User Manual - Actor-Lab
Contents
1. actor lab user manual July 04 INPUT ma aes OUTPUT CONTROL turnup turn down ACTOR When on dictoris awake if con send meag on receiving the mesenge BEGIN Add s Mevage Eeli Line idh o Boley Mariabie belay Send to EM the message EN EE Send boo up the me weak Current interface and editor 2004 actor lab user manual July 04 2 How actor lab works e The key idea to understand is input gt process gt output object input AS data flow event J Poi analogue battery switch attery level device level repeat trip mode analogue mode screen device button trip mode Power definable OFF Fig 1 The different types of objects in actor lab e The basic cycle of actor lab involves real world events being transformed by the INPUT OBJECTS and sent as messages or as a flow of data to PROCESS OBJECTS e PROCESS OBJECTS in turn create a flow of messages to each other and on to OUTPUT OBJECTS e OUTPUT OBJECTS then bring about real world events actor lab user manual July 04 Important details actor lab works on Mac OS 9 amp OS X and on PC Windows 98 2000 amp XP actor lab application has to be in a folder with projects sounds etc double click actor lab application to begin to quit application Command Q on Mac Control Q on PC click to open objects objects have to be given a unique name to appear in the message list of other objects if a name is keyed in that2. has already been taken the name will revert to whatever it was before if the name of an objects is changed e g to correct it s spelling any reference to the name in the scripts of other objects is changed automatically hold alt down to move objects around overlapping objects are grouped and only shown as having one input output path hold alt down and drag on darkened overlap area to move grouped objects around hold alt down to drag objects out of a group alt click on background to dim brighten paths alt click to open up screen buttons at the bottom of the display serial port selection under OPTIONS plus advanced mode scripting load save under PROJECTS click on the lights for info cycle time improved by disabling inputs the POWER OFF button turns off all outputs and sends a forget message to all actors a project file renamed as default actl and put in the default folder will override the default new configuration hold the alt key down as you click on NEW PROJECT to be able to configure the input and output objects to have a switch amp light on the same input to use a temperature sensor to monitor the battery voltage change the number of actors counters actor lab user manual July 04 3 Linking to the RCX e actor lab requires a serial RCX tower connection it can be via a USB serial converter e the serial port selection is under OPTIONS e the RCX brick must first have the RoboLab firmware downloaded to
3. more difficult problems it is necessary to understand more about event sequencing and also a little about an important issue for control robotics task prioritisation These are dealt with in section 7 13 actor lab user manual July 04 5 2 counting actors Rather than just responding to to BEGIN messages counting actors respond to changes in their value a number between 0 and 9999 They constantly compare their value with a target value which can either a fixed value or another counting actor When the value matches ie it is greater than equal to or less than the target counting actors send messages on much like other actors ACTOR Counting LESS THAN When it is awake and the value is EQUAL auTO Fixed Value 9 5 fo to the value selected then a counting actor CREATER THAN a con send one or mom messages to actors Add Message Delete Line Add a Delay Variable Deleg Send to FUME the message sicep FOUAL GREATER THAH The value that a counting actor has is set by messages from input objects and other actors using the arithmetic operator messages that can only be sent to counting actors Another way that a counting actor can be used is simply as a value a variable in messages sent by other actors The value could be e sent to other counting actors e used to set the speed of motors e used to control the flashing rate of lights e used to control the time delay of a message See the tim
4. actor lab user manual July 04 actor lab User Manual Peter Whalley amp Ben Hawkridge KMi The Open University OUTPUT bert on line laft motor right sensor right on kine right motor EE CONTROL forwards de up Y speed up el C6 turn dian Speed doan actor lab user manual July 04 Disclaimer Actor lab is made freely available for any non commercial use The software and documentation are the copyright of the Open University but may be copied and distributed freely provided that no change is made to them No fitness for any purpose is claimed for actor lab and no responsibility is accepted for its use No guarantee of any support explanation or guidance as to the use of actor lab is given LEGO RCX and RoboLab are trademarks copyright the Lego Company RoboLab was developed by Tufts University No connection of any kind with either the Lego Company or Tufts University is implied or claimed for actor lab or its authors Contents 1 Introduction 2 How actor lab works 3 Linking to the RCX 4 Input objects 4 1 analogue devices 4 2 switches 4 3 buttons 5 Process objects 5 1 actors 5 2 counting actors 6 Output objects 6 1 motors 6 2 lights 6 3 sound 7 Process control 7 1 event sequencing 7 2 task prioritisation 8 Classroom use actor lab user manual July 04 actor lab user manual July 04 1 Introduction Overview Actor lab was design
