28 January 2010
Interestingly, a web search turns up little information beyond citations. None of the titles in the citations indicate a successful implementation or breakthrough based on the work.
I still have a paper I wrote about the book and a description of a FORTRAN implementation that never got finished.
One of the challenges back then, and remains so somewhat today, is that testing ideas like this requires a simulation environment that can be as complex to produce as the actual ideas you want to test. But I realized that today I do have a physical device, my Create robot, that could be used for testing.
I'm not going to layout all the details of Cunningham's proposal since he took a book to develop and describe the idea. I won't even list the roughly 2 dozen specific assumptions in the model. What I am going to do is walk through some thoughts on how a project might proceed to see if it is worth pursuing.
You start with input and output elements - sensors and actuators in today's robot parlance. There are some reflex connections between these elements. For example, a pain reaction reflex so if an infant's hand touches something hot it jerks away. Or if the side of the mouth touches something the head turns in that direction in an attempt to suckle.
Jumping over the start up process (which is always a pain), lets assume the robot is moving forward and hits a wall. The bumper switch closes but there is no reflex to shut down the motors. The motors keeps turning and you get an overload reading. There is a reflex for this and it stops the motors. Now the motors are stopped and the bump switch is still triggered.
There would be a number of elements. Each sensor input on the Create could have an input element. Each actuator would have an output element. As indicated, the over current input element could be connected to an output element that stops the motors. Note - A point to consider that there might be output elements that don't directly connect to actuators but instead inhibit actuators. Continuing the thought, there might need to be backup, stop, and forward elements for the motors. In the situation described, these elements would have high levels of activity. Other elements, like a push button, would have no activity. The Cunningham model proposes that those elements with high activity are connected through a new memory element. The inputs to the input side of the memory and the outputs to the output side. What might happen is a connection is created between the bump switch, the over current and the motor stop elements through the new memory element. In the future, a bump switch closure would stop the motor.
I now recall one result from my work with the FORTRAN implementation. This is the need to have multiple elements to represent the state of input and output elements. My note above reflects this. For example, the bump switch needs two elements - open and closed. The motor needs forward, reverse and stopped. It may need even more indicating speed, although I would first try relating the element activity level with the speed.
The activity level of an element decays if it is not triggered. So the bump switch closing triggers activity that decays over time. The motor activity decreases until the motor stops. An issue would be to keep the bump switch closed activity going long enough for the over current activity to shutdown the motor and get the new memory element built. Note: maybe an input triggers again after a period of time?
How do we get the bump switch open? The only way is by getting the motor to reverse. Infants in a situation like this flail. They randomly move. Sometimes they do this happily while cooing and sometimes angrily while crying. It appears to be a natural reaction to try something, anything to make things different. (A really ugl phenomena in an adult but you still see it. If not physically at least mentally. Ever had a boss whose reaction was, "Don't just stand there! Do SOMETHING.") I don't recall the model addressing this situation. (I did find used copies of the book and have one ordered so I can refresh my thinking.)
Somehow some general level of activity has to increase which can generate activity at outputs. Sometimes this would be through inputs. For an infant this could be sound, pressure on skin, internal senses, and vision. I dislike simply generating random activity levels to cause something to happen. Maybe the general inputs of the Create - power levels, current readings, etc are sufficient to generate activity.
Clearly, a dropping charge level in the battery could be tied to a "hunger" reaction which sends the robot searching for its charger. That brings in using the IR sensor to control the drive for the docking station. That probably requires external guidance to train the IR / motor control coordination to execute the docking maneuver. That opens up an entirely different set of thoughts.
Which is enough for today... No conclusion on trying to implement this. But no conclusion not to do so, either.
27 January 2010
Remember I ported the code from the Command Module (CM) version to the Windows on the Fit PC Slim? In Windows there is a clock and in the CM there isn't. In the newer version I can setup a timeout by taking the current clock time and adding a delay. Then when the clock exceeds the timeout the timer has expired. For Trapped this meant the robot had not moved for over 10 seconds, despite other activities trying to make it move.
In the CM version, with no clock the Trapped needed to update the "clock" value to see if it exceeded the timeout value.
I'd say this falls under checking your assumptions. In the CM the assumption was that no clock existed so Trapped had to maintain its own. I didn't catch that the assumption was no longer valid in the Windows version.
