Feedback Systems and Driving Clinton Matney AT Workshop

Feedback Systems and Driving Clinton Matney AT Workshop 2016

Design Principles Related to Driving Controls • Compatibility between stimulus and response – Hazard warning sound – i. e. lane change warning • Where should the sound come from to get the desired steering correction? • What sound is most likely to get the desired response? • Continuous vs. Discrete Signal – – Temperature measurement example to adjust thermostat • Gain – basic ratio of input to output – Also related to effort required to operate (high gain = use a little effort to control a lot) • Size and shape of control – Why is a steering wheel a wheel? • Lag – time differential between input and output – RC Car example

Open Loop vs. Closed Loop Control System • Dryer example – Timed Mode (open loop) • Once you turn the dryer on it will run until the timer is finished. • It doesn’t matter how wet or dry the clothes are • Power wheelchairs are another example of an open loop system – the joystick controls rate/speed – “More” or “Less” dry Mode (closed loop) • Dryer runs until the desired moisture level is achieved • Dryer continuously measures the moisture and shuts down based on the feedback from the moisture sensor • Closed loop systems are also referred to as position controls – the position of the input is always associated with /relative to the output.

Open Loop vs. Closed Loop Control System • Demonstration Device - Brake – Mechanical linkage: show force required at pedal and at handle • Purely mechanical system • Not much mechanical advantage • Mechanical gives you feedback – pushes back against me – resists my movement – closed system

Open Loop vs. Closed Loop Control System • Demonstration Device - Brake – Power assist control system • Still have mechanical linkage – just making it easier at the handle • Reducing effort to operate the control, but range (distance) is the same • Closed vs. Open : – A power assist system with NO effort would be like an open system – but some level of effort is built in on purpose » springs help you control the system – provide feedback » Otherwise, as soon as move handle, the mechanical linkage is worthless

Open Loop vs. Closed Loop Control System – Now, powered assist control system, and take down to zero effort steering • Still mechanical linkage, still same range, just a lot less effort • Reduced (Minimal) feedback

Open Loop vs. Closed Loop Control System – Full power – no mechanical system – full servo control • Powered system with no mechanical linkage – remove a lot of feedback, but you are no longer constrained by range. • A larger range can help compensate for loss in feedback – it takes a larger movement to get the same output movement of the brake. • A shorter range will cause it to be very difficult to precisely control the brake – a small movement causes a large change in the movement of the brake.

Open Loop vs. Closed Loop Control System • Demonstration Device - Brake • 4 different demonstrations • Consider controllability when trying to be precise with each option – Increase range over mechanical option – About same as with mechanical – Joystick territory – moving handle 1” to get the same distance you did before – Add Feedback – spring with full power system

Feedback while Driving • Visual – Passing scenery – Other vehicles – Road signs – Lights/Gauges in the car

Feedback while Driving • Auditory – Turn signal noise – Engine noise – Sounds from other cars • Warning beepers • Horns • Engine noise

Feedback while Driving • Tactile – “Feel” the road – Effort to turn steering wheel – Feel grinding of wheel bearings

Feedback while Driving Michael’s test driving experience: 2016 Chevy Volt • Can’t hear engine noise while running (electric or gas engine) • Electronic Power Assist provides a “soft” steering feel – little effort to turn wheel • CVT (continuously variable transmission) 2005 Ford Mustang GT • Use engine noise to gauge speed • “Traditional” hydraulic power steering Harder to turn the wheel – requires effort • 5 speed manual transmission: Feel the engine shift

Reduced Effort Steering • Standard passenger cars: – Steering is purely a mechanical system: • To decrease the effort, you have to increase the range through which the control (steering wheel) moves • For example – you could increase the number of revolutions required or increase the size of the steering wheel • Standard passenger car around 15” steering wheel • 2. 8 – 3. 3 revolutions full left to full right • Total wheel deflection is about 40 degree deflection of front wheels • Varies somewhat based on Ackermann steering geometry – Range and effort are designed around our ability to operate the control – considering strength to operate and range of motion required.

Reduced Effort Steering Now, add a disability – – Reduced strength – Reduced ROM • Steering modifications in vehicles – Replace steering wheel with smaller diameter wheel – i. e. 10” • Results in decreased sensitivity of steering system • further my control device moves, the more finitely I can control what moves – Replace steering wheel with joystick • 1” total movement of steering control results in relatively larger deflection of wheels with very small movement. • Electric Power Assist Steering allows for some control over the “feel” of the steering while maintaining ease of effort with reduced range.

A word about lag • RC car – lag • Increases difficulty in controlling a system when there is too much lag. • Some is not necessarily a bad thing • The motor EMC uses is a set speed – motor at full power will only turn so fast, I can turn the wheel/joystick faster than the motor will turn. – This is not something that would happen in normal driving

Why driving a joystick is so hard • Steering wheels are position controls. – the wheels correspond to the same position in the range (if I am 5” to the right of center, the wheels will be specifically in the same place every time) • Joysticks are really rate controls not position controls – Joystick doesn’t control directly where the wheels are, it controls the rate at which the wheels are turning, so the position of the wheels doesn’t relate directly to the position of the joystick • Adapted Driving Control manufacturers can “shape” the output of the joystick • The first few degrees look just like a position control. But beyond there – the joystick looks like a rate control.

High Tech Driving System EMC • Size and shape of control– Smaller range of deflection – just the joystick – Not “as” rotational – just joystick rotates • Completely servo system – No relationship between effort of control to the output • Can “outrun” wheel with joystick – lag – not in normal operation Joysteer • Size and Shape of Control: – Rotational feature of control wider degree of deflection – almost double – Rotational - whole controller rotates below your hand – using different muscles • Completely servo systems – Joysteer feeds the effort to turn the wheels back to the joystick in a given percentage • Whatever max speed is on motors, they keep you from being able to move joystick until the wheel is with the motor – can’t outrun it.