5. ait seconds then send tolght the message lazh Wait 12 seconds then send to icht the message top hashing The flashing rate can also be assigned to any named counting actor 16 actor lab user manual July 04 6 3 sound OUTPUT Sound Sound will play the selected sound file messages from actors PLAY plays the selected sound PLAY LOOPED repeatedly plays the selected sound STOP stops the sound Any aiff sound file placed in the Sounds folder will appear in the menu the beep sound is the current system beep 17 actor lab user manual July 04 7 Process control 7 1 event sequencing Actor lab is a time based language All processing takes place concurrently as far as the the user is concerned as each actor has its own process thread Consequently messages that are not delayed are all sent at the same time It also means that each actor effectively has its own clock and script messages that are to be delayed are individually time stamped with respect to the event that initiated them and sent at the appropriate time Unless meta commands cause the actor to be disabled at the time that the message should be sent It is easy to create a sequence of timed events in actor lab but it is very important that users understand that all the delays in a script are with respect to the original BEGIN message Because the script is of necessity an ordered list and the editor keeps it in order
6. ed to make the teaching of control technology possible in classroom settings where after a general introduction by the teacher year 5 7 children are able to work by themselves in small groups with only peer support The language and the interface were designed to represent the notion of input process output that is central to basic robotics and control technology BECTA 2004 Actor lab is a control language based on the idea of asynchronous message flow and represents a simplified graphic version of the actor programming model It s operation can be explained using the intuitively accessible model of a cast of actors able to send messages to each other with the programmer as playwright Concurrent processing identified by Papert 1980 as a fundamental feature of control languages is implicit and a real time visualisation of process states and message flow is provided by the actor lab system Serialisation sequencing of events is effected by time based messaging and suppressive control of objects task prioritisation is achieved with object meta commands Background The theoretical ideas underlying actor lab are derived from the event driven message passing computer languages that began with the actor based languages devised by Hewit 1976 and further developed by Agha 1986 Practical inspiration was provided by HyperCard and to some extent by Lab View The first version was developed in HyperCard Whalley 1992 but the problems as
7. en additional commands are made available not advisable in the first session with Year 5 children A SLEEP message will cause an actor counting actor to become dormant a condition in which they will only respond toa WAKE message Whilst dormant any delayed messages will not be sent If the actor counting actor receives a WAKE command it becomes active again but only on the next process cycle ie 0 05 sec later If WAKE and BEGIN are to be sent by the same actor then the following syntax is necessary send to the message Wait e e G CUT round BUGGE e begin A FORGET message deletes the stack of delayed messages In the case of a counting actor all three message stacks are deleted Examples In this example load line buggy foil the left and right sensors have their trigger level set so that they send a BEGIN event to the actors left on line and right on line respectively as they move over the black tape The right sensor is also set up to send a stream of data to the counting actor light level 20 actor lab user manual July 04 ACTOR Counting When it is awoke ond the volue is GREATER EQUA U siver awai than the value selected then o counting GREATER achor con send one or more messages fo octors Add a Message Delete Line Add a Delay Woriable Deloy Finish light level SRS turn round Bulges id begin The counting actor light level is set up so that when the value of the da
8. ensor At one secend intervals the Light Senor Light level OOo can send one or more messages to right sensor M N Light Source Add o Message Delete Line Finish TRG aca light level the message REPEAT Disable any unused inputs to improve the response time The minimum time is 0 15 sec for one input which could have both a switch and a light sensor attached The battery level is only sampled every 5 seconds and has little effect on the response time The increasing parameter is only useable with high charge rates 11 actor lab user manual July 04 4 2 switches Switches can send a message or messages as they are pushed in or when they are allowed out in ON out OFF The icon in the edit window changes to show the current state of the switch INPUT Open Switch Dtscle Sensor input 1 When it is switched OFF the switch can send one or more messages to Actos 4 3 buttons There are 7 user definable screen buttons plus a Power OFF button The POWER OFF button turns off all outputs and sends a forget message to all actors alt click on the definable buttons to open their edit window The user definable buttons can send one or more messages but they can not be delayed It is possible but not really advisable to send messages to the screen buttons Power OFF turn left forwards backwards 12 actor lab user manual July 04 5 Process objects 5 1 actors Unders
