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7.4

Strain Gages

Due to variations in materials, manufacturing and external forces, the strain gage values may
change.  These changes will affect the zero force reading for each beam differently.  To maintain
consistent results, the zero force reading needs to remain constant.  Each strain gage is equipped
with a balancing potentiometer.  Adjusting the balancing potentiometer will change the strain gage
output for that finger.  Adjust the BH8-262 balancing potentiometer until the no-load value is
between 100 and 140.  Use the following steps to zero the strain gages:

1.

Initialize the BarrettHand™.

2.

Terminate the spread motor so it can be moved around the palm.  (Issue the "T" command)

3.

Remove the Shroud Cover screws shown in Figure 23.  Some models of the BarrettHand™
will have four Shroud Cover screws.  Remove the Shroud from the finger link.

Figure 23 - Shroud Removal

4.

BH8-262 users should run the program 

Monitor Strain

.  This program will continuously

sample the strain gage values and print them to the screen.  Another option is to run the
BarrettHand Control GUI and poll for strain values.

5.

Adjust the balancing potentiometer using a small flat head screwdriver until the desired value
is reached.  The balancing potentiometer requires very small adjustments, due to its
sensitivity.  Apply as little pressure as possible on the balancing potentiometer during
adjustment.  See Figure 24.

Page 56 of 89

 

Shroud Cover 
Screws 

Shroud Cover 

Summary of Contents for BarrettHand BH8-262

Page 1: ...BarrettHand BH8 Series User Manual Firmware Version 4 4 x Updated on October 27 2010 ...

Page 2: ...G METHOD 1 LAB BENCH STAND 17 3 2 MOUNTING METHOD 2 ON ROBOT ARM 17 3 2 1 Robot Arm Adapter 17 3 2 2 Installing the Hand Cable on a Robot Arm 18 3 3 ELECTRICAL CONNECTIONS 19 3 4 HOST COMPUTER 20 3 5 INSTALLING BH8 SERIES CONTROL SOFTWARE 20 3 6 POWER UP SEQUENCE 20 3 7 UPLOAD FIRMWARE 21 4 CONTROL MODES SUPERVISORY AND REALTIME 22 5 SUPERVISORY CONTROL MODE 23 5 1 OVERVIEW 23 5 1 1 Commands 23 5 ...

Page 3: ...BLE PRETENSION 48 7 2 FASTENER CHECK 50 7 3 LUBRICATION 51 7 3 1 Finger Replacement 52 7 4 STRAIN GAGES 57 8 TROUBLESHOOTING 59 9 THEORY OF OPERATION 65 9 1 ELECTRONIC ARCHITECTURES 65 9 2 LOW LEVEL MOTOR CONTROL 66 9 2 1 Trapezoidal Control 67 9 2 2 Velocity Control 67 9 3 MECHANISMS 67 9 3 1 TorqueSwitch 67 9 3 2 Spread Motion 71 9 4 OPTIONAL STRAIN GAGE JOINT TORQUE SENSOR 72 9 5 FORWARD KINEMA...

Page 4: ...IGURE 12 PRETENSIONING THE TENDON CABLE 48 FIGURE 13 IMPORTANT FASTENER LOCATIONS 49 FIGURE 14 LUBRICANT APPLICATION POINTS 51 FIGURE 15 PREPARE BARRETTHAND 52 FIGURE 16 LOCATE SHOULDER SCREW 52 FIGURE 17 GENTLY LIFT AND ROTATE FINGER OFF 53 FIGURE 18 SLOWLY PULL FINGER AWAY FROM MOTOR BODY 53 FIGURE 19 ADJUST ANGLE OF 2ND LINK 53 FIGURE 20 CHECK ADJUST THE FINGER ANGLE 54 FIGURE 21 CLOSE UP OF EL...

Page 5: ...ITY MEASURED BEFORE BREAKAWAY 70 FIGURE 33 PINCH GRASP TORQUE 71 FIGURE 34 STRAIN GAGE JOINT TORQUE SENSOR 72 FIGURE 35 STRAIN GAGE TORQUE CURVES 73 FIGURE 36 BARRETTHAND IN ZERO POSITION 74 FIGURE 37 D H FRAME ASSIGNMENT FOR GENERALIZED FINGER 75 FIGURE 38 FINGER JOINT MOTION LIMIT RANGE 78 FIGURE 39 SPREAD JOINT MOTION LIMIT RANGE 79 FIGURE 40 BARRETTHAND DIMENSIONS 81 FIGURE 41 TORQUESWITCH ACT...

