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Barrett BH8 Series, User Manual

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Barrett BH8 Series User Manual Download Page 80

BH8-Series – User’s Manual 

[email protected] 

www.barrett.com

 

 

© 2007 Barrett Technology®, Inc. 

Document: D3000, Version: AF.00 

Page 78 of 82 

 

Appendix C  GLOSSARY 

 
API - An acronym for Application Programming Interface, the set of commands that an 

application uses to request and carry out lower-level services performed by a computer's 
operating system  

 
Backdrivability - Backdrivability is the measure of how accurately a force or motion that is 

applied at the output end of a mechanical transmission is reproduced at the input end.  In a 
mechanical robot-like linkage, good backdrivablility means that a person can grab the enditp 
of the linkage and move it around effortlessly. 

 
BarrettHand™ – The 1.2 kilogram dexterous robotic Grasper™ as described in Section 1.1.2. 
 
BarrettHand™ System  - The entire system received from Barrett Technology, Inc.  Includes all 

components as listed in Section 1.1, plus any additional options as described in Section 1.1.2. 

 
Belleville Spring Washer - A conical washer that has geometry specifically formed to produce a 

desirable spring constant. 

 
Cycle - (Finger) The equivalent to closing and opening the finger completely once, 35000 encoder 

counts. 

 

(Spread)  The equivalent to closing and opening the spread completely, 6200 encoder counts. 

 
Firmware - Software that is embedded in a hardware device that allows reading and executing the 

software, but does not allow modification, e.g., writing or deleting data by an end user. 

 
Grasp – (n.) The state in which an object has been firmly contained and secured by the 

BarrettHand™. 

 

(v1.) The method by which the BarrettHand™ closes its fingers around an object in order to 
secure it. 

 

(v2.) The collective term for fingers one, two and three, as defined in the BarrettHand™ 
control software. 

 
Graspcenter - The center of an object being grasped by the BarrettHand™. 
 
Hysteresis - The dependence of the state of a system on its previous history. 
 
Idler Pulley - A fixed or adjustable disc support for a drive cable or belt.  It is used in the 

BarrettHand™ for strain gage beam deflection. 

 
Industrial Gripper - These grippers have one degree of motion freedom, and can only execute an 

open/close motion.  Because of the simple kinematics, the gripper fingers often must be 
specifically designed for the parts that have to be grasped.  Product changes require changes 
to the gripper assortment, increasing the product change-over time.  Furthermore, an increase 
of the number of required grippers increases the number of required gripper changes during 
assembly. 

 
Kinematics - The science of motion which treats motion without regard to the forces which cause 

it, specifically all the geometrical and time-based properties of position. 

 
Lexan® - 

Α 

water clear, high-impact resistant polycarbonate used to make the BarrettHand™ lab 

bench stand. 

 
Pretension - The process of adding additional tension to a cable during the assembly process. 
 

Summary of Contents for BH8 Series

Page 1: ...BarrettHand BH8 Series User Manual Firmware Version 4 3x Document D3000 Version AF 00 ...

Page 2: ......

Page 3: ...n gage Joint Torque Sensors 12 1 2 4 Control Software Firmware Upgrades 12 2 SAFETY AND CAUTIONS 13 3 SYSTEM SETUP 14 3 1 MOUNTING METHOD 1 LAB BENCH STAND 14 3 2 MOUNTING METHOD 2 ON ROBOT ARM 14 3 2 1 Robot Arm Adapter 14 3 2 2 Installing the Hand Cable on a Robot Arm 15 3 3 ELECTRICAL CONNECTIONS 16 3 4 HOST COMPUTER 16 3 5 INSTALLING BH8 SERIES CONTROL SOFTWARE 16 3 6 POWER UP SEQUENCE 16 3 7 ...

Page 4: ...cks 38 6 2 2 Feedback Blocks 38 6 2 3 Loop Feedback Delta Position 39 6 3 PARAMETER SUMMARY 39 6 4 EXAMPLE 41 7 MAINTENANCE 41 7 1 FINGER CABLE PRETENSION 41 7 2 FASTENER CHECK 44 7 3 LUBRICATION 45 7 4 STRAIN GAGES 49 8 TROUBLESHOOTING 51 9 THEORY OF OPERATION 58 9 1 ELECTRONIC ARCHITECTURE 58 9 2 LOW LEVEL MOTOR CONTROL 59 9 2 1 Trapezoidal Control 59 9 2 2 Velocity Control 59 9 3 MECHANISMS 60 ...