9. er and line buggy variable demos for examples of these uses The sensor ANDing demo shows the most complex use of a counting actor 14 actor lab user manual July 04 6 Output objects 6 1 motors It is usually a good idea to test out motors in order to discover the relationship between clockwise anticlockwise and up down forward backwards etc OUTPUT Motor A moter can respond to the following messages from acorn __eruaher CLOCK WISE makes the moter turn clackwise ANTICLO CK WISE makes the moter turn anti clockwise STOP Ue lbo molor BRAKE motor is hard fo turn If any counting actors have been given names then they appear below the fixed speeds as a possible parameter See line buggy variable demo Scam crusher the message speed 1 speed 2 speed 3 speed 4 speed 5 speed 6 speed 7 v speed amp 15 actor lab user manual July 04 6 2 lights It is possible to test out light objects by clicking on them OUTPUT Light A light con mspond to the following meiszages from actors ON tums light on OFF tums light off FLASH E makes the light flash ot selected rate STOP_FLASHING stops the light Hashing It is important that the messages be paired correctly stop flashing does not cancel on and off does not cancel flash Send to light the message on Wat 3 seconds then send to light the message oif W
10. ess importance than the than the ability to work in whole class setting within the 4 actor lab user manual July 04 middle school The internal cycle time of the system and the display refresh time is of the order of 0 05 sec However each input object which may represent both an analogue device and a switch takes approximately 0 15 sec Whilst it would be unwise to attempt fly by wire control with actor lab such benchmark robotic tasks as maze and line following are easily achievable References Agha G Actors A Model of Concurrent Computation in Distributed Systems Artificial Intelligence Series MIT Press 1986 www becta org uk subsections foi documents technology_and_education_research control_technology pdf Hewitt C Viewing Control Structures as Patterns of Passing Messages AI Lab Memo 410 MIT 1976 Papert S Mindstorms USA Basic Books 1980 Whalley P Making Control Technology Work in the Classroom British Journal of Educational Technology Vol 23 3 pp 212 221 1992 actor lab user manual July 04 on mousellp i if the icon of me 148 then exit mousellp set the Flite of me to true start your script here turn red on turn omber off turn green off put inte card field counter a delayFor 1 secs then send mousellp to button startHolk delayFor 18 secs then send mousellp to button checkCars set the hilite of me to false end mouselp E ee Original interface and editor 1992
11. if delay timings are changed it is possible to misread the delay times as having a cumulative effect The 3 lights demo is quite effective at communicating the correct interpretation It is possible that colour banding of at the same time messages might be introduced at some stage ACTOR When an Ador is awoke it con send massages on receiving the message BEGIN Add a Delay Send to EE the message play Send ta light the message on Wat 4 seconds then send te light the message off seconds then send te laut lt the me amp then send te light 3 the message ol 4 the message on 1 send to light 4 the message oi amp then send te horn the message riy Sound beep BEGIN 18 actor lab user manual July 04 Complications that most users do not need to know about An actor can be repeatedly fired even while it has messages that are waiting to be sent The effect is that any delayed messages would be added to the stack with a new time stamp and any immediate messages would be sent straight away This is likely to have unwanted consequences which can only be avoided by controlling the input of messages to the actor See the debouncing effect in the timer demo and look at the script in the SET actor of Car Park 4 for ways to overcome any problems The underlying processing is of course not actually concurrent but has been designed to appear so to users controlling slowly moving m
12. it e actor lab requires constant communication with the brick ie vertical RCX for a buggy see the maze amp line buggy manuals e 4 green lights showing indicates that you are connected to a brick Tower Responding RCX Responding Sensors 2g6ms Connected Error RCX click to see this gt e click on the background to hide the RCX tower extra info panel e disabling unused inputs is the only way to improve the response time e actor lab will work in a screen mode when not communicating with a RCX brick try the timer demo 10 actor lab user manual July 04 4 Input objects 4 1 analogue devices Light and temperature sensors can send a message or several messages when their input level falls below or rises above the value set by the slider Clicking on the input object opens up the edit window and turns on any output light source associated with the sensor See the crusher amp car park demos Avemge Volue Disoble Sensow Input 3 INPUT Light Sensor When the light level drops below the Light level level you set OFF the Light Sensor con right sensor BP Rt ee ed Light Source Add o Meirage Delete Lime TECE right online Eutectic begin Light and temperature sensors can also send a stream of values and other messages with a 1 second repeat cycle See the line buggy and sensor ANDing demos Average Walwe Disable Sensor Input 3 INPUT Light S
13. lab was designed to be used by a teacher working with a whole class and having to rely on the children to help each other to a large extent An advice system has been developed to help identify problems but is not yet ready for release A set of problems with student manuals can be found at http actor lab open ac uk The manuals are initially fairly directive but become more open ended They have had two years of trials with year 5 7 students It is probably best to introduce the key ideas to the whole class with a system connected to an overhead projector to get over the key ideas e the input gt process gt output model e the programmer as playwright developing scripts for a cast of actors The Year 5 topics cover controlling machines and making them safe the Year 6 topics introduce machines that react and the Year 7 topics develop the idea of machines that can find their way around