Page 6: ... TABLE 7 BARRETTHAND MOTOR PROPERTIES 65 TABLE 8 D H PARAMETER VALUES FOR ALL FINGERS 74 TABLE 9 D H LINK PARAMETERS FOR FINGERS 75 TABLE 10 FINGER AND SPREAD JOINT RATIOS 77 List of Equations EQUATION 1 HOMOGENEOUS TRANSFORM BETWEEN FRAME I 1 AND I 73 EQUATION 2 FORWARD KINEMATICS FROM WRIST FRAME TO FINGERTIP 74 EQUATION 3 FORWARD KINEMATICS MATRIX FOR FINGER F1 76 EQUATION 4 JOINT 3 POSITIONS B...

Page 7: ...and low weight of the BarrettHand assures that the enhanced dexterity does not compromise arm payload Its low mass and short base to grasp center distance minimize joint loading on the host robot and reduce extraneous arm movements during object reorientation The custom control electronics package is contained entirely within the palm shell reducing electrical wiring to a single cable carrying all...

Page 8: ...a single DC brushless servo motor The joints of each finger are coupled through Barrett s patented TorqueSwitch which automatically switches motor torque to the appropriate finger joint when closing on a target object Using the fingers together allows the BarrettHand to grasp a wide variety of objects securely The TorqueSwitch combined with the spread function makes object grasping nearly target i...

Page 9: ...1 1 4 Power Supply Figure 2 BarrettHand BH8 28x 48 Volt Universal Power Supply Page 9 of 89 ...

Page 10: ...er via the serial cable and the control electronics in the BarrettHand palm shell via the Hand cable This Power Supply switches automatically to local voltage standards 95 130 190 260 VAC at 50 60Hz around the globe and contains built in surge protection 1 1 5 Electrical Cables All necessary electrical cables are included in the basic BH8 SERIES System The required electrical connections to the di...

Page 11: ...Figure 4 Earlier BarrettHand BH8 SERIES 24 Volt Power Supply Figure 5 Cable Connections to the Earlier BH8 SERIES Power Supply Page 11 of 89 ...

Page 12: ...rol GUI is a cross platform compatible Windows Linux application that allows control of the BarrettHand quickly and easily The BarrettHand Control GUI can be used to demonstrate functionality test Supervisory and RealTime control sequences and how to save those sequences as ASCII text or even as cross platform compatible C code along with a Makefile literally with the click of a Generate C Code bu...

Page 13: ... The BarrettHand has firmware that resides on the control electronics inside the palm The firmware is a compiler generated text file that may be uploaded to the hand through the boot loader and the configuration tab in the GUI The firmware receives commands controls the motors sets and retrieves properties and reads or writes to the EEPROM See Sections 4 through 6 for more information on firmware ...

Page 14: ...orque externally applied about the distal joint over a range of 1 N m 2 kg at finger tip is about 20 N 5 cm 1 N m This option uses strain gages to measures the differential tension in the tendon running through each finger to the second joint The information is processed in additional on board circuitry when this option is installed it is accessed by requesting the present strain gage property The...

Page 15: ...evels Do not allow the BarrettHand to be exposed to liquids that may cause electrical short circuit and put you at the risk of electrical shock Keep dirt away from the exposed gear and cable drives located at the joints Do not exceed the load limit of the fingers 2 kg per finger Consider all loading situations including accelerated loads cantilever loads from long objects robot collisions active l...

Page 16: ...to roughly 120 degrees and rest the unit on its fingertips Place the stand feet up onto the hand Note the alignment of the BarrettHand relative to the wire strain relief clips to ease connection of the BarrettHand Cable Make sure the Power Supply is turned OFF and then route the BarrettHand Cable through all three cable clips on the lab bench stand and plug it into the BarrettHand Tighten the cabl...

Page 17: ...and has been designed for compatibility with both internal and external mounting schemes When a robot arm does provide an internal channel the cross section of the channel is tightly constrained Therefore the Hand cable has been made with a particularly tiny connector at one end to ease internal installation The base of the Hand Adaptor includes an opening to accommodate direct access from an inte...