Page 5: ...MOVAL 48 FIGURE 15 REATTACHING FINGERS AFTER MAINTENANCE 49 FIGURE 16 SHROUD REMOVAL 50 FIGURE 17 BALANCING POTENTIOMETER 50 FIGURE 18 CABLE AND IDLER PULLEY 52 FIGURE 19 MANUAL TORQUE SWITCH ACTIVATION 54 FIGURE 20 MANUAL TORQUESWITCH ACTIVATION DRIVE HOLES 55 FIGURE 21 BARRETTHAND CONTROLLER BLOCK DIAGRAM 58 FIGURE 22 BARRETT S PATENTED TORQUESWITCH MECHANISM 60 FIGURE 23 TORQUESWITCH OPERATION ...

Page 6: ...ROL PARAMETERS 40 TABLE 6 LUBRICATION SCHEDULE 45 TABLE 7 BARRETTHAND MOTOR PROPERTIES 59 TABLE 8 D H PARAMETER VALUES FOR ALL FINGERS 68 TABLE 9 D H LINK PARAMETERS FOR FINGERS 69 List of Equations EQUATION 1 HOMOGENEOUS TRANSFORM BETWEEN I 1 AND I 67 EQUATION 2 FORWARD KINEMATICS FROM FINGERTIP TO WORLD 68 EQUATION 3 FORWARD KINEMATICS FOR FINGER F1 70 EQUATION 4 MOTOR TO JOINT ANGLE TRANSFORM B...

Page 7: ...he 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 communications and...

Page 8: ...pled 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 independent The BarrettHand shown in Figure 1 is equipped with a thr...

Page 9: ...t computer 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 All three cables required to operate the BH8 SERIES connect to the Power Supply 1 Line Cord supplying AC line voltage 2 Serial Cable supp...

Page 10: ... Electrical Cables All necessary electrical cables are included in the basic BH8 SERIES System shown in Figure 4 An AC Line Cord connects the Power Supply to a wall source A Serial Cable connects the Power Supply and the host computer robot controller to establish the RS 232 communication link The Hand Cable connects the Power Supply to the BarrettHand supplying communications logic power and moto...

Page 11: ...ith the software in electronic form are 1 BHControl Interface Manual and 2 BH8 SERIES User Manual this manual The BarrettHand has firmware that resides on the control electronics inside the palm The firmware requires only ASCII characters sent over a standard serial port You build the character strings to create the desired commands The firmware then interprets the commands sent and controls the m...

Page 12: ... how to save those sequences as ASCII text or even as C code literally with the click of a Generate C Code button See the BHControl Interface Manual for more information on the Windows95 98 NT 2000 based BHControl Interface GUI 1 1 8 Maintenance Kit Included in each BarrettHand package is a maintenance kit Use the maintenance kit in accordance with the instructions in Section 7 The maintenance kit...

Page 13: ...ful tool for programming the BarrettHand using the C language on IBM compatible PC s without having to manage serial communication and timing issues The library contains easy to use functions that permit the use of Supervisory and RealTime commands in software routines developed by the end user All of the functions are available when the library is linked to the program The C Function Library also...

Page 14: ...ormation is processed in additional onboard circuitry when this option is installed it is accessed by requesting the present strain gage parameter The strain gage parameter represents the amount strain on the strain gage sensors The strain gage values can be calibrated by the customer to relate strain to joint torque See Section 9 4 for more detailed information on how the sensor works 1 2 4 Contr...

Page 15: ...t first verifying control of the unit and confirming appropriate force levels 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 accele...

Page 16: ...grees 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 cable clips to hold t...

Page 17: ...igned 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 internal cable to th...

Page 18: ... Interface firmware and example programs The BHControl Interface is a graphical Windows interface that allows you to control the BarrettHand quickly and easily The BHControl Interface can be used to test Supervisory and RealTime control sequences determine communication loop rates demonstrate functionality help you learn how to independently write C code and automatically generate C code based on ...

Page 19: ...ame Description BarrettHand Firmware v4_33 S19 Version 4 33 Firmware with RealTime mode capabilities 4 Control Modes Supervisory and RealTime The BarrettHand can be used in either of two 2 modes 1 high level Supervisory mode or 2 low level RealTime mode Most users of the BarrettHand can rely exclusively on Supervisory mode since it handles virtually every function of the BarrettHand Supervisory mo...