14. odels The underlying cycle time of the system is 0 05 sec and each actor is then processed in a random order It is possible but difficult to achieve indeterministic results if messages are passed between actors with no buffering delay The 0 1 sec delay was added to solve any problems The minimum delay used in normal user programming is 1 sec and so the particles indicating message flow are timed to take 0 9 sec Turning on the slow messages condition causes messages to be visible as a ripple through the actors see the cascade demos but of course makes control of real world events problematic This condition is useful in debugging some logical problems particularly those concerned with event prioritising v Show Messages Slow Messages Allow Sleep Wake Variable Delays Select Serial Port eros me click gt 19 actor lab user manual July 04 7 2 task prioritisation Beyond a certain level of problem complexity it becomes necessary to constrain the concurrent operations In procedural control languages e g RoboLab MindScript NQC this is achieved by setting task priority levels or by creating an overriding subsumption architecture In agent actor languages e g MultiLogo actor lab task prioritisation is achieved by the suppressive control of objects ie actors can send and be sent meta commands that change their state If the Allow Sleep Wake condition is checked th
15. sociated with having to input scripts via the HyperCard editor meant that it was only useable with year 7 children The current graphic interface avoids any problems with syntax errors and was developed using Macro Media Director by the second author School based testing has led to improvements in the graphic interface particularly with respect to the visualisation of message paths and event data flow Also a set of documented examples have been developed and tested with year 5 7 children These involve controlling and making safe a crushing machine controlling a car park barrier which involves counting cars in and out and programming a buggy to move through a maze and follow lines Limitations A severe limitation of most control languages particularly those using the Lego RCX brick is that once the program is downloaded little or no information is available to help children understand why their programs do not work as they had expected This makes it difficult to arrange for children to work by themselves and usually entails providing a great deal of adult support Actor lab overcomes this problem by maintaining a constant link with the RCX A dynamic interface gives information on the state of the input and output conditions and of even more importance the internal processing in terms of message flow This tethered operation can only be achieved at some cost to the overall response time of the system but this is of much l
16. ta stream goes higher than the value in the counter actor silver level it will send a BEGIN event to the actor turn round The messages in actor turn round make sure that all the actors that might respond to a changing light level are disabled before the right turn is initiated After the sensors have safely passed over the foil and black tape they are enabled again See the web site for video ACTOR When on Actor is owake it con send _ me messages on receiving the message turn round BEGIN Add a Mespage Delete Liner Add o Delay Vorieble D Finish RREN rightaniine Moea seep send tolei on ine the mez e sleep Send te light level the message oop lal 05 Wait 05 seconds then send to right Wait 8 seconds then send to left on line Wait 4 e the m wy ait Se zeng to the mes 21 actor lab user manual July 04 8 Classroom use Control technology robotics is a highly motivating and rewarding part of the curriculum for students Unfortunately it is quite difficult to teach in the whole class environment with normal levels of support and equipment Actor lab and the exercises described here have been designed to overcome some of these problems The ideal way to discover control technology robotics is to build a model and then learn how to control it by experimenting and this is quite possible in the context of after school clubs with extra adults around to help the teacher Actor
17. tanding how the actors operate is the key to working with actor lab The best metaphor to present to children to describe how they are going to develop their programs is to think of themselves as writing a play giving each actor a set of messages a script to carry out Clicking on an actor opens up the edit window that allows you to enter the script If you hold the alt key down whilst dragging on an object you can move it around Messages from input objects are shown in blue from other actors in yellow and from buttons in grey Messages to output objects are shown in red When actor lab is working which is all the time that the edit window is not open you can see the messages being sent as particles moving along the lines ACTOR When an Ador is awoke it can send messages on receiving the message startup Tae Add o Message Delete Line Add a Delay Variable Delay EGA horn LUE play sound Horn Honk Wait seconds then send to the message To begin with it is best to think of actors as simply responding to BEGIN messages which cause them to send BEGIN messages on to other actors or specific messages to output objects e g to turn on a light The only complication at this level is that messages can be sent on immediately that the actor receives a BEGIN message or after some delay Reasonably complex control problems can be tackled with no more knowledge than this e g Crusher Tasks 1 5 and Car Park 1 2 demos For
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