algorithm involving control/response data from the experimental data described above;

3. The development of hardware to control the feedback torque and the engine power-setting.

3.1.1 The haptic feedback algorithm

The rider uses the throttle to control the PTW longitudinally. One of the tasks is to keep a proper and safe distance between the PTW and the vehicle followed by the PTW. The aim of the DSS is to help the rider in maintaining a safe distance, or time headway for the regulation phase. The idea is to provide force feedback to the rider when dangerous situations are imminent. The force feedback is given to the rider using the throttle using a special force feedback algorithm. The challenge is that the amount of force feedback is not known. As such, we developed and tested various force feedback algorithms for use in the DSS. The force feedback may not be too low with a chance of being unnoticed. At the same time, it may not be too high causing PTW rider fatigue.

The DSS algorithm calculates the needed deceleration in order to stay out of the reaction phase, for example:

When a motorcycle is riding with a velocity of 144 km/h or 40 m/s. and a vehicle in front is driving 108 km/h or 30 m/s constantly the motorcycle needs to decelerate to stay out of a collision, at 80 meters headway the TTC is 8 seconds and the THW is 2 seconds. If the motorcycle now decelerates with 1 m/s², after 10 seconds the distance is decreased until 30 m and the relative velocities of the motorcycle and vehicle is 0, in this case the THW is decreased at minimum value of 1 second. This example is graphically shown in Figure 6.

Figure 6 Situational sketch

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As in the example the desired deceleration (in the example 1 m/s²) needs to be estimated for every situation, to stay out of the reaction phase that is assumed in the first instance at a THW of 1 second or less.

3.1.2 Pilot experiment 1: Level of haptic force feedback

A pilot experiment was carried out, using various PTW riders, in order to determine the way (the shape) and the amount of haptic force feedback needed for the DSS. A tabletop motorcycle driving simulator was constructed to investigate throttle/human interaction; there was no brake pedal and handle or a way to shift gear. The simulated throttle (right handle of Figure 7) could deliver torque levels independent from the position and therefore made it ideal to test torques during car following. The torque actuator was software controlled and can be used to deliver the haptic feedback required for the experiment. The throttle was electromechanically powered. A colour LCD display was mounted right behind the throttle indicating the velocity and engine revolution indicators during the experiment. A 30 inch LCD display with a resolution of 2560 x 1920 pixels was used to give the visual information to the rider: the rider could see the road, car in front etcetera.

Figure 7 Simulated gas handle

Method

The subjects were instructed to follow a car in front using the throttle, the car in front kept a constant velocity of 80 [km/h]. The motorcycle (controlled by the subjects) started from a standstill and had to accelerate to catch up with the car in front: the test person controlled the headway. If the THW got below 4 seconds an additional torque was given increasing in force with decreasing THW. The build up of the torque and the THW was either linear or exponential. Two different maximum torques and two different build up curves, resulting in four conditions (see Figure 8 and in Table 2), (linear or exponential) were investigated. The four conditions were balanced amongst the subjects to avoid any kind of order effects. The subjects were asked to rate each of the four conditions using a questionnaire. The subjects were also asked about the moment they sensed feedback. The test person completed the questionnaire after every condition. The subjects judged/rated:

• the effort it took to follow the car;

• the development and magnitude of the torque;

• moment of torque build-up.

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Figure 8 Characteristics tested during the experiment to determine the maximum torque

Table 2 Different torque levels

Torque development Shape Maximum torque [Nm]

1 Linear 1

2 Exponential 1

3 Linear 0.75

4 Exponential 0.75

Subjects

The test was completed by 11 subjects including experienced and inexperienced PTW riders.

Results

Level:

The subjects were asked for their preference, after each condition, for the torque level and preferred shape (linear or exponential). The majority (90%) of the subjects disliked the highest feedback level of 1 Nm. They commented upon the fact that riding became too exhausting with this amount of feedback. The lower level (0.75 Nm) was much less exhausting and was preferred: the resulting force was not too high but high enough to be sensed.

Build up:

There was a clear preference for the linear torque build up: the 85% of the subjects could feel the DSS being activated clearly. Hence, they felt this was a clear and intuitive signal. The exponential torque build up, building up slowly, did not give such a clear signal: the activation of the DSS could not be felt clearly.