Page 20: ... etc Users can switch between Supervisory and RealTime modes on the fly as desired allowing for mixed mode operation If you use the BHControl Interface GUI software that runs on Windows based PCs you will likely wish to experiment with the Visual control window to familiarize yourself with the BarrettHand The Visual window relies exclusively on RealTime control mode since it must follow your RealT...

Page 21: ... more of the four Hand motors By default all four motors are affected To select fewer than four motors a motor prefix must be placed before the command with no space between the prefix and the command A motor prefix consists of one or more of the following characters Table 2 Motor Prefixes Value Motor 1 Finger F1 2 Finger F2 3 Finger F3 4 Spread G Finger F1 Finger F2 Finger F3 S Spread No Motor Sp...

Page 22: ...ry mode commands are organized into the following five 5 categories Movement Motor parameter Global parameter 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 prefixes Command C Name Close Purpose Commands the selected motor s to move fingers in close direction with a velocity ramp down at tar...

Page 23: ... SGHOME Notes Command IO Name Incremental Open Purpose Opens the selected motor s the given number of counts If no argument then opens by the value of parameter DS 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 affected motor s closes by the value s of pa...

Page 24: ...hough T will return an ERR 1 if any of the selected motor s isn t 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...

Page 25: ...n 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 may need repair Command FDEF Name Finger Default Purpose Sets the selected motor s s parameters back to their factory default values Arguments none Example SFDEF Notes Does not save the changed...

Page 26: ...rs from non volatile storage This is done whenever the firmware starts up Arguments none Example PLOAD Notes The non volatile storage used does not depend on the super capacitor so it retains its value even if the firmware is lost Command PSAVE Name Parameter Save Purpose Saves the global parameters to non volatile storage Arguments none Example PSAVE Notes The non volatile storage used does not d...

Page 27: ... all of the standard commands If immediately followed by a command name then it lists the command name and its description Arguments commandName Example HI Notes There 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 t...

Page 28: ...STA Notes Command FLISTAV Name Finger List All Value Purpose Lists all of the standard and advanced motor parameter s values for the selected motor s Each parameter 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 Parameter List All Purpose Lists all of the standard and a...

Page 29: ...mately 0 to 18 000 for fingers and approximately 0 to 3150 for spread Parameter 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 t...

Page 30: ...When possible please use HSG in place of MSG A value of 255 or 256 disables the strain gage checking during motion commands 5 3 2 Status Motor status parameters are read only and give information about the state of a motor Parameter 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...

Page 31: ...on 5 1 3 Parameter SG Name Strain Gauge Purpose The present strain gage value for the motor Values 0 to 255 Default N A Notes Returns 255 if there is no strain gauge 5 3 3 RealTime RealTime parameters affect the control and feedback data for a motor while in RealTime mode See Section 6 for more information on RealTime mode Parameter LCV Name Loop Control Velocity Purpose If non zero then a velocit...

Page 32: ...signed two byte value giving the present position of the motor Values 0 1 Default 1 Notes Parameter LFDP Name Loop Feedback Delta Position Purpose If non zero then the firmware sends a signed byte giving the change in position since the last datum divided by the value of the LFDPC parameter Values 0 1 Default 1 Notes A conflict occurs when the change in position is too great to transmit in a singl...

Page 33: ...Z FIP See http literature agilent com litweb pdf 5965 5893E pdf Parameter CT Name Close Target Purpose This is the position gone to by a C Close command Values 0 to 65 535 Default Finger 17 000 Spread 3150 Notes While CT 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 s...

Page 34: ...ition constant Values 0 1 Default Finger 0 Spread 1 Notes Since the fingers are not back drivable this is generally set to 1 only for the spread motor Parameter IHIT Name Initialization hit count Purpose If non zero then while initializing the motor impacts the hard stop the given number of times Values 0 to 65 535 Default Finger 2 Spread 0 Notes Barrett recommends not setting IHIT to a value grea...

Page 35: ...proximately 0 to 3150 for spread Parameter OT Name Open Target Purpose This is the position gone to by an O Open command Values 0 to 65 535 Default 0 Notes While OT 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 17 800 for fingers and approximately 0 to 3150 for spread Parameter SAMPLE Name Sample Time Purpose Controls...

Page 36: ...BAUD Name Baud rate Purpose Controls the serial port baud rate Value is baud rate divided by 100 Values 6 12 24 48 96 192 384 Default 96 Notes Parameter LFT Name Loop Feedback Temperature Purpose If non zero then when in RealTime mode the firmware sends a signed two byte datum of temperature in each feedback block Values 0 1 Default 0 Notes Parameter OTEMP Name OverTemperature Purpose If non zero ...

