Autonomous mobility scooter requirements

To go back to the mainpage: PRE2017 3 Groep6.

in order to make a product or a model of the system, it must first be decided what the actual requirements and limitations of our model are. with these requirements we can see what our model should eventually do.

we have split the requirements in four different sections, to split main concerns of the system.

navigation: these requirements concern everything to with the software and navigation, what it should, can, cannot or should not do.
safety: these requirements concern safety issues of a mobility scooter.
smart mobility: these requirements concern how to enhance the mobility scooter such that it responds to the requests of the user.
physical: these requirements concern the actual hardware that is needed for the mobility scooter.

1. the mobility scooter can navigate through a shop.
2. the mobility scooter can navigate through a door(850mm).
3. the mobility scooter can use elevators(1050mmx1500mm).
4. the mobility scooter can use public transport( be able to acess the wheelchair ramps).
5. when the mobility scooter encounters an obstruction, the mobility scooter will alter it's path to go around the obstruction.
6. the mobility scooter will offer up to three alternative paths to the destination.
7. the mobility scooter can navigate regardless of the lightlevel
8. the mobility scooter can navigate when it is raining
9. the mobility scooter can navigate through fog, when visibility is less than 50 meters
10. the mobility scooter can drive through snow less than 5 cm deep.
11. the mobility scooter can differentiate between a road and a cycle path.
12. when the mobility scooter encounters a trafficlight, the mobility scooter can determine which light of the trafficlight is on

safety

1. The mobility scooter can not drive faster then 6 km/h on a walking path.
2. the mobility scooter should not get closer than 10 centimetres to another person while driving.
3. if the autonomous system detects a failure, it notifies the user through the use of sound.
4. The mobility scooter can detect change in height in the road ahead. (curbs, speedbumps, holes, ramps)
5. The mobility scooter can detect a berm.
6. The mobility scooter can detect Bushes.
7. The mobility scooter can detect Cyclists.
8. The mobility scooter can detect pedestrians.
9. The mobility scooter can detect animals.
10. The mobility scooter can detect motorised vehicles.
11. The mobility scooter will not fall over.
12. The driver of the mobility scooter can not fall out of the scooter.
13. The mobility scooter should allow the driver to intervene, if they don't trust the scooter.
14. The mobility scooter should not cause bodily harm when a failure occurs.
15. The mobility scooter should notify the user through the use of sound and visual display when the sensors are blocked. (Also UI related)
16. The mobility scooter can safely move to a safe spot when the battery is less than 10% full.
17. <- what is safe?
18. The mobility scooter can safely operate with a driver of up to 125kg.
19. The mobility scooter will stop moving if the driver falls out.
20. The mobility scooter will give auditory and visual feedback if a wheel has been blocked.
21. The mobility scooter can override the driver input when collision is imminent. (Not unusual that the applies the accelerator when trying to brake. Another example is that the driver wants to go forward but the scooter is in reverse)
22. Will not tilt and fall when driving on a surface with a slope of more than 10° "(ratio 1:5)".
23. The mobility scooter can not drive if there is no driver on the mobility scooter

smart mobility

1. The mobility scooter has a display with a diameter of 15 to 25 centimeters, which is visible on a bright sunny day.
2. The mobility scooter has a speaker system which provides auditory feedback in case of unexpected actions.
3. The scooter allows the user to set their destination using the display and change the brightness.
4. The scooter allows the user to set their destination using voice commands.
5. The scooter allows the user to change the volume level for the speakers, and pre-set destinations of choosing.
6. The scooter allows a user to get in using up to 60 seconds. No guidelines found yet, 60 seconds seems long but these users will not get off a lot.
7. The scooter provides visual feedback to the user, by means of flashing lights on the dashboard in case of emergencies and imminent danger.
8. The scooter can 'warn' people in vicinity of the scooter, by using its speakers.
9. The scooter can be controlled through the use of either a steering wheel, a joystick or voice commands.
10. The scooter can connect to the user's smartphone and make use of the included functions (calling, messaging).
11. The scooter maintains a connection to the internet. A smartphone connection renders this redundant, but it should be available
12. The scooter can self-initiate a call in case of an emergency.
13. The scooter can communicate with other scooters to gather and share sensory information in their environment.

