Peter I. Corke - Pumaservo - The Unimation Puma servo system.rar (779752), страница 2
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Chapter 3 describes the electromechanical axis dynamics, including friction, inertia,current loop, velocity loop and position loop. The appendices provide additional informationon topics such as robot parameters, joint communications, and encoder calibration.1.1 NomenclatureElectrical signals prexed by a slash `/' are active low; the notation used on Unimation schematics is an `L' sux to the signal. ICs on circuit board are prexed by an upper-case `U' followedby a letter and a digit which designate the coordinate of the IC on the board.
Circuit diagramsfor these two servo boards may be found in the Unimate Technical Manual [20]. The mostcommonly used symbols and their units are listed in Table 1.1. The following conventions havealso been adopted: Time domain variables are in lower case, frequency domain in upper case. Transfer functions will frequently be written using the notations122K (a)[; !n] = K a + 1 !2 s + ! s + 1nn7SymbolDescriptionva vectorvxa component of a vectorAa matrixx^an estimate of xxddemanded value of xATtranspose of ABviscous frictionfforceGgear ratioGgear ratio matrixicurrentpj1Jscalar inertiaJinertia tensor, 3 3 matrixk; KconstantKiamplier gain (transconductance)Kmmotor torque constantLinductanceqgeneralized joint coordinatesQgeneralized joint torque/forceRresistanceanglevector of angles, generally robot joint anglessLaplace transform operatorSirst moment of link i. S i = mi sittimeTsample intervaltorqueCCoulomb friction torquevvoltage!frequencyzz-transform operatorUnitNms=radNAkgmskgms22A/VNm/AHradradkgmssNmNmVrad=sTable 1.1: Frequently used symbolsA free integrator is an exception, and it should be taken that (0) = s.
When specifying motor motion, inertia and friction parameters it is important that aconsistent reference is used, usually either the motor or the load, denoted by the subscriptsm or l respectively.For numeric quantities the units radm and radl are used to indicate the reference frame.8Chapter 2Digital control architecture2.1 The Arm Interface Board (AIB)The AIB is the interface between the host computer and the digital servo boards.
It allows thehost computer to send commands and read the status of individual digital servo boards via asimple parallel data interface. The signals to the host, shown in Figure 2.1, are:Data in:16-bit command or data words to the servo systemData out:CSR0:16-bit data words from the servo systemcontrols whether the data input should be interpreted as command or dataCSR0=(0 command1 dataREQA: the rising edge signies that the digital servo board has completed the last command.REQB:when true indicates that one or more digital servo boards are requesting `attention'.The servo attention word can be read to determine which axis has requested attention.NDR (New data ready): a strobe pulse (approximately 1 s wide) from the host indicatingthat new data is available on the data in lines.
In command mode (CSR0 = 0), thiscauses the command word to be latched and the appropriate servo select line (SEL bus)driven low. In data mode (CSR0 = 1) latches it causes XFER REQ to be asserted to thedigital servos.(Data transferred): a strobe pulse (approximately 1 s wide) from the host indicating that it has completed reading the data on the data out lines.DTRANSNote that the strobe pulses should be around 1 s long. If the strobe is still high when thedigital servo board responds, REQA will not rise. Example communications code is given inAppendix C.2.1.1 CommandsA digital servo command is an 8-bit value, written to the AIB, with CSR0 = 0, as shown inFigure 2.2. The low order three bits of the command word are decoded and used to address aparticular joint via the SEL bus. The next four bits specify the command to be executed by thedigital servo board. Commands may:9168Data in16Servo data6Data outArmInterfaceBoardCSR0 (cmd/data)SELCMD46REQA (ready)REQB (error)INTTOL/ATTNXFER_REQ6NDR(New data ready)DTRANS(Data transferred)/HIBYTE/DATASTBto HOST computer viaribbon cablesto digital servo boards via thePuma backplaneFigure 2.1: Signals to and from the arm interface board.Vectservo commandjoint addresscmd7 cmd6 cmd5 cmd4 cmd376543J2J1J021000011011 − AIB reads from digital servoFigure 2.2: Host command word format, written with CSR0 = 0.
write data to the servo, but the command is not executed until a data word is given (NDRstrobe); read data from the servo where the command is executed immediately and the result iswritten by the digital servo board to the AIB upon completion and from where it is readby the host.If the high order bit of the command is set the interface operates in `vector' mode and thejoints are accessed sequentially. This is useful when the same operation, read or write, needs tobe performed for all joints. The command word need be written only once prior to the sequenceof data transfer operations.
When a vector mode command is received the joint address islatched in counter U6B and incremented after each command completion, thus addressing thedigital servo boards in sequence. Figures 2.4 and 2.5 show the details.The direction of data transfer between the AIB and the digital servo board is implicit in thecommand. If bits 5 and 6 are both equal to 1 the AIB reads from the servo board, otherwisethe command is a write.10CSR00 (CMD)1 (DATA)1 (DATA)SELECT7ReadWrite0Tolerance and attention bits1 Digital servo command word0Digital servo data wordDigital servo data word1WX + status2OX + hand status3Note 1.
