Intelligent Robotics I: Servo Control

Overview and example of robot control

Jeff Allen

Robot Recipe

• Sensors– Artificial (sonar, cameras, temp, light, water,.......you

get the point)– Human (From a controller perceiving a worthy input)

• Intelligence– Artificial (computational, search, genetic, NN, cellular

automata, … too name a few) – Human (a controller intelligence varies in extremes,

and is both time and subject variant)

• Actuators– Artificial **(this is a requirement)

Robotic System The world and the boxes

Sensors Input Intelligence

Robot HW/SW State

Robo world

• Sensors– Can exist solely in

either domain– Can exist in mix of

both• Intelligence

– Can exist solely in either domain

– Can exist in mix• Robot State

– Internal conditions used to represent actions

• Actuators– The method the robot

interacts, injects it’s will onto the real world

Actuators Output

Robotic System: simplification

Sensors Input Intelligence

Robot HW/SW State

Robo world

• Input to Intelligence– Ignore all outside

possibility as it is not in the system

• Intelligence to Robot State to Output– Imply state as

part of the connection

Actuators Output

An Abridged Robotic SystemTransistions and related factors

Sensors Input Intelligence

Robo world

• Input to Intelligence– Complexity of

sensor input– Must travel in

robot world even if remote controlled.

• Intelligence to Actuators – Must travel in

robot world

Actuators Output

Sensor Information Complexity (Artificial)

• Simple– Touch– Sonar– IR– Light– Temp– Engine and systems feedback– Radio signal– etc

• Middle to Upper Complexity– Sonar Arrays/Radar Arrays– LIDAR– Camera(s)– GPS Positioning– Etc

Consequences of increased sensor information complexity

• Information size• Processing difficulty• Usefulness of data may require many

different processes • Yet another etc….

• All ultimately lead in one way or another to increased requirements of the robot system. Which usually means $$$$!

Information Traveling in the Robot World

• Information and it’s communication must happen.

If nothing is communicated how can it be a robot?

• We all know how it is done.Electrical signals and representations sent to devices program to respond accordingly.

Some robot system methodologies

• Single autonomous unit– All onboard system intelligence is onboard. With

remote communications generally limited to system reprogramming or goal adjustments. Not direct actuator control.

• Remotely controlled units– The controlling unit, human or artificial, is located at

another location controlling the unit.• Mixed units

– Remotely controlled units with certain automated subsumbtive responses controlled directly. Example robotic overrides, like your brakes

More about robot system methodologies

• Single autonomous unit– Varying complexities based on onboard computational and

sensing abilities as well as actuator device complexities.– Complexity increases are expensive and can create extremely

difficult systems in situations where onboard requirements are stretched to limits

– Excellent response times are possible• Remotely controlled units

– Onboard equipment requirements are lessened with respect to computational devices. (less expensive)

– Complexity increases due to sensors now increase bandwidth requirements, but are otherwise less expensive.

– Natural lag in response related to communicated distance as well as bandwidth

• Mixed units (see all above)

PC remote controlled systemsToday’s example

• Inexpensive.– PC (look at a Fry’s ad)– Servo controller board ($10 - $200 on average)

• Potentially Powerful– Information communicated can be communicated

along multiple channels: usb, serial, firewire, etc..

• Numerous programming languages to choose from.

• Why do we use them? Look above

Review: Traveling in the Robot World.

what did we say?

• Information and it’s communication must happen. If nothing is communicated how can it be a robot?

• We all know how it is done. In theory. Practically?

A communicating example:A PC controlled robot

Communication Channel PC to Control:

In this case RS232

Our development environment:

Visual StudioVB 6.0

Input to PC:

Predefined movement scripts / Sensors

Actuator Control:

ASC 16 Board

Communication channel:PC to RS232 piece

• MS Visual studio provides the MSComm object capable of:– Transmitting/ receiving / open / close to a comm port using rs232.