physical

1. the mobility scooter should have batteries that can last 3 hours of driving time
2. the mobility scooter should have a computer system built in such that it can process the massive amount of data
3. the mobility scooter should have wireless communication to other vehicles
4. the mobility scooter should have wireless communication with a server
5. The autonomous mobility scooter will have flashing lights.
6. The autonomous mobility scooter will have whit front lights.
7. The autonomous mobility scooter will have red back light.
8. The mobility scooter through a standard door (dimensions to be added)

legal requirements

1. The mobility scooter will not drive faster than 6km/h on a side walk
2. The mobility scooter will not drive faster than the speed limit when on a bicycle path
3. The mobility scooter will not drive faster than 30 km/h on a bicycle path inside the built up area.
4. The mobility scooter will not drive faster than 40 km/h on a bicycle path outside the built up area.
5. The mobility scooter will not drive faster than 45 km/h on a regular road.
6. The mobility scooter will not drive faster than the speed limit when on a regular road.
7. When driving on a bicycle path the autonomous mobility scooter will not drive next to an other mobility scooter.
8. When driving on a regular road the autonomous mobility scooter will not drive next to an other mobility scooter.
9. When driving on a sideway the mobility scooter will obey the right of way rules for pedestrians.
10. When driving on a bicycle path the mobility scooter will follow the right of way rules for mopeds.
11. When driging on a regular road the mobility scooter will follow the right of way rules for mopeds.
12. The mobility scooter will use flashing lights when changing driving directions.
13. The mobility scooter will have his light on between 30 minutes before sunset and 30 minutes after sunrise when it is being used.
14. The mobility scooter will ahve its light on during bad weather when it is used.

reasoning

1. As many of the incidents are caused inside shops, and people get stuck in shops sometimes, we believe this is a necessary requirement to add [1]
2. As a mobility scooter cant use escalators or stairs, there will often be a situation where it would have to take the lift
3. A user of a mobility scooter often cant travel far because they rely on their mobility scooter. If they are able to use public transport, they arent limited by the range of their mobility scooter
4. this is trivial for autonomous driving systems[1]
5. a user may want to take alternative routes to a destination to take a more scenic route. [1]
6. the mobility scooter should still be able to navigate itself when in a dark room, or outside when its dark. this would mean that the mobility scooter cant simply rely on normal cameras.
7. if its raining, the sensors should not be able to be obstructed by the rain this is necessary for the choice of sensors and where to place them
8. if it is foggy, the sensors should not be able to be obstructed by the fog this is necessary for the choice of sensors
9. if there is only a small amount of snow, a mobility scooter user should still be able to go outdoors and do their usual stuff. especially since mobility scooter users are less mobile, a small amount of snow would block them from going outside as it can be slippery, but with the mobility scooter they could still go out and get food etc.
10. the mobility scooter should differentiate between a road and a cycle path such that it knows where it has to drive, and what kind of obstacles there are.
11. as the mobility scooter can encounter quite a few traffic lights when driving towards the destination, it is necessary that the autonomous vehicle can read and understand traffic lights.

[1] = user scenario

safety

1. the mobility should not cause danger for the user or the other road users
2. the mobility scooter should keep a safe distance from other people to avoid collision
3. if there is an error in the system, it should notify the user somehow, we believe he best way of doing this is through using sounds. this does however need more research.
4. the mobility scooter should have the ability to see bumps and holes in the road to make sure it goes over them safely.
5. part of the autonomous system to see the side of the road
6. part of the autonomous system to see the side of the road
7. part of the autonomous system to detect obstacles
8. part of the autonomous system to detect obstacles
9. part of the autonomous system to detect obstacles
10. part of the autonomous system to detect obstacles
11. we consider this to be trivial, falling over should not happen in any case
12. the mobility scooter shouldnt be able to cause the user any harm, and prevent it when possible
13. in case of the scooter making a mistake without detecting it, the user should always be able to take over
14. the mobility scooter shouldnt be able to cause the user any harm, and prevent it when possible
15. if sensors are blocked, it should notify the user such that the user can make sure nothing goes wrong
16. if the battery would suddenly die, the user would get stranded
17. if the driver is too heavy, braking is alot more difficult, and would have a high chance of crashing into an obstacle
18. stopping the vehicle would prevent any more injuries as the vehicle could just drive on since its autonomous
19. to notify the user that there is something wrong with the scooter and the user can act correspondingly
20. similar to what cars have these days, if a collision is imminent, the vehicle would brake in any case to minimise any possible injuries
21. the mobility scooter shouldnt be able to cause the user any harm, and prevent it when possible.
22. similarly to a driver falling off the mobility scooter, to prevent any injuries caused by a self driving vehicle not having a driver to make sure everything goes alright