Page 18: ...er Supply Line Cord into any convenient outlet and verify that it is switched OFF Attach the one end of the Hand Cable to the Power Supply and the other end into the Hand Tighten the strain relief screws using the Phillips screwdriver provided in the toolkit CAUTION Be sure you are not supplying 48 V to a 24 V hand Check the switches on the bottom of a BH8 280 hand under the access panel Make sure...

Page 19: ... functionality help you learn how to independently write C code and automatically generate C code based on tested algorithms1 Run the bhand exe installer on Windows or bhand deb on Ubuntu to install all necessary files that are included on a flash drive or obtained online for using the BarrettHand Control GUI the most recent version of firmware online manuals and example programs 3 6 Power Up Sequ...

Page 20: ...r to ensure proper operation The download process takes only a few minutes as follows 1 Verify the BarrettHand is plugged into the Power Supply 2 Verify the host computer is plugged into the Power Supply 3 Verify the Power Supply is attached to a power source 4 Run the BarrettHand Control GUI from Windows or Ubuntu 5 Select the Hand model number and either CAN or Serial depending on your connectio...

Page 21: ...e found on the 262 hand are also available on the 280 hand BH8 280 Supervisory commands are handled separately by each Puck that communicates on the same CAN bus in the Hand It is recommended to use the BarrettHand API for handling the underlying low level CAN communication methods The 280 hand is property based and CAN messages are sent to set Hand properties and Get messages may be sent to reque...

Page 22: ...opriately with any error message followed by a prompt for the next command 5 1 1 Commands When the BarrettHand firmware is ready to process a command it prints a prompt of to the host computer A command can then be entered as a single line terminated by a carriage return character 0x0d Once the firmware receives the carriage return it processes the line executes the command prints any error result...

Page 23: ...mand can t have motor prefix 8192 Overtemperature fault tripped 16384 Cntl C abort command received 5 2 Command List Supervisory mode commands are organized into the following five 5 categories Movement Motor properties Global properties Administrative Advanced 5 2 1 Movement Commands Movement commands are motor commands they immediately affect one or more of the motors Each can take motor prefixe...

Page 24: ...n number of counts If no argument then the amount to open is specified by value s the DS property Arguments Distance to move 0 to 20000 optional Example 12IO 5000 Notes Command IC Name Incremental Close Purpose Closes the selected motor s the given number of counts If no argument then the amount to close is specified by the value s DS property Arguments Distance to move 0 to 20000 optional Example...

Page 25: ... initialized it will still turn the selected and initialized motor s s power off Command TC Name Torque Controlled Close Purpose Commands velocity of selected motor s in the direction that closes the finger s with control of motor torque at stall Arguments none Example STC Notes Command TO Name Torque Controlled Open Purpose Commands velocity of selected motor s in the direction that opens the fin...

Page 26: ...e firmware is lost However this command should not be performed more than 5 000 times or the hand electronics may need repair Command FDEF Name Finger Default Purpose Sets the selected motor s s properties back to their factory default values Arguments none Example SFDEF Notes Does not save the changed values to non volatile storage Command FLIST Name Finger List Purpose Lists all of the standard ...

Page 27: ...itor so it retains its value even if the firmware is lost Command PSAVE Name Property Save Purpose Saves the global properties to non volatile storage Arguments none Example PSAVE Notes The non volatile storage used does not depend on the super capacitor so it retains its value even if the firmware is lost However this command should not be performed more than 5 000 times or the Hand electronics m...

Page 28: ... must be no space between and any command name Command RESET Name Reset Purpose Resets the hand software Equivalent to doing a power cycle Arguments none Example RESET Notes Command ERR Name Error Purpose If given an argument lists the errors represented by that argument If not given an argument lists all possible error values and descriptions Arguments errorNum Example ERR 3 Notes Command VERS Na...

Page 29: ...dard and advanced motor property values for the selected motor s Each property has its value s printed on one line with one value for each selected motor separated by spaces Arguments none Example 3FLISTAV Notes Can take a motor prefix Command PLISTA Name Property List All Purpose Lists all of the standard and advanced global property names Arguments none Example PLISTA Notes Command PLISTAV Name ...

Page 30: ...perty DS Name Default Step Purpose Size of IC or IO command movement if no argument specified Values 0 to 65 535 Default Finger 1700 Spread 315 Notes While DS can be set as high as 65 535 its true range of useful values is bounded by the joint limits of the axes e g approximately 0 to 18 000 for fingers and approximately 0 to 3150 for spread Property HSG Name Highest Strain Gauge Value Purpose In ...