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3.1.3 The Distance Support System algorithm

An algorithm to use as control logic for the DSS was developed using the results from the pilot experiment described above. Two parameters were used for the algorithm: time headway (THW) and time to contact (TTC). THW only is not sufficient for a DSS: the TTC will be too small when the speed of the PTW is much higher than the car that is being approached because of a limited deceleration power of the PTW’s engine only.

This section will describe the algorithm used to control the DSS. It starts with a theoretical background in acceleration, time headway (THW) and time to contact (TTC). The next step is to describe the actual control algorithm. The last step is to describe when the algorithm works and where it does not work, that needs to be solved by additional systems. The algorithm also includes a map that contains the maximum deceleration without using the brakes of the motorcycle to achieve a better system that is suited for this PTWs in general.

The relationship between THW and TTC

Figure 9 shows the relationship between acceleration, and TTC for various relative speeds (vrel = the speed between the PTW and the vehicle in front of the PTW). The required deceleration is based on the start of the reaction phase at a THW of 1 second; v1 represents the motorcycle velocity (in km/h) and vrel represents the relative velocity (in km/h) between motorcycle and vehicle in front.

Figure 9 TTC over the desired acceleration for different conditions

It is clear that all the curves are velocity and relative velocity dependent, which means that there is no curve that can be used for all situations. For the algorithm a more complex algorithm is needed than just giving feedback when the THW or TTC drop below a certain value.

The distance between two vehicles is calculated using the following formula:

2

0 21 tatvss relrelt ⋅⋅−⋅−= (3-1)

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Where:

=t Time [s]

=ts Distance at time t [m]

=0

s Distance at time 0 [m]

=1

v Velocity of vehicle [m/s]

=2

v Velocity of lead vehicle [m/s]

=relv Relative speed ( )21

vv − [m/s]

=rela Relative acceleration (in this case the required acceleration) [m/s²]

=min

THW The minimum Time Headway [s]

ts is used for the minimum distance between two vehicles at the minimum THW.

2minvTHWst ⋅= (3-2)

The time from t=0 till the minimum THW can be calculated by:

minTHW

a

vt

rel

rel −−= (3-3)

If Formula 3-2 and 3-3 are substituted in 3-1 and solved to rela it will give:

2

min

22

min

2

min

2

2min20

2

0min202

THW

vTHWTHWvTHWvssTHWvsa

rel

rel

⋅+⋅+⋅⋅⋅−±⋅−= (3-4)

The complete algorithm is shown in Appendix A.

This algorithm provides a cue for the needed deceleration value in the regulation. The algorithm ensured that the PTW stays out of the reaction phase given a certain relative

velocity between the PTW and the lead vehicle. For the deceleration algorithm, min

THW is

taken at 1 second because here is assumed that the rider enters the reaction phase when

minTHW becomes equal or smaller than 1 second.

The curves that match the formula are shown in (Figure 10). This is done by subtracting the velocity from the distance and dividing it by the relative velocity. Hence, these curves are independent from velocity.

These curves are used by filling in both the relative velocity (vrel) and

relv

THWvsmin1

⋅− to

determine the needed deceleration.

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Figure 10 (s-v1xTHWmin)/vrel over desired acceleration

This formula is very useful because this can be used as a danger level, because with lower

relv

THWvs min1⋅− the higher the deceleration needs to be to reach a THW of 1 sec.

The shapes of the curves are exponential. With high

relv

THWvs min1⋅− there is a very small

slope of deceleration (that is coupled to feedback). However, the results from the pilot experiment showed that the subjects preferred a clear and distinctive start of the DSS. In order to overcome the shortfall of the formula, an additional algorithm was developed. This is described in the next section.

DSS control algorithm with additional feedback

The algorithm shown in Section 3.1.3 works only in the regulation phase, with a larger THW,

because the algorithm calculates the deceleration needed to achieve a THW of 1 sec., which

is assumed to be the beginning of the reaction phase. If for some reason the PTW gets into

the reaction phase there has to be maximum feedback to the rider, for this a simple THW

control is used that builds force feedback up with decreasing THW smaller than 1 sec. This

additional feedback is stored in a lookup table (from THW 1 until 0.8 sec). The feedback

builds up to a maximum of 0.75 Nm and stays at its maximum until a THW of 0 sec. This

build up has been determined by some experienced motorcycle riders riding the simulator.