Smart Mobility

1. 15-25 cm diameter ensures proper visibility while not hogging weight and space on the scooter
2. obvious, for safety reasons.
3. changing brightness provides less strain on the eyes at night while ensuring visibility in daytime.
4. in case the user's hands are disabled or occupied, voice control is a useful asset.
5. the volume needs to be low or muted in libraries, for example. In busy streets it needs to be louder. Pre-set destinations save time and offer better customer service for users having trouble remembering addresses.
6. 60 seconds is not a lot considering most users will be in their mobility scooters for longer periods of time, but enough to ensure people can get on in time.
7. Like cars do already, flashing red lights on the dashboard are proper notifiers to pay extra attention to the road.
8. does not need further explanation.
9. Various control methods for various users with various different handicaps.
10. Connecting a smartphone enables various options without having to implement these in the scooter (like calling and messaging systems)
11. In case a user does not own a smartphone, it needs to connect to the internet on itself, in order to navigate properly and share information with other scooters.
12. In case the user is not able to make a call anymore (e.g. having a stroke).
13. This in order to make traveling by scooter as efficient as possible, and also enable other autonomous verhicles to profit from the sensory data.

Physical

1. if the range would be very low, it would limit the freedom of the user quite alot, which is what we are trying to avoid
2. trivial necessity of an autonomous system
3. with wireless communication to other vehicles, we could improve the safety, by sharing navigation details (this needs further research)
4. communication with a server might help reducing the computational load on the mobility scooter (needs more research)
5. We want the mobility scooter to be able to drive on public roads. Using flasing light is required by law when drining on public road. So the mobility scooter needs to have flasing lights
6. We want the mobility scooter to be able to drive on public roads. Having white front lights is required by law when drining on public road. So the mobility scooter needs to have white front lights
7. We want the mobility scooter to be able to drive on public roads. Having red back lights is required by law when drining on public road. So the mobility scooter needs to have red back lights
8. In the user story the mobility scooter is used by a user to get form insite his home to inside de supermarket. To get out his home the scooter need to fit through a standard door.

Legal requirements

All of these requirement follow from the law.

Solutions

recognising the difference between road, cycle path and footpath
As an important part of our mobility scooter, the mobility scooter will need to know the difference between a road, a cycle path and other types of road.
Each of these different types of road have different users and laws which the mobility scooter has to account for accordingly. In addition to other road users, there are also a number of different types of road markings. Currently there are numerous different types of roads: roads with or without cycle path and with or without a footpath.
In order to know which path the mobility scooter is driving on, we first have to define what a footpath and cycle path is.

footpath
According to https://nl.wikipedia.org/wiki/Trottoir a footpath is a heightened piece of road often paved or bricked.

in this case, the software system would have to recognise this heightened piece of road, and make sure it doesnt suddenly drive off the side over the curb. In http://ieeexplore.ieee.org/abstract/document/1248830/ they describe an algorithm which can be used to detect the curb by making use of photometry and range information, which is obtained by making use of stereopsis, i.e. using two cameras to get a 3d image. we can use this to "recognise" what the footpath actually is.

A different kind of footpath would be a footpath which doesnt have a road next to it:

in this case it is not necessary to detect a curb, as the scooter would just have to stay between the borders of the road. here it would be necessary to recognise this footpath is bricked, small, and has no road markings.

not finished yet

cycle path There exist a multitude of different cycle paths which have to be accounted for.

First of all, there is a cycle path next to a road, which has a white line, or a broken white line.

here a mobility scooter will need to understand the road markings, which are defined by the white line, and the image of a bicycle. for this we would need a camera on the scooter to recognise these road markings.

secondly, you have a cycle suggestion path, which is similar to a cycle path, but doesnt include an image of a bicycle and generally have a different colour to the main road (usually red).

cars, however, generally drive on these lanes more, which is more dangerous for a cyclist, or in this case, the mobility scooter user.

finally, you also have a cycle path which is completely seperated from the main road. These cycle paths are generally also have a red colour.

If a mobility scooter is on such a cycle path, there usually arent any markings, however since they are seperated from the road, it does not need such markings from a road. These cycle paths may be attached to a footpath, however these footpaths are raised and have a curb, as discussed earlier, and/or have a different colour to the footpath.

Conclusion
to find the differences between different road types we would need a setup to recognise different road heights, and road markings. a previous study has shown that a stereo camera setup can be used to find the curb, which can be used to recognise the side of the footpath. Furthermore, a single camera is needed for capturing road markings, and afterwards image processing is used to find road markings in the image.

Safety

Staying seated

The mobility scooter has to have a seatbelt and armrests to prevent the driver from falling out of the scooter when doing any sort of maneuver that does not necessarily result in the scooter falling. (12)

For extra safety the scooter should be able to detect if the seatbelt is being used and prevent driving when the seatbelt is not being used to further reduce the change of the driver falling out of the scooter. This could be done with a detection system in buckle of the seatbelt. ( Note that the user could insert the seatbelt in the buckle before getting seated. In this case this system would think that the driver has used the seatbelt, while that’s not the case.)