Page 31: ...es the strain gage checking during motion commands 5 3 2 Status Motor status properties are read only and give useful motor information and feedback Property BD Name Breakaway Detected Flag Purpose To determine if breakaway has occurred Values 0 or 1 Default N A Notes Flag is set when a breakaway is detected Flag is cleared after an O TO or HI command Property BP Name Breakaway Position Purpose St...

Page 32: ...lue for the motor Values 0 to 255 Default N A Notes Returns 255 if there is no strain gauge 5 3 3 RealTime RealTime properties affect exchange of control and feedback data for motors in RealTime mode See Section 6 for more information on RealTime mode Property LCV Name Loop Control Velocity Purpose If non zero then a velocity byte will be sent in the control block for the motor Values 0 1 Default ...

Page 33: ...Purpose If non zero then the firmware sends two unsigned bytes giving the most recently recorded breakaway position for the motor Values 0 1 Default 0 Notes Property LFV Name Loop Feedback Velocity Purpose If non zero then the firmware sends a signed byte giving the present velocity for the motor divided by the LFVC property Values 0 1 Default 1 Notes Property LFVC Name Loop Feedback Velocity Coef...

Page 34: ...ingle signed byte and then sent to the host The value sent to the host should be multiplied by LFDPC and then added to the last reported position 5 3 4 Advanced Users do not generally need these properties and should avoid using them They are not listed by the FLIST or FLISTV commands they are only listed by the FLISTA and FLISTAV commands Property ACCEL Name Acceleration Purpose Maximum accelerat...

Page 35: ...Default 0 Notes FIP sets A in the HCTL 1100 controller which is applied as specified in Equation 1 on page 23 of http www hctl 1100 com HCTL 20docs HCTL 1100 20Data 20Sheet pdf Setting this property to a non zero value can drive the system unstable Property FPG Name Filter Proportional Gain Purpose Used to calculate the desired motor torque Values 0 to 255 Default 10 Notes FPG sets K in the HCTL 1...

Page 36: ...Name Initialization Velocity Purpose This value replaces MOV Motor Open Velocity during initialization this allows a consistent initialization velocity even if MOV is adjusted Values 16 to 4080 Default Finger 300 Spread 150 Notes Barrett Technology does not recommend increasing IVEL beyond its default value Permanent deformation of Bellville washers could result This would prevent the finger break...

Page 37: ...void using SGFLIP since it may be dropped in future revisions of the firmware Property TSTOP Name Time to Stop Purpose Time in milliseconds before motor is considered stopped Values 0 to 65 535 Default 30 Notes WARNING Please use caution when adjusting this property Setting TSTOP higher than its default can result in the motors heating up very quickly under moderate to heavy usage 5 4 Global Prope...

Page 38: ... downloads Property UPSECS Name Uptime Seconds Purpose The total power up time for this hand Values 0 to 4 billion Default N A Notes This value is never reset it is maintained through power failures and firmware downloads This property can accommodate 136 years of power up time before rolling over Property SN Name Serial Number Purpose The serial number of the hand Values N A Default N A Notes Thi...

Page 39: ...s returned corresponding to Couldn t reach position From the PC side of the interface Case 2 can be distinguished by reading the value of the strain gage SG and seeing if it is larger than the specified MSG Case 3 Specified goal position is achieved within MPE As soon as the goal position is reached a termination condition occurs for that motor If HOLD is false the motor is then turned off if HOLD...

Page 40: ...ol Language GCL character strings containing commands and returns a response to commands in a user supplied receive buffer The string is parsed into commands that may contain a motor string prefix and possibly some parameters This allows significant backwards compatibility and allows sending commands in the form of strings and receiving responses from the hand in the form of a string A list of the...

Page 41: ...nd strain values Presently velocity feedback is calculated on the host PC automatically when the LFV is set When the listed control and feedback flags are set the RTStart method is called to begin RealTime mode RTStart accepts a second parameter to determine the desired levels of motor protection A positive value for the TSTOP property in units of milliseconds will terminate motors after TSTOP mil...

Page 42: ...ncluded then it is sent for each motor selected for the LOOP command in motor number order followed by any global datum For each motor any of a set of data can be included Whether or not a specific piece of data should be included is controlled by one of ten flag properties LCV LCPG LCT LFAIN LFBP LFV LFS LFAP LFDP and LFT If a given property is true then its corresponding datum is included in the...