The requirement is only that the data be presented in the format it is to be sent according to receiving device.

• ASC 16 has specific commands for each servo device.– Each servo is capable of 180 degrees of movement with a

precision of 180/4000 degrees/point, .045 Deg/point– The ASC16 is capable of simple position commands ,small loop

programs as well as positional feedback (not in this example)– Commands are given in 1,2, and 3 byte packages

Example goal

• We need something to convert commands from the PC to appropriate ASC16 commands, a translator.

Requirements

• Each servo device will have a different range of motion and rarely will move all 180 degree.

• Each device is a separate entity, interrelations can be calculated but otherwise do not exist

ASC16 Commands• ac (81-96 DEC) (51-60 HEX)• Acceleration• am (250 DEC) (FA HEX)• Abort All Motion• at (249 DEC) (F9 HEX)• Abort Triggers• bt (124 DEC) (7C HEX)• Base Time• en (121 DEC) (79 HEX)• Enable Module• f+ (251 DEC) (FB HEX)• Freeze Motion• f- (252 DEC) (FC HEX)• Freeze Motion Off

ASC16 Commands (cont.)• fp (21-36 DEC) (15-24 HEX) • Flyby Position• iv (112 DEC) (70 HEX)• Invert Servo Coordinates• la (242 DEC) (F2 HEX)• Load All• ld (123 DEC) (7B HEX)• Load Default Position• lm (253 DEC) (FD HEX)• Loop Marker• lp (254 DEC) (FE HEX)• Loop• mk (221-228 DEC) (DD-E4 HEX)• Marker

ASC16 Commands (cont.)• mr (41-56 DEC) (29-38 HEX)• Move Relative• mk (221-228 DEC) (DD-E4 HEX)• Marker• mr (41-56 DEC) (29-38 HEX)• Move Relative• mv (1-16 DEC) (01-0F HEX)• Move servo absolute• no (0 DEC) (00 HEX)• No Operation• no no no (0,0,0 DEC) (00,00,00 HEX)• Terminate• nv (113 DEC) (71 HEX)• Non-invert Servo Positions

ASC16 Commands (cont.)• op (110 DEC) (6E HEX)• Output• pg (120 DEC) (78 HEX)• Program Module address• ra (141-148 DEC) (8D-94 HEX)• Read Input as Analog• rd (179 DEC) (63 HEX)• Read Inputs as digital• rp (116 DEC) (74 HEX)• Report Position• rs (117 DEC) (75 HEX)• Report Speed• s+ (245 DEC) (F5 HEX)• Servos On

ASC16 Commands (cont.)• s- (246 DEC) (F6 HEX)• Servos Off• sa (241 DEC) (F1 HEX)• Save All• sp (61-76 DEC) (3D-4C HEX)• Speed• st (151- 168 DEC) (97 - A8 HEX)• Stop• sv (122 DEC) (7A HEX)• Save Default Servo Position• tl (119 DEC) (77 HEX)• Trigger Level• tm (181-196 DEC) (65-C4 HEX)• Trigger on Motion Completion• tp (201-216 DEC) (C9-D8 HEX)• Trigger on Servo Position

ASC16 Information:Command Set Example

mv (1-16 DEC) (01-0F HEX) Move servo absoluteFormat: mv$ position mv$ = 1-16 for servo 1(mv1) to 16

(mv16)position = 0-4000Description: Moves a servo to a new absolute position at

the speed and acceleration rate set for the specified servo.

Example:Mnemonic Numericmv2 1500 Move servo 2 to position 1500 2, 5, 220mv10 200 Move servo 10 to position 200 10, 0, 200

Translator specs

• Class (single instance for each servo)– Provides separate initialization data to exist

within each object– Separate variable data such as position and

rates are stored with each object– Functions compute output string based on

object data

- Normalized control

Class local Variable

'local variable(s) to hold property value(s)Private mvarminRange As Integer 'local copyPrivate mvarmaxRange As Integer 'local copyPrivate mvarmultiplier As Single 'local copyPrivate mvarmark As Integer 'local copyPrivate mvarservo As Integer 'local copyPrivate mvarposition As Integer 'local copyPrivate mvarreverse As Boolean 'local copyPublic outputstring As StringPublic value As IntegerPrivate mvargood As Boolean 'local copy

Why private?