I've been re-reading a lot of the papers on subsumption and the Jones book Robot Programming. I find that my implementation isn't really subsumption as it was originally presented by Rodney Brooks. Brooks is credited with the concept of programming robots by behaviors. His technique for implementing behaviors was subsumption.
My implementation is more in line with Jones, and also derives from David Anderson. David has an article about two of his robots, SR04 and jBot, which are accessible from the Dallas Personal Robotic Group .
I continue the discussion in a later post. I also want to take some time to reabsorb the subsumption and behavior programming concepts so I can elaborate on them.
26 January 2010
One architecture for robot software is called subsumption. It came out of MIT and Prof. Rodney Brooks who is a founder of iRobot who makes my Create robot. The idea is to break the robotos activities into small pieces. Let me build up the concept by example.
A fundamental activity of a robot is to cruise around. If nothing is to be done just let the robot drive straight ahead. So we create an activity called Cruise. It simply actuates the motors to go straight at a safe speed. It is easy to write and test.
After driving straight ahead for awhile the robot bumps into something. And continues to try to go straight ahead. This is not good for the robot or the cat or furniture it bumped into.
So we write a Bump activity using the sensors on the robot - the Create has a right and a left bump sensor on the front that wrap around a bit toward the sides. So Bump determines if a bump sensor was triggered the robot should stop. So we write Bump.
How to Bump and Drive get put together in the software? This is the subsumption architecture part. Initially its easy. First call Bump. If it doesn't activate, call Drive. If Bump does activate, don't call Drive.
Let this run. The robot goes merrily off, bumps into a cat, and stops. The cat gets up, the robot continues straight ahead, hits a chair, stops, and stops and stops and stops. Not very interesting.
What we'd like is for the robot to back up a little bit, turn, and then continue straight ahead. Hopefully that will clear the obstacle, and it will if the robot just brushed a wall. But even if it doesn't, repeating that behavior will eventually turn the robot toward an open area. (Well, many times it will. More later...)
This new behavior is somewhat different from Bump and Drive because we want it to do the back and turn without interruption. The term used for this is a ballistic behavior. Do we add this to Bump or Drive, or create a new behavior? The texts I've read added it to Bump. But based on my experience I create a new behavior called Flee.
Flee works with what could be called an internal sensor. This internal sensor tells Flee thow much to back up and turn. So Bump sets this internal sensor to backup a little bit (40 mm) and turn a little (20 degrees). Since Bump can tell whether the left or right bump sensor (or both) was hit it also sets the direction of the turn so the robot will turn away from the bump.
Now the activities are called in the order: Flee, Bump, Drive.
Remember that if Flee is active the later activites aren't called. If Bump is active, Drive is not called.
So the robot Drives ahead, Bumps into something, the internal flee sensor is set, and Flee backs up and turns the robot. Then with both Flee and Bump inactive, Drive engages and the robot moves ahead.
Just for completeness, I have another activity called Trapped. It is added between Flee and Bump. Every time Trapped is called it records the time and distance moved. If the robot has not moved very far (80 mm) in a certain period of time (10 seconds) then Trapped sets the flee sensor to back a little bit and turn 180 degrees. The idea is that by turning 180 degrees the robot can get out of a bad situation. One such situation is the legs on a rolling desk chair, or a corner.
With these behaviors my Create wanders around the house pretty well.
The actual implementation needs a couple more details. Here is some psuedo code:
preempt = false;
preempt = Flee(preempt);
preempt = Trapped(preempt);
preempt = Bump(preempt);
preempt = Drive(preempt);
The variable preempt is set to true by an activity if it is active. If Bump sense a bump then it sets preempt. When Drive sees preempt is set it does not activate, i.e. does not drive forward. If Bump sees preempt is set it does not bother checking the bump sensors, because presumably Flee is now handling the bump condition.
Why bother calling activities if they are preempted? Look back at how Trapped works. It is monitoring the distance traveled. If it is not called because Flee is active...
And there I'm going to let it hang because I don't remember why. But I'm going to publish this now, leave it as is, and resume in another posting.
This is software development as it is, folks. There are a few possibilities here:
- I simply don't recall the reason so have to remember it or rethink it. That is why you should document things.
- There was a valid reason that is no longer valid. Boy, that happens all the time in development. A good habit to develop is to revist assumpts regularly to see how they've changed.
- I simply blew it when writing the code many months ago.