Page 43: ...Feedback Strain Unsigned 1 byte LFAP Loop Feedback Absolute Position Unsigned 2 bytes LFDP Loop Feedback Delta Position Signed 1 byte LFBP Loop Feedback Breakaway Position Unsigned 2 bytes LFAIN Loop Feedback Analog Input Unsigned 1 byte In addition to the motor feedback data there is a single global feedback datum which is sent if its corresponding global property is non zero LFT Loop Feedback Te...

Page 44: ... to 1754 The next feedback block will include the delta position 123 which actually means 246 the reported position will be updated to 2000 Subsequent feedback blocks will include the delta position value 0 until the next position change If desired any unreported position change can be discarded by setting the LFDPD Loop Feedback Delta Position Discarded global property to true With this set the a...

Page 45: ...cient 1 to 255 Actual velocity is divided by LFVC to get LFV N A LFS Loop Feedback Strain Flag If True RealTime feedback block will contain strain information 1 unsigned byte LFAP Loop Feedback Absolute Position Flag If True RealTime feedback block will contain absolute position 2 unsigned bytes LFDP Loop Feedback Delta Position Flag If True RealTime feedback block will contain delta position 1 si...

Page 46: ... for motor 1 1 signed byte of velocity for motor 2 Each feedback block will consist of seven bytes 1 unsigned byte of strain for motor 1 1 signed byte of delta position for motor 1 1 unsigned byte of strain for motor 2 1 signed byte of delta position for motor 2 1 signed byte of delta position for motor 4 1 unsigned byte of temperature Each control block from the host will stimulate a feedback blo...

Page 47: ...easure the tensions differentially reduces the effect of actual pretension in the cable as long as the cable is not actually loose Under normal circumstances the cables remain pretensioned indefinitely But under heavy use over thousands of cycles it can begin to relieve its pretension You can easily readjust the pretension through Barrett Technology s patented cable tensioning mechanism as follows...

Page 48: ... TENDON The pretensioning mechanism is stronger than the tendon and is capable of snapping it if over tightened Excessive pretension will change the frictional properties in the finger drives and may reduce the finger s range of motion 3 Retighten the hex set screw until it is snug against the tensioner screw NOTE It is advisable to completely remove the hex set screw to apply Loctite 222 to its t...

Page 49: ...t Ideally this inspection should occur monthly under heavy use conditions Should any fasteners have become dislodged during operation contact Barrett Technology for replacements or replacement specifications Do not replace fasteners without contacting Barrett Technology as many fasteners have strict length specifications Torsion Pins Base Screws Retainer Screws Hand Cable Socket Worm Retainer Plat...

Page 50: ...ding to Figure 14 and the schedule in Table 6 NOTE for BH8 262 hands Issuing the following command to the hand will return the number of encoder counts divided by 1000 on each motor fget od The number of joint cycles can be determined using the following conversions Fingers 1 2 3 encoder counts 17 500 Spread encoder counts 3 100 Table 6 Lubrication Schedule Application Point Maintenance Cycle Fing...

Page 51: ... each finger from the palm assembly to access this application point See the section below on how to detach lubricate and reattach the finger 7 3 1 Finger Replacement Read all steps below before conducting this maintenance Pogo pins that connect to sensors in the hand may shear unless the finger is detached and reattached with care It is best to lubricate only one finger at a time Step 1 Turn off ...

Page 52: ...in the right hand hole shown See Figure 15 Figure 15 Prepare BarrettHand Step 3 Locate shoulder screw that connects the finger to the hand See Figure 16 Figure 16 Locate shoulder screw Step 4 Using a 2 mm hex wrench unscrew the shoulder screw Turn the hand sideways and slap the base of the BarrettHand with your palm to get the shoulder screw to fall out Page 52 of 89 ...

Page 53: ...ngaging the teeth Do not twist or rock the finger when removing or attaching it Step 6 Slowly pull finger away from the motor body Figure 18 Slowly pull finger away from motor body Step 7 Take the replacement finger and verify that the inner link is driven into its stop Using a 2 mm hex wrench insert it into the right hand hole and rotate counter clockwise until the finger stops moving See Figure ...

Page 54: ...as been removed the fingertip position must be reset Use a 2 mm hex wrench to manually rotate the Joint 3 drive 5 1 2 revolutions from the position where both links are inline and horizontal Figure 20 Check adjust the finger angle Step 9 If necessary add Mobil 1 Synthetic grease to the motor body cavity using the syringe provided Cover all gear teeth with a thick bead of grease Reverse Steps 5 and...