• Private can help guarantee values are within appropriate ranges. This helps make sure the system doesn’t get bad information.

• Provides protection to data from outside.

• It just means a function is must be called to write data.

ASC16 Information:Command Set Example

ac (81-96 DEC) (51-60 HEX)

Acceleration

Format: ac$ accel ac$ = 81-96 for servo 1 (ac1) to 16 (ac16)

accel = 1-255

Example:

mnemonic Numeric

tl 2 ‘ set trigger level to suspend processing 119, 2

ac1 5 ‘set acceleration rate for servo 1 to 5cnts/20mS2 81, 0, 5

Accel command for servo object

Public Function Accel(ByVal rate As Integer) As StringDim locservo

locservo = mvarservo + 80Accel = Chr$(locserver) & Chr$(rate)

End Function

ASC16 Information:Command Set Example

mv (1-16 DEC) (01-0F HEX) Move servo absoluteFormat: mv$ position mv$ = 1-16 for servo 1(mv1) to 16

(mv16)position = 0-4000Description: Moves a servo to a new absolute position at

the speed and acceleration rate set for the specified servo.

Example:Mnemonic Numericmv2 1500 Move servo 2 to position 1500 2, 5, 220mv10 200 Move servo 10 to position 200 10, 0, 200

Servo Movement as seen by PC

• Movement are absolute otherwise:– Increased chance of leaving initialized range– Must poll often to stay up to date, therefore

increasing communication

Move commandPublic Function Move(ByVal pos As Integer) As StringDim bigmove As IntegerDim litmove As IntegerDim overall As Integer

If pos >= 0 And pos <= 255 Then

If mvargood Then If mvarreverse Then

overall = mvarminRange - (pos * mvarmultiplier) litmove = (overall Mod 256)

bigmove = ((overall - litmove) / 256)

Else overall = mvarminRange + (pos * mvarmultiplier) litmove = overall Mod 256 bigmove = ((overall - (litmove)) / 256) End If mvarposition = pos

Move = Chr$(mvarservo) & Chr$(bigmove) & Chr$(litmove)End If

End If

End Function

Initialization functionPublic Sub makenew()'this is surely ugly as but since cannot use new like .NET'this will do. If (mvarservo >= 1) And (mvarservo <= 16) And (mvarmaxRange <= 4000) And (mvarminRange <=

4000) And _ (mvarmaxRange >= 0) And (mvarminRange >= 0) Then mvargood = True If mvarmaxRange > mvarminRange Then mvarreverse = False mvarmultiplier = (mvarmaxRange - mvarminRange) / 256 Else mvarreverse = True mvarmultiplier = (mvarminRange - mvarmaxRange) / 256 End If End If mvarposition = 127End Sub

Using objects

• Create instantiate an object for each servo device

Dim eyeLr As New asc16stringbuilder

Dim eyeDu As New asc16stringbuilder

Dim neckLR As New asc16stringbuilder

Dim neckDU As New asc16stringbuilder

Dim mouth As New asc16stringbuilder

• Initialize eyeLr.servo = 1

eyeLr.minRange = 1390

eyeLr.maxRange = 2810

eyeLr.makenew

• UseMSComm.Output = eyeLr.Move(value) ’value range 0 255

A trivial use example

• Random eye movementPublic Sub LRAnimEye()

Dim randomx As Integer

randomx = Int(10 * Rnd) - 5

randomx = randomx * 15

MSComm.Output = eyeLr.Move(randomx + 127)

End Sub

Questions Discussion

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