The eight tolerance bits appear in the low byte of the input word, and the joint attentionbits in the high byte. A joint attention bit (active low) is reset by a digital control boardwhen it encounters an error, or a zero index. Generally the joint status of the signalingaxis should be read to determine the exact problem.Note 2. When reading WX the data word is:Bit Purpose0-7 WX external input lines8 Arm power o9 STOP (same as teach box OFF)10 RUN (from the front panel switch)11 RESTART (from the front panel switch)Note 3.
When writing OX, the data word is:Bit Purpose0-7 OX external output lines8 High power enable which allows arm power to be enabled with the front panel button9 Hand open10 Hand closeIf neither hand open or hand closed are asserted the hand is in a `relaxed' state.Table 2.1: Details of SELECT7 mode operation.2.1.2 SELECT7 mode operationIf the command word's joint address is 7 the AIB operates in SELECT7 mode and the hostcommunicates with the AIB, not a digital servo board. Reading data in SELECT7 mode doesnot require waiting for REQA to become true.
This mode gives access to plant input (WX)and output (OX) signals, front panel switches, joint tolerance and attention lines. The variousoperating modes are given in Table 2.1.2.1.3 Major data pathsThe major data paths are shown in Figure 2.3. The command byte is latched by U6D and thelow order three bits are decoded to drive the servo select lines. Data direction over the digitalservo bus is implicit in the command type: commands that read from the digital servo have bits6 and 7 of the command word set. This is used by U2B to control the direction of the servobus transceivers.The axis processors read and write 16-bit host data via the 8-bit servo data bus.
Datawritten by the host is latched by U4D/U5D which the axis processor can read via the servodata bus. The active axis processor controls which byte is placed by the AIB onto the servobus by means of /HIBYTE. A command that reads data from the axis processor must wait untilthe axis processor has written data into the 16-bit register (U4D, U5D) on the AIB. The axisprocessor places 8-bits of data at a time onto the servo bus, and uses /HIBYTE to select whichhalf of the AIB register will be written, and /DATASTB to latch it.11WX/STOP/OFF/RESTART16U3D,U2E,U1F1616Data in1616U4F,U4E,U3E,U2F8INTTOL/ATTN8datalatchU5D,U4D8A/D8816Servo dataData outU4C,U5C4cmdlatchU2D3jointcountU6DCMD6DecodeSELFigure 2.3: Major data paths in the AIB.The READADC command is a special case since no data is read from the digital servoboard.
Instead the output of the ADC on the AIB is gated onto the output data bus. TheREADADC command is processed by the digital servo boards, but they simply acknowledge thecommand after a programmed delay, to cover the conversion time of the ADC (around 100 s)and provide the REQA acknowledgment.2.1.4 The digital servo backplaneThe Puma backplane, shown in Figure 2.1, carries a number of signal busses between the digitalservo cards and the arm interface board.
Some busses are common to all boards (such as servodata), while others have one signal connected to each board, via the custom backplane (suchas SEL). The busses include: CONTROL bus. This bus contains the data coordinating signals:{ /HIBYTE used by the servo board to select which byte the AIB places on the servodata bus;{ /DATASTB data strobe, used by the servo board to latch data into the AIB;{ /XFER REQ strobe indicating valid command on CMD bus, and causes an NMI to theselected axis processor;{ HALT halt operation of the axis processor;Data transfer direction is implicit in the current command. /XFER ACK is asserted by thejoint servo when it has completed a command, and toggles the state of the AIB's REQAline to signal the host. In `vector' mode, it is also used to increment the joint counter onthe arm interface card (U6D) via the /CTUP signal.
SEL bus. Each board is selected by one of six joint select lines in the SEL bus. These linesare driven by a demultiplexer, U6E, on the arm interface card from the lower 3-bits (joint12Command writtenHost readsdata fromjoint 0CSR0Host readsdata fromjoint 1NDRDTRANSWJCRLcommand latchedSELjoint 0joint 1joint 2CMD/XFER_REQjoint 0interruptedNMIjoint 1interruptedjoint 2interruptedservo data2 bytes of datawritten by digital servo/XFER_ACKREQA/CTUPfor vector mode onlyjoint addresscounter incrementedFigure 2.4: Timing details for vector mode reading.number eld) of the servo command word.
When the card is selected and /XFER REQ isasserted the axis processor is interrupted. CMD bus. This bus is provided in parallel to all servo cards and is acted upon only by theselected card. The command consists of bits 4 to 7 of the servo command word. Servo data bus. This bidirectional 8-bit bus is used to transfer 16-bits of data betweenthe joint servo cards and the arm interface card. For servo card writes, signal /HIBYTEindicates which byte the arm interface must latch and /DATASTB latches the data. Forreading, /HIBYTE selects which byte the arm interface must multiplex onto the data bus. INTTOL bus.
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