Page 55: ...re 22 Figure 22 Apply downwards pressure and secure shoulder screw Step 11 Verify that the finger operates smoothly Using a 2mm hex wrench in the right hand hole see Figure Error Reference source not found drive the finger manually through its range of motion Finger replacement is complete Page 55 of 89 ...

Page 56: ...ead motor so it can be moved around the palm Issue the T command 3 Remove the Shroud Cover screws shown in Figure 23 Some models of the BarrettHand will have four Shroud Cover screws Remove the Shroud from the finger link Figure 23 Shroud Removal 4 BH8 262 users should run the program Monitor Strain This program will continuously sample the strain gage values and print them to the screen Another o...

Page 57: ... Potentiometer 6 After balancing the strain gage exit the Monitor Strain program put the shroud and shroud cover back on and secure the screws Be careful not to touch the strain gage or damage any of the electrical wiring when replacing the shroud Page 57 of 89 ...

Page 58: ...er 2 Check that the serial cable is a straight through extension cable 3 Verify the Power Supply is turned on 4 Firmware may no longer be valid Try downloading the firmware according to Section 3 7 5 Host computer baud rate and BarrettHand baud rate may be set to different rates Close the BarrettHand Control GUI and reset the BarrettHand by cycling power on the BarrettHand Power Supply Restart the...

Page 59: ...pulley as shown in Figure 25 4 Verify idler pulley rotates freely on the shoulder screw The shoulder screw should not be tightened against the idler pulley If so loosen shoulder screw shown in Figure 25 so the idler pulley will move with cable motion 5 If the problem persists contact Barrett Technology Symptom Only the fingertip closes when the entire finger should close Premature Breakaway Possib...

Page 60: ...Technology Symptom Finger moves in opposite direction of commanded motion Possible Solution 1 Reload firmware 2 There is an encoder feedback problem Reinitializing the finger should solve the immediate problem If this recurs contact Barrett Technology for servicing Symptom The TorqueSwitch does not breakaway properly prohibiting the fingertip from completing a form grasp around an object Possible ...

Page 61: ...Figure 26 Manual Torque Switch Activation Joint 3 Drive Access Joint 2 Drive Access Figure 27 Manual TorqueSwitch Activation Drive Holes Page 61 of 89 ...

Page 62: ...n 7 3 for lubrication instructions Alternatively the commanded gains or commanded velocities from nominal allows you to compensate 3 If the problem persists contact Barrett Technology Symptom Fingers will not close completely Possible Solution 1 Adjust close target CT so that it is either at or just beyond the actual palm surface 2 Verify that the outer link has not broken away prematurely 3 Verif...

Page 63: ...ve backlash Possible Solution 1 The pretension in the cable is too low Refer to Section 7 1 to set the finger cable pretension properly If the problem persists contact Barrett Technology 2 The finger cable is broken Verify this by removing the Shroud Cover see Figure 23 and inspecting the cable The cable should be intact and not broken If the cable is broken contact Barrett Technology Symptom The ...

Page 64: ...h servo cycle BH8 262 CPU Board The CPU board handles all set up communications and high level control of the power boards including coordinated motion force monitoring and motor speed monitoring The main processor is a Motorola 68HC811E2FN microcontroller which contains 256 bytes of RAM and 2Kbytes of EEPROM The CPU board contains a 128 Kbytes RAM chip external to the microprocessor which is used...

Page 65: ...lace worn brushes after the motors have been in service over a period of time Table 7 shows BarrettHand motor properties Table 7 BarrettHand Motor Properties Number of Phases 3 Number of Poles 6 Rotor Magnets Highest Grade Samarium Cobalt Rare Earth Commutation Brushless Electronic PWM Peak Torque 5 N cm 8 oz in Motor Constant 0 83 N W cm 1 17 W in oz Position Feedback 360 counts rev incremental o...

Page 66: ... 1100 20Data 20Sheet pdf 9 2 2 Velocity Control The Velocity Control is used during torque close and torque open commands TC and TO These commands use proportional gain multiplied by the instantaneous velocity error to control the motors The motor torque responds for each motor controller according to MCn K 4 Yn K depends on the Boolean LCPG flag If LCPG is true than K is equal to the loop control...