Page 37: ...vanced Parameter LFDPD Name Loop Feedback Delta Position Discard Purpose If non zero then in RealTime mode any position change that cannot be sent in a delta position datum is discarded If zero then any unsent position change is accumulated for transmission in the next cycle Values 0 1 Default 0 Notes 5 5 Termination Conditions for Movement Commands There are eight commands in Supervisory mode tha...

Page 38: ...the status code is ERR16 is 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 ...

Page 39: ...he host computer sends the Supervisory mode LOOP command specifying the motors to be controlled The Hand responds with an acknowledgment character and then awaits control blocks with or without control data When a control block is received if the control block requests a feedback block then transmission of the feedback block is started Once the complete control block is received it is acted upon a...

Page 40: ...The control data should be sent in a specific order first all data for motor 1 then all for motor 2 then motor 3 and finally motor 4 Note that if a given motor was not specified in the initiating LOOP command or if a specific value isn t enabled by the corresponding finger parameter then the corresponding datum should not be transmitted If the LCV datum is included then the hand will multiply it b...

Page 41: ...edback Delta Position Coefficient parameter clipped to a single signed byte and then sent to the host The host should then multiply the received value by LFDPC and then add it to the reported position The problem with using delta position is that the reported position can change at most by 127 128 in each cycle If the motor position changes more than this in a single cycle then the reported positi...

Page 42: ... LFVC Loop Feedback Velocity Coefficient Coefficient 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 ...

Page 43: ...y for motor 1 1 signed byte of velocity for motor 2 Each feedback block will consist of eight 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 2 signed bytes of temperature Each control block from the host will stimulate a feedback blo...

Page 44: ...ng mechanism as follows 1 Loosen the hex set screw with the right angle hex wrench provided in the maintenance kit This screw is located adjacent to the termination of the joint 3 cable on each of the fingers as seen in Figure 8 Figure 8 Hex set screw 2 Apply 15 oz in of clockwise torque to the tensioner screw located on the back of each Joint 3 housing as seen in Figure 9 A 2 mm hex torque wrench...

Page 45: ...al 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 threads before retightening it against the tensioner screw This measure is especially important if the hand is under heavy use Figure 9 Pretensioning the Tend...

Page 46: ...tionary inspection to ensure all external fasteners are in place and tight 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 Tors...

Page 47: ... all exposed gear teeth at the application points according to Figure 11 and the schedule in Table 6 NOTE 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 App...

Page 48: ...ion because you must remove each finger from the palm assembly to access this application point Read all steps below before conducting this maintenance It is best to lubricate only one finger at a time 1 Open all fingers on the BarrettHand completely 2 Shutdown the Power Supply and disconnect the BarrettHand Cable from the BarrettHand 3 Locate and remove the finger attachment shoulder screw that h...

Page 49: ...s motor along a straight line perpendicular to the motor s face Do not twist or rock the finger when removing or attaching it Open a Small Gap 0 5mm Max Lift Alignment Teeth out of Slots Pull Finger Away from Motor Face Figure 13 Removing the Fingers for Maintenance 6 Make note of the relative position of the fingertip and inner finger link since removing the finger will disengage the coupling bet...

Page 50: ...fter Finger Removal 7 Using the Mobil 1 Synthetic Grease syringe supplied with your maintenance kit apply a generous amount of lubricant around the motor pinion cavity of the motor Cover all gear teeth with a thick bead of grease See Figure 11 for lubrication points 8 Reset the fingertip position see Step 6 and replace the finger onto its motor according to Figure 15 again taking great care not to...

Page 51: ...rain 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 balancing potentiometer until the no load value is between...

Page 52: ...til 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 17 Strain Gage Beam Balancing Potentiometer Figure 17 Balancing Potentiometer 6 After balancing the strain gage exit the Monitor Strain exe program put the shroud and shroud cover back on...

Page 53: ...Possible Solution 2 Verify all connections are secure to the Power Supply BarrettHand and computer 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 BHControl Interface and reset the BarrettHand by cycling power on the BarrettHand ...

Page 54: ...ions on how to adjust 3 Verify the cable is riding properly on the idler pulley as shown in Figure 18 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 18 so the idler pulley will move with cable motion 5 If the problem persists contact Barrett Technology Symptom Only the finger...