This lookup table can be seen in the overall Simulink model in Appendix B.

(s-v1xTHWmin)/vrel over Acceleration for different vrel

0

2

4

6

8

10

12

-3 -2,5 -2 -1,5 -1 -0,5 0desired acceleration [m.s^-2]

(s-v

1xT

HW

min

)/v

rel [s

]

vrel=15 [m/s]

vrel=10 [m/s]

vrel=7.5 [m/s]

vrel=5 [m/s]

vrel=2.5 [m/s]

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The small deceleration slope, at the beginning of feedback, was not preferred by the subjects

(see section 3.1.2). This is solved by giving a step in the feedback by a switch if the

relv

THWvs min1⋅− (see Figure 11) drops below a value of 10.

Figure 11 Step of haptic torque for start of feedback

Deceleration translated to Feedback.

The achievable deceleration, using the throttle only, is velocity dependent, because the

driving resistance is mostly air resistance. Therefore, we included this as an extra algorithm

in the lookup table used. This algorithm is effective for a too low THW providing a

deceleration, to be translated to a feedback torque on the throttle.

This is achieved by storing the maximum deceleration possible (from the non-linear

longitudinal dynamics model) at a certain velocity in a lookup table. And this has to be

compared by the deceleration of the output from the lookup tables.

The feedback torque is calculated by:

max

max

Ma

aM desired

Feedback ⋅= (3-5)

Where:

maxa

adesired is saturated between 0-1 [-] (3-6)

How this all is realised in a Simulink model can be seen in Appendix B.

3.2 The Distance Support System hardware

For the development of the DSS an actuator is needed, able to generate the haptic torque on the throttle and to control the engine setting at the same time (the throttle handlebar, the engine fuel controller and the actuator are 1 to 1 attached to each other). The type of actuator must be installed in the PISa test bike and must provide a good balance between performance, size and costs.

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3.2.1 Hardware for the actuator

The actuator that is chosen is a pneumatic actuator. This actuator is part of an aftermarket cruise control system for motorcycles (see Figure 12).

Figure 12 Example of a pneumatic actuator on motorcycle

This actuator is connected, using a Bowden cable, to the electronic fuel injection system of the PTWs engine and the throttle handlebar. The actuator can generate a pulling force, over the Bowden cable which is on one side attached to a membrane that can be moved by varying pressure on the other side of the membrane. The characteristic of the actuator is shown in Figure 13.

Figure 13 Actuator characteristic

This characteristic shows that the actuator force is proportional with the pressure. The formula of pressure is:

ApF ⋅=

Where:

p= Pressure

A= Effective membrane area

F= Force on the cable

The maximum force on the Bowden cable is 51 [N] at a pressure of 170 [mbar] (almost vacuum). This corresponds to a maximum throttle handlebar torque of 1 [Nm] (assuming that

0

10

20

30

40

50

60

0 20 40 60 80 100 120 140 160 180

Under pressure (mbar)

Ca

ble

Fo

rce

(N

)

20

the arm of the throttle handlebar is 20 [mm]). Thus, the actuator delivers a sufficient maximum force for the DSS. The vacuum needed for the actuator is supplied by the vacuum pressure created in the combustion inlet channel of the engine (see Figure 14), also known as the manifold air pressure (MAP).

Figure 14 Situational sketch of the engine vacuum

The actuator has to be connected to the combustion inlet channel of the engine using a small hose for its needed vacuum. This ‘vacuum hose’ connects to the actuator with two valves, to control the pressure inside the actuator and thereby the actuating force, are installed inside the actuator. One valve is used to supply another to dump vacuum. These valves are controlled by a relay, which is electronically connected to the decision logic control box developed for PISa by UNIFI. The relay interfaces with the decision logic using a CAN-bus interface. A bang-bang control with hysteresis design was chosen to operate the two valves.