Page 67: ... with a known motor torque thereby setting the threshold torque for disengaging the spur gear If the inner finger link while closing contacts a target object of sufficient stiffness to increase the torque in the gear train above the threshold torque the clutch will disengage from the Belleville spring washers When the clutch is disengaged the threaded spur gear free wheels on the threaded shaft al...

Page 68: ...hile the Inner Link Holds Position Clutch Near End of Travel on Threaded Shaft when Fingertip Contacts Object Figure 30 TorqueSwitch Operation The force required to cause the TorqueSwitch to disengage can be set using the properties IVEL IOFF IHIT and OT Barrett Technology recommends that users should not change IVEL IOFF and IHIT from their default values The following Breakaway force Curve can b...

Page 69: ... to an object being grasped the command TorqueClose and TorqueOpen must be used These commands use the Velocity Control Law with the properties MCV and MOV To determine the amount of desired force at the fingertip use Figure 32 to select proper velocities Page 69 of 89 ...

Page 70: ...n mid grasp creating a more stable grasp of oddly shaped target objects Should you wish to control the spread position of the fingers the complete command set available to the fingers is also available for the spread including commands for fixed increment motion and move to position commands The sustainable torque that the spread fingers can exert continuously in a pinch type grasp is shown in Fig...

Page 71: ...gages applied and wired in a Wheatstone Bridge configuration When a force is applied to the fingertip Force A the torque is measured by the amount of deflection in the beam The beam deflection is proportional to the difference in cable tension which translates to a force on the pulley attached to the flexible beam Force B The flexing in the beam creates a measurable voltage change in the Wheatston...

Page 72: ...nd the expected no load SG value should be between 1600 and 2240 If the gage values do not fall within the specified range see Section 7 4 For improved accuracy the user can measure the no load value before taking readings of SG For example issue a GO command and then a FGET SG command to open the fingers against their J2 stops J3 has no open stop so its torque will measure only second order effec...

Page 73: ... finger is considered its own manipulator and is referenced to a wrist coordinate frame in the center of the palm Use the forward kinematics calculated in this section to determine fingertip position and orientation with respect to the palm Equation 1 is used to determine the transforms between axes i and i 1 Τ 1 0 0 0 c c s s c s a 0 s c 1 1 1 i 1 i 1 1 1 i 1 i 1 i i 1 i i i i i i i i i i i i i d...

Page 74: ...l Fingers Parameter Value Notes Aw 25 mm A1 50 mm A2 70 mm A3 50 mm DW 84 mm Palm offset distance depends on model D3 9 5 mm Finger endpoint depth offset Φ2 0 to 0 4 Initialization offset in Radians IOFF Φ3 42 Joint 3 offset is actually in Radians All of the kinematics for the BarrettHand are derived from the zero position The configuration of the fingers and spread in the zero position of the Bar...

Page 75: ... 4 A3 π 2 D3 0 Where k is defined as the desired finger 1 2 3 r is either 1 1 0 for F1 F2 F3 respectively j is either 1 1 1 for F1 F2 F3 respectively The transforms from each axis to the next can be determined using the homogeneous transform in Equation 1 and finger link parameters in Table 9 Each of the first three link parameters are fixed and the fourth one is configuration dependent on one of ...

Page 76: ...er link stops moving and all the joint torque is applied to the outer link Users that have inner link joint position sensors will be able to determine finger joint positions at all times For earlier hands without inner link position sensors it may be possible to estimate joint positions after detecting breakaway This section is concerned with equations for forward kinematics and does not attempt k...

Page 77: ...he same ones used on the motor for position feedback The forward kinematics from section 9 5 that are used to calculate end tip positions depend on the configuration of joint positions for each finger joint 2 and joint 3 and the spread Calculate positions in radians for each joint including spread finger joint 2 and finger joint 3 These will be the joint positions before breakaway Joint 3 position...

Page 78: ...22 Θ32 has a maximum joint motion limit of 140 with no object blocking movement and Θ11 in the full close or open position The outer link Θ13 Θ23 Θ33 has a maximum joint motion limit of 48 when Θ11 is fully open or closed and there is no object in the grasp as shown in Figure 38 When the spread is in any position other than full open or close the fingers may not have the full range of motion due t...

Page 79: ... object blocking movement and all fingers in the full open position If the fingers are partially closed or there is an object in the grasp Θ11 may be restricted due to finger interference See Figure 39 0 0 180 180 Figure 39 Spread Joint motion limit Range Page 79 of 89 ...