Page 55: ...etension properly 6 Set the open velocity greater than or equal to 40 and then initialize the finger 7 Reload firmware 8 If the problem persists contact Barrett Technology Symptom Finger sticks open Possible Solution 1 Verify there are no objects or other fingers blocking the finger from closing 2 The close velocity is set too low Try increasing the close velocity to greater than or equal to 40 an...

Page 56: ...een slammed open against its stop with a high velocity setting the TorqueSwitch may need to be manually activated Insert a 2 mm hex wrench into the left Drive Access hole as shown in Figure 20 Rotate counterclockwise to open the finger fully Next press very hard against the inner link to constrain it from moving while not constraining the outer link as the person s thumb is doing in Figure 19 whil...

Page 57: ...MCV MOV FPG FDZ FIP SAMPLE ACCEL 2 Unlike GO and GC commands in which each finger is position controlled to follow a predefined trapezoidal trajectory that keeps the fingers moving precisely GTO and GTC commands apply pure proportional velocity control Each finger has slightly different friction due to manufacturing tolerances resulting in different actual velocities for the same commanded velocit...

Page 58: ...n 1 Lubricate the spread motor gears as shown in Section 7 3 2 If the palm screws have been reinstalled verify all screws are tightened with the same amount of torque Excessive torque may cause spread friction 3 If the problem persists contact Barrett Technology Symptom The threaded locking ring does not fit on the threaded base of the BarrettHand Possible Solution 1 The threaded locking ring has ...

Page 59: ...n the finger is reinstalled after being removed for lubrication Verify that the finger is seated completely and square where it attaches to the palm Verify also that the finger screw is in place and is not loose Reset the fingertip angle and reseat the finger carefully and verify that it is seated completely and square Test 2 If problem persists Hand must be serviced Symptom The spread fingers F1 ...

Page 60: ...of 9600 no parity bits eight bits per character and one stop bit The BarrettHand is capable of communicating at rates up to 38 4K baud Motor Power Boards Each power board handles current control of a single DC brushless motor in the BarrettHand using a Hewlett Packard HCTL 1100 motion control chip The optical incremental encoder signals from each motor with 360 counts per motor revolution are ampl...

Page 61: ...rol of motor position such as IO IC and M uses Trapezoidal Profile control This mode drives the motor to the desired position and returns an status code ERR32 except for O and C commands if the final position error is greater than MPE The HCTL1100 applies Trapezoidal control in two steps 1 Microseconds before the motor control is executed the HCTL 1100 constructs a 3 part trajectory that forms a t...

Page 62: ...eration is similar to that of a simple screw fastener Theoretically the torque with which one tightens a uniform screw should be equal to that which is required to subsequently loosen it neglecting inertia and provided all materials deformations remain elastic This principle holds true for the TorqueSwitch mechanism The TorqueSwitch consists of a threaded shaft a pair of Belleville spring washers ...

Page 63: ...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 all...

Page 64: ... and Free wheeling Down the Threaded Shaft Fingertip Continues to Close while the Inner Link Holds Position Clutch Near End of Travel on Threaded Shaft when Fingertip Contacts Object Figure 23 TorqueSwitch Operation The force required to cause the TorqueSwitch to disengage can be set using the parameters IVEL IOFF IHIT and OT Barrett Technology recommends that users should not change IVEL IOFF and...

Page 65: ... 150 175 200 225 250 Open target encoder counts Force N Figure 24 Breakaway Force Curve To control how much force is applied to an object being grasped the command TorqueClose and TorqueOpen must be used These commands use the Velocity Control Law with the parameters MCV and MOV To determine the amount of desired force at the fingertip use Figure 25 to select proper velocities ...

Page 66: ...ers In addition the backdrivability built into this degree of freedom causes the BarrettHand s grasp shape to change in 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 positio...

Page 67: ... the outer joint on each finger see Figure 27 The Joint Torque sensor is comprised of a flexible beam with four foil strain 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 t...

Page 68: ...ory and should exhibit a no load SG value between 100 and 140 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 effects ...

Page 69: ...r the BarrettHand were determined using the Denavit Hartenberg notation described in Introduction to Robotics Mechanics and Control 2nd Edition John J Craig Each 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 pal...

Page 70: ...ion 2 Forward Kinematics from Fingertip to World Table 8 is a list of the parameters used to determine the kinematics for all of the fingers These parameters are found in the forward kinematic equation Table 8 D H Parameter Values for all Fingers Parameter Value Aw 25mm A1 50mm A2 70mm A3 50mm DW 84mm D3 9 5mm Φ2 2 46 Φ3 50 All of the kinematics for the BarrettHand are derived from the zero positi...