A bang-bang control is a simple control algorithm which supplies vacuum in the actuator when the amount of vacuum is too low or dumps vacuum if it is too high. The pressure sensors used can measure pressure differences of 1 [mbar]. With this control algorithm the valves open and close on the adjusted control frequency always even if the set point is constant and the engine vacuum is constant, because of noise during measurement. The result is a good performance with fast response on changes but not a totally constant force because of the high rate of switching from the valves, every switch operation from the valves can be felt as a jerk in the throttle handle. Hysteresis adds a margin to the previously discussed bang-bang control where the pressure in the actuator can change till the vacuum in the actuator is adjusted by the valves. With this design the performance of the controlled system is better than without hysteresis, because the rate of switching from the valves is reduced which adds a significantly lower fluctuation frequency on the cable. In this design there is also more room for tuning of the desired response because the amount of hysteresis can be set as a constant or dependent on the set point.

21

3.2.2 Actuator control algorithm

The control algorithm for the actuator is programmed in Simulink Stateflow (see Figure 15). The inputs used for this algorithm are the actuator pressure, the pressure margin and the outputs are the states of the valves (open or closed). The Stateflow block is included in the overall Simulink model which can be found in Appendix C.

Figure 15 Stateflow diagram

Possibilities of tuning

In the concept stage of the control design the system was tested, in a tabletop setting, with help of a vacuum pump delivering the needed vacuum. To get a better control strategy in real-world conditions, e.g. on the motorcycle, a map sensor could be needed into the system in order to compensate for differences in MAP pressure (or vacuum): the engine will generate a ‘high vacuum’ at idle speed and a ‘lower vacuum’ at wide open throttle (WOT).

Parameters of the actuator control algorithm, which can be modified/tuned in the software are:

• The crossover frequency from the Low-Pass filter from the actuator sensor can be changed to reduce sensitivity on high frequency fluctuations.

• The extent of hysteresis can be changed to reduce the switching of the valves.

Different parameters can be changed in the hardware:

• Changes to involve the safety dump valve into the control, with the safety valve the vacuum can be dumped quicker.

• The change from the extent of hysteresis has the most effect on the response of the actuator

22

3.2.3 Physical design and interfacing

The DSS hardware (Vacuum actuator, valves and pressure sensors) should all be mounted close to the throttle on the engine. There is just one CAN hardware interface for both the actuator valves and the pressure sensors. All electronic components should be mounted in a waterproof box as they are not yet protected from the elements (see Appendix D). Power supply is onboard 12V system. The CAN interface specification is explained in Appendix E.

3.3 The tactile saddle Human Machine Interface

This section specifies how to embed the tactors from TNO in the saddle of the PISa test bike: the Malagutti Spidermax. It will be used to display signals from the decision logic unit. The display will present two signals to the PTW rider: the first signals a pre-warning, warning the PTW rider that the DSS will be activated within 0,25-0,35 seconds in order to prevent the occurrence of a possible hazardous situation, with a signal initiated by the IBEO laser sensor, which requires the riders attention. The second signal warns the PTW rider that he/she has to use his/her brakes in order to avoid a collision since the system is not able to decelerate the PTW enough. Clearly the second signal is much more intrusive than the first.

The sections below go into detail about: the physical design (section 3.3.1) of the tactors in the Malagutti Spidermax Saddle and the electrical design (section 3.3.2) for the tactile saddle. Section 3.3.3 is about the signal design.

3.3.1 Physical design

The type of tactors that TNO usually uses in tactile displays is JHJ-3. A JHJ-3 tactor is a small plastic box that contains a small electric motor connected to an eccentric weight. The size of the box is 22 x 16 x 10 mm (l*w*h). It is important that most of the vibrational energy is transferred to the skin. However, the saddle cover and the motorcyclist’s trousers will hamper the propagation of vibrations to the skin. In order to get a good transfer and still have a comfortable saddle, it is proposed to partially embed the tactors in the foam of the saddle (see Figure 16). Recently, tactors have been embedded in a desk chair in the same way and after one hour the users did not feel discomfort. To make sure that enough tactors are in contact with the skin, it is proposed to place the tactors under the upper legs (see Figure 17) and activate them all simultaneously.

23

Figure 16 A JHJ-3 tactor partially embedded in foam. An accelerometer (in black and copper) has been attached to the tactor (white block).

Figure 17 Configuration of tactors in the saddle of the Malagutti Spidermax. The tactors are located under the left and right leg

3.3.2 Electrical design

The JHJ-3 tactor has a thin wire attached to it that has to be connected to The control hardware should be capable of providing 1Altogether the control hardware should be able to source 960 mA. In addition, it should be capable of switching the tactors on and off with a time rebox has to be designed such that it can control the tactors. Close coUNIFI and TNO is elementary for this activity. Eventually, an extra control box, linking the PISa decision control box with all tahardware and software. Since all tactors are activated together and a very limited number of tactile signals will be used, the hardware and software can be very simple.