Page 80: ... counts full finger open to full close Weight BarrettHand 1 18 kg 2 60 lb Optional Arm Adapter B0133 0 2 kg 0 4 lb additional Payload 2 0 kg 4 4 lb per finger at tip Motor Type Samarium Cobalt brushless DC servo motors Mechanisms Worm drives integrated with patented cable drive and TorqueSwitch Power Requirements Single phase AC electrical outlet with ground Load 500 W Phases Single Voltage 95 130...

Page 81: ...ions Available Options B029A Strain gage Fingertip Torque Sensors for all three fingers B0111 C Function Library B01C3 Subscription Service US Patents patents established and pending in other countries 5 501 498 5 388 480 4 957 320 Page 81 of 89 ...

Page 82: ...e weight bulk heat power and cost of the BarrettHand one motor drives the spread action of both fingers synchronously and symmetrically about the palm The spread motion adds surprising dexterity One design feature of the spread motion is that unlike the curling motions of each finger the spread is highly backdrivable so that the spread compliance is controllable By setting low spread compliance th...

Page 83: ...f breakaway Figure 41 plots velocity during TorqueSwitch activation which is identified by a notch in velocity While the deceleration part of the notch depends on the compliance of the object the re acceleration is independent so the algorithm measures only the re acceleration Acceleration is set with parameter BDAT 0 2 4 6 8 10 12 0 14 28 42 56 70 84 98 112 126 140 154 Time ms Velocity Cts ms Fig...

Page 84: ...o closing and opening the spread completely 6200 encoder counts for a 262 hand and 71900 encoder counts for a 280 hand Firmware Software that is embedded in a hardware device that internally controls various electronic devices Updated firmware that contains additional features and bug fixes is supplied to the end user by the Manufacturer Grasp n The state in which an object has been firmly contain...

Page 85: ...e palm This motion allows the fingers to be positioned around the palm for the best grasp Spur Gears A gear having straight parallel teeth that are perpendicular to the gear s face Supervisory Mode A control mode of the BarrettHand which allows you to issue high level commands to control motion and change properties The BarrettHand does not accept a new command until the previous command is finish...

Page 86: ...5 of puck ID 1 to STATUS_READY 2 Property to issue a command over CAN CMD 29 Commands HOME 7 HI 13 IC 14 IO 15 C 18 M 19 O 20 T 21 Example setProperty bus 0 canID 1 property 29 verify FALSE value 18 Issue a Close command over CAN Issue high level command MessageID CAN ID of the puck you want the property from Payload 4 bytes 0x80 CMD 29 0x00 command 0x00 Example DLC 4 MsgID 1 Payload 0x9D 0x00 0x1...

Page 87: ...er 64 Motion control chip 64 Motor Power boards 64 PWM 64 RAM 64 Serial communication 64 C Clutch 67 Communications 13 19 Computer 19 Control software Installation 19 System 12 Cycle 50 84 D DC brushless servo motor 8 Dimensions 81 E Electrical Connections AC Line Cord 10 18 DB 9 Extension Cable 10 Hand Cable 10 18 Power Supply 18 Electronic architectures 64 Encoder 60 65 77 80 F FAQ 82 Fastener c...

Page 88: ...31 P 32 43 S 22 32 SG 32 62 Motors Acceleration 66 Brushless 65 Feedback 65 Maximum velocity 66 Peak torque 65 Phases 65 Poles 65 Proportional gain 66 Trapezoidal Profile Control 66 Type 80 Velocity 65 80 Velocity Control 66 Velocity error 66 Mounting 8 12 14 17 Movement Commands C 23 30 31 34 HI 24 28 31 HOME 24 30 31 IC 24 30 31 66 IO 24 30 31 66 LOOP 24 42 43 M24 30 31 66 O 30 31 36 T 25 56 TC ...

Page 89: ...peration 71 Torque curves 73 Zero force 56 Subscription service 14 Super capacitor 20 Supervisory control 85 Supervisory Mode 21 22 Switches Under 280 access panel 18 Synchronous 13 System Options 14 T Threaded base 8 Threaded locking ring 14 17 85 Torque wrench 13 TorqueSwitch 8 66 82 83 85 TorqueSwitch Reset 76 Threshold torque 67 Troubleshooting 58 Close position 62 Communication 58 Finger move...

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