Page 71: ...Link Parameters for Fingers Joint Ai 1 α α α αi 1 Di θ θ θ θi 1 r Aw 0 Dw r Θk1 π 2 j 2 A1 π 2 0 Θk2 Φ2 3 A2 0 0 Θk3 Φ3 T 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 its previous axis can be determined using the homogeneous transform in Equation 1 and the link par...

Page 72: ...es in Table 8 to determine any fingers end tip position To calculate the joint angle before the TorqueSwitch has been activated based on the motor angle use Equation 4 Θ Θ Θ Θ Θ Θ Θ Θ Θ Θ Θ Θ Θ 4 3 2 1 31 21 11 33 32 23 22 13 12 0 35 2 0 0 0 0 0 0 35 2 0 0 0 0 375 1 0 0 0 125 1 0 0 0 0 375 1 0 0 0 125 1 0 0 0 0 375 1 0 0 0 125 1 M M M M Equation 4 Motor to Joint Angle Transform before TorqueSwitch...

Page 73: ...s uses a 90 line or 360 count encoder Thus the motor angle is the encoder position 9 6 Joint Motion Limits The maximum joint motion limits for the BarrettHand are calculated based on the zero position seen in Figure 29 Depending on the position of the spread joint Θ11 and the objects in the grasp the maximum joint motion limits for the finger links may vary The inner link Θ12 Θ22 Θ32 has a maximum...

Page 74: ...BH8 Series User s Manual support barrett com www barrett com 2007 Barrett Technology Inc Document D3000 Version AF 00 Page 72 of 82 140 48 0 0 Figure 31 Finger Joint motion limit Range ...

Page 75: ...2 The spread joint Θ11 has a maximum joint motion limit of 180 with no 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 not close completely due to finger interference See Figure 32 0 0 180 180 Figure 32 Spread Joint motion limit Range ...

Page 76: ...l incremental encoder Resolution 0 008 at the finger base joint 17 500 encoder 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 ...

Page 77: ... Version AF 00 Page 75 of 82 Hand Dimensions Figure 33 BarrettHand Dimensions 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 78: ...wo opposable fingers and one fixed finger To minimize the number of motors and thereby the 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 backd...

Page 79: ... 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 Figure 34 TorqueSwitch Activation Graph For more questions please contact Barrett Technology Cu...

Page 80: ...reading and executing the software but does not allow modification e g writing or deleting data by an end user Grasp n The state in which an object has been firmly contained and secured by the BarrettHand v1 The method by which the BarrettHand closes its fingers around an object in order to secure it v2 The collective term for fingers one two and three as defined in the BarrettHand control softwar...

Page 81: ...ws 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 parameters The BarrettHand does not accept a new command until the previous command is finished Threaded Locking Rin...

Page 82: ... Initialize Library 18 Start Download 18 C C Function Library 12 Clutch See TorqueSwitch Communications 12 17 59 Computer 17 Disk space 17 RAM 17 Control software 10 Installation 17 CPU board 59 Cycle 46 79 D DC brushless servo motor 7 Dimensions 76 E EEPROM 59 Electrical connections 17 AC Line Cord 8 9 17 Hand Cable 9 Serial Cable 8 9 Electronic architecture 59 Encoder 54 59 60 72 75 Error codes ...

Page 83: ...0 40 S 20 30 SG 30 57 Motors 60 75 Acceleration 60 Feedback 60 Maximum velocity 60 Peak torque 60 Phases 60 Poles 60 Proportional gain 60 Trapezoidal Profile control 60 Trapezoidal Profile control 60 Velocity 60 75 Velocity control 60 Velocity error 60 Mounting 7 9 12 15 Movement Commands C 21 28 29 32 HI 22 26 29 HOME 22 28 29 IC 22 28 29 60 IO 22 28 29 60 LOOP 22 38 39 40 M22 28 29 60 O 28 29 34...

Page 84: ...e 13 42 50 66 Balancing potentiometer 50 Operation 66 Torque curves 68 Zero force 50 Subscription service 13 Super capacitor 18 Supervisory control 80 Supervisory Mode 18 20 Synchronous 12 T Threaded base 7 Threaded locking ring 12 16 80 Torque wrench 11 TorqueSwitch 7 61 71 77 80 Reset 72 Threshold torque 62 Troubleshooting 52 Close position 57 Communication 52 Finger closed 54 Finger movement 54...

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