3.3.3 Signal design

One or two signals will be used, pending the outcome of a small experimentof the planned track tests within the PISa projectintrusive, signal, described below is and the second signals will be used. Two signals are defined: the first signal warns the that there is a possibly hazardous situation going on, that requires the second signal should tell the proposed to activate all tactors simultaneously in both situations to be sure that the

Configuration of tactors in the saddle of the Malagutti Spidermax. The tactors are located under the left and right leg (the arrow shows the driving direction)

3 tactor has a thin wire attached to it that has to be connected to The control hardware should be capable of providing 1-3 Volts (DC) and 60 mA per tactor. Altogether the control hardware should be able to source 960 mA. In addition, it should be capable of switching the tactors on and off with a time resolution of 10 ms. The PISa control box has to be designed such that it can control the tactors. Close co-ordination between UNIFI and TNO is elementary for this activity. Eventually, an extra control box, linking the PISa decision control box with all tactors, may be opted for. The second requires customhardware and software. Since all tactors are activated together and a very limited number of tactile signals will be used, the hardware and software can be very simple.

will be used, pending the outcome of a small experimentof the planned track tests within the PISa project. When using one signal the secondintrusive, signal, described below is only used. Obviously, when using two signals, the

be used. Two signals are defined: the first signal warns the that there is a possibly hazardous situation going on, that requires the rider’ssecond signal should tell the rider to take immediate action to avoid

to activate all tactors simultaneously in both situations to be sure that the

24

Configuration of tactors in the saddle of the Malagutti Spidermax. The e driving direction).

3 tactor has a thin wire attached to it that has to be connected to control hardware. ) and 60 mA per tactor.

Altogether the control hardware should be able to source 960 mA. In addition, it should be solution of 10 ms. The PISa control

ordination between UNIFI and TNO is elementary for this activity. Eventually, an extra control box, linking the

ctors, may be opted for. The second requires custom-built hardware and software. Since all tactors are activated together and a very limited number of tactile signals will be used, the hardware and software can be very simple.

will be used, pending the outcome of a small experiment at the beginning . When using one signal the second, more

used. Obviously, when using two signals, the first be used. Two signals are defined: the first signal warns the rider

rider’s attention. The on to avoid the collision. It is

to activate all tactors simultaneously in both situations to be sure that the rider can

25

feel the signal. The first signal should have the feel of a notification. Therefore, a triple tactile pulse of 200 ms each, with 100 ms in-between the two pulses is proposed. The signal is not repeated.

For the second, intrusive, signal, we propose a continuous activation of the tactors until the rider takes appropriate action (e.g. braking) or the danger has past is proposed. The continuous activation of the tactors gives a very strong sensation. As an alternative signal a repeating signal, in which the tactors are on for 1000 ms and off for 200 ms could be used.

26

4 Conclusions and recommendation

This report discussed the theoretical background behind PTW BA, AB, ACC, DSS and related warning devices from an HMI point of view. Furthermore, the control algorithms for the DSS and its hard and software were specified in detail. Similarly, a specification was given for the tactile saddle, both in signal, electrical and hardware. This tactile saddle will be used as the warning device for the PISa project.

It is recommended, before any formal testing of the PISa test bike, to fine-tune the actuator control algorithm of the DSS. This system was tested for its functionality using a tabletop setting. Further fine-tuning is needed in order to provide the first test riders with a proper haptic feedback.