By adding a weight sensor in the mobility scooter, the scooter can detect if a driver is seated in the mobility scooter. If for any reason the driver falls out of the scooter, the weight sensor can detects it and act accordingly (stop moving). (18) The sensor should have a minimum weight it has to detect before the system concludes that the driver is present. The scooter should not think that the driver is present when, for example heavy groceries are placed on the seat and drive of without the passenger if the drive command is given accidently. If this limit is 30 kg, most objects placed on the seat should not activate the sensors, while it will engage if a person is seated. (22)

Stability

To minimize the chances of the entire scooter from falling the scooter has to be stable. In the research group of VeiligheidNL 94% of the people injured were using a mobility scooter with three wheels, the reaming 6% was using a mobility scooter with four wheels. Therefore the scooter should have 4 wheels. In most cases the accident occurred through an height difference between the wheels. Making sure the center of gravity of the scooter is as low as possible and as centered as possible, will make the mobility scooter more stable. Lowering the center of gravity also means that the scooter will be less likely to fall when driving on a sloped surface. (11, 21) ( This is something important to keep in mind when mounting extra equipment onto the mobility scooter)

Intervention

For the driver to be able to override the what the scooter is doing. The scooter should be able to detect when the driver is trying to override. The driver can steer in a different direction, brake, accelerate and/or change to reverse. Any of these actions can be done on purpose or by accident and any combination is possible.

All this while the scooter should also be able to take over from the driver when the driver makes a mistake.

( This is a complex topic, further exploration necessary. The combination of the driver being able to correct the scooter and the scooter being able to correct the driver can create a loop.) (13, 20)

Center of Gravity

For safety reasons, all four wheels should stay on the ground when making the mobility scooter is making a turn or when the mobility scooter is driving up or down a sloped surface of 10°.

Making a turn

Assuming a turning radius of R (m) ( the radius of the circular path the mobility scooter follow when making a turn as sharp as possible, distance up to the outer wheels), max speed v (m/s), a width of the scooter B (m) and the center of mass in the middle of the two wheels at height h (m).

When making a sharp turn the centripetal force will make the mobility scooter tilt, if this force is strong enough and lifts the inner wheel of the ground, the scooter will move back to the ground if the torque caused by the centrifugal force is smaller than the torque caused by the normal force of the tires still on the ground:

$\displaystyle{ \frac{m v^2}{R- \frac{B}{2}} h \lt m g \frac{B}{2} }$

Which means the height of the center of mass has to be

$\displaystyle{ h \lt \frac{g B (R- \frac{B}{2})}{2 v^2} }$

Or more general in case the center of mass is not in the middle of the mobility scoter:

$\displaystyle{ h\lt \frac{g B (R- (\frac{B}{2} + b) )}{2 v^2} }$

With b (m) the offset from the middle between the wheels.

B, R and v are known variables that follow from the different requirements that are set. While b will follow from the design that we choose.

Driving on a sloped surface ≤10°

The condition for the center of mass when driving up a slope can be calculated, just like the condition for when the scooter is making a turn. But in this case, the gravity will be causing the mobility scooter to pivot.

For the scooter to be in balance just after the wheels have left the ground:

$\displaystyle{ -l m g \cos( \phi)-h g m \sin( \phi)+ \frac{L}{2} m g cos( \phi)=0 }$

With L (m) the wheel base of the mobility scooter and l (m) the offset of the center of mass with respect to the middle of the center of the wheelbase, towards the wheel closed to the start of the slope.

$\displaystyle{ h \lt \frac{ \frac{L}{2}-l}{ \tan( \phi)} }$

L and φ follow from the requirements that are set. While l will follow from the design that we choose.

In the ideal case l would be 0 and thus the center of mass would be exactly centered. Which would result in

$\displaystyle{ h \lt \frac{L}{2\tan( \phi)} }$

legal requierements

Rules 1 trough 6 all have to do with speed limits. To be able to follow those rewuirement the mobilityscooter needs to have sensors that tell the current speed of the system and breaks to reduce the speed. It also needs to know ons what kind of road the system is currently driving. A side walk, bicyle paht or regular road and is this roade is inside or outside a built up area. The last thing the system needs to know is the speed limint on the road is is driving on.
TO DO eleberate on kind of sensors to use for current speed
TO DO navigation to use for kind of raods en current speed limits