- ...or some totally different situation that I can't think of right now.
That is the basics of subsumption, though. A good book on robot programming that covers subsumption is Robot Programming - A Practical Guide to Behavior-Based Robotics" by Joseph L. Jones.
25 January 2010
The main platform is the iRobot Create. It is an autonmous robot by itself but provides control through a serial port connection using a protocol called the Open Interface (OI). The OI can read the sensors and control the actuators of the Create.
The Fit PC Slim is a compact, low power PC with 3 USB ports and a Wifi, plus the usual PC components. It is powered from the Create through a voltage regulator on the Interface Board (IB). The IB also carries the USB interfaces for the serial port and I2C.
The reasons for the Wifi on the Slim is to download software and allow monitoring from the desktop or laptop, especially in the field.
RoboRealm (RR)is a software package whose main purpose is vision processing. It also has a lot of robot control capability, including a plug-in for the Create. I decided not to use that plug-in after some issues figuring out exactly how it worked. That may have been a mistake. My other concern was the latency of getting sensor information with it getting collected by RR and then collected from RR by the control program. RR will be used to handle the camera and vision processing.
First lesson is that the Create doesn't provide unswitched power that is sufficient to run the Fit PC Slim. If the Create is turned on there is sufficient power. This means the Slim can't turn the Create power off because the Slim loses power, also.
Ideally the Create can stay on all the time. It has a docking stations - its home base - for recharging. The built in processing can find the base and run onto it to charge, or my software could replicate that processing.
First minor glitch is that the Create stops responding to the Slim commands when it docks. It turns out there is an undocumented soft reset command (a '7') that puts it back into a mode where it will accept commands. Once back into this mode the Slim can monitor the charging process and determine when it is safe to leave the dock.
When the Create is charging is a good time for doing work on the interface board or the Slim. What happens when you reconnect everything onto a charging Create?
The (re)learned lesson is that startup and shutdown processing are often the most challenging parts of a software project. Once everything is up and running a software process is usually straightforward, albeit with a lot of details to chase. You just nibble away at them one at a time until they are all resolved. Then the process is just doing the same thing over and over again.
Startup is a big discontinuity. What was the robot doing before it shutdown? What has changed since then? What is the current state now?
This all was triggered when I realized the robot had to determine whether it was charging or in the wild when it started up. It takes different actions depending on where it is. If docked it continues until charged, backs off the dock, and switches to "wild" mode of operation.
Okay, who said, "Rud, as an experienced developer you should have dealt with this already." Guilty as charged but this has been a casual, hobby project up until now. This was my wakeup to start applying a more formal approach and thinking through some of these issues. I'm still not going to go fully formal since I'm more interested in having fun. So don't expect a 6 week hiatus while I produce a formal analysis and design. I am going to do some of my thinking in blog posts, using it for my documentation.
The report from the ADC2 was that 50% of the testers in phase one liked the game so it seems well worth the effort to submit it to the market.
I also got a Command Module (CM) which fits onto the connector. The CM is an Atmega 168 processor that adds some additional I/O. It can be programmed to control the Create. I did so and basically reproduced the wandering behavior of the Create. It move around, bumps into things and turns away from what it hit. I added some additional behaviors such as if it got trapped, i.e. caught in the same place for a period of 10 secs, it would move to extract itself.
I want to do more with robots, such as entering in a RoboMagellan contest. That requires an outdoor capable robot that does a lot more than bump into things. A key component to me is vision. Maybe I could do that with the CM and another processor (like the CMUCam) but I really didn't want to learn YAPE (yet another programming environment).
Around the time I got thinking seriously on this I looked at ITX boards. Then the Fit PC computers became available, specifically the Fit PC Slim. The PC form and wireless sold me on trying to us it. The one drawback might be the processor speed when trying to do vision processing. That is acceptable because the Create with the Slim is a testbed for RoboMagellan where an entirely new, slightly larger platform will be used. By going with the PC as the base there are a large number of possibilities, including laptops and netbooks. If the processor is slow for vision the Create simply won't move as quickly or smoothly.
I have the Slim hooked up to the Create, drawing power, and running most of the behaviors previoiusly implemented with the CM. Once I got the basic threading, serial communications, and Create interface working the behaviors started working within minutes since they ported easily from the CM versions. All the code is C++. Threading and serial port routines are all from previous projects so its all come together with a few days work.
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