27

5 Sources

5.1 Reference List

Abbink, D.A., (2003) Admittance measurements during maximal position tasks and relax tasks (Progress memo). Delft University of Technology - Faculty of Mechanical Engineering - Human Machine Systems Group, the Netherlands

Mulder, M., Mulder, M., van Paassen, M.M., Abbink, D.A. (2005A) Identification of Driver Car-Following behaviour, IEEE-SMC 2005

Mulder, M., Mulder, M., van Paassen, M.M., Abbink, D.A. (2005B) Effects of Following Vehicle Speed and Separation Distance on Driver Behavior

Maids project (2004), The first complete European in-depth study of motorcycle accidents, European project

Pauwelussen, J.J.A. (2005), Design of an Intelligent Driver Support System including Deceleration Control, Master of Science Thesis, Aerospace Engineering, Delft University of Technology

D03, Summary of knowledge, issues and techniques relevant, 2006, PISa EU Project, CONTRACT N. TST5-CT-2006-031360

D12, User Information, 2007,PISa EU Project, CONTRACT N. TST5-CT-2006-031360

D15, Detailed Case Summaries and detailed video footage, 2007, PISa EU Project, CONTRACT N. TST5-CT-2006-031360

D17, A set of dynamic states and parameters, 2007, PISa EU Project, CONTRACT N. TST5-CT-2006-031360

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6 Appendices

6.1 Appendix A

=ts Distance at time (t)

=0

s Distance at time (0)

=1

v Velocity of vehicle

=2

v Velocity of lead vehicle

=relv Relative speed ( )21

vv −

=rela Relative acceleration (in this case the required acceleration)

=min

THW The closest Time Headway

2

min

22

min

2

min

2

2min20

2

0min20

min

2

2

min

0

2

min

2

2

min

2min

2

0

2min

2

0

2

min

2min

22

min

0

min

2

02min

2

02min

2min

2

0

2

22

22

22

22

21

21

21

THW

vTHWTHWvTHWvssTHWvsa

THW

v

THW

s

THWa

va

THW

vTHWa

vs

a

vTHWa

vsTHWa

vTHWa

vTHWas

THWa

vt

tatvsvTHW

tatvsvTHW

vTHWs

tatvss

rel

rel

rel

relrel

rel

rel

rel

rel

relrel

rel

relrel

rel

rel

relrel

relrel

t

relrelt

⋅+⋅+⋅⋅⋅−±⋅−=

⋅−

⋅+

⋅=

⋅−+⋅

=

⋅⋅−+⋅=⋅

⋅+⋅

−⋅

=

→

−−=

⋅⋅−⋅−=⋅

⋅⋅−⋅−=⋅

→

⋅=

⋅⋅−⋅−=

⋅

The negative version of the formula matches the desired deceleration.

For the deceleration algorithm, min

THW is taken at 1 second because for smaller values than 1

second it is assumed that the rider is entering the reaction phase.

29

6.2 Appendix B

Figure B-1: Simulink haptic feedback model

Figure B-2: Longitudinal motorcycle dynamics model

30

6.3 Appendix C

31

6.4 Appendix D

32

33

34

6.5 Appendix E

CAN Message specification DSS

CAN messages: 500Kb, standard identifiers

Message 0x110 from Actuator to DL, 8 nbytes, 500Hz, Big Endian

CAN bit

Byte0 hi-nibble bit 4~7 bit 12~15 AD0 P_actuator [0..1023] mbar

lo-nibble bit 0~3 bit 8~11 bit 8~11

Byte1 hi-nibble bit 4~7 bit 4~7 bit 4~7

lo-nibble bit 0~3 bit 0~3 bit 0~3

Byte2 hi-nibble bit 4~7 bit 4~7 AD1 P_engine [0..1023] mbar

lo-nibble bit 0~3 bit 0~3 bit 8~11

Byte3 hi-nibble bit 4~7 bit 4~7 bit 4~7

lo-nibble bit 0~3 bit 0~3 bit 0~3

Byte4 hi-nibble bit 4~7 bit 4~7 not used

lo-nibble bit 0~3 bit 0~3 not used not used

Byte5 hi-nibble bit 4~7 bit 4~7 not used

lo-nibble bit 0~3 bit 0~3 not used not used

Byte6 hi-nibble bit 4~7 bit 4~7 not used

lo-nibble bit 0~3 bit 0~3 not used not used

Byte7 hi-nibble bit 4~7 bit 4~7 not used

lo-nibble bit 0~3 bit 0~3 not used not used

Message 0x200 from DL to Actuator, 2 bytes, 500Hz

Byte0 hi-nibble bit 4~7 bit 4~7 supply valve

lo-nibble bit 0~3 bit 0~3 bit 0 [0/1]

Byte1 hi-nibble bit 4~7 bit 4~7 dump valve

lo-nibble bit 0~3 bit 0~3 bit 0 [0/1]