Standard BH8-SERIES System Components
The Hand
The BarrettHand™, shown in Figure 1, has three fingers labeled F1, F2 and F3. Two of the fingers, F1 & F2, rotate synchronously and symmetrically about the base joint in a spreading action. The “spread” motion around the palm allows “on-the-fly” grasp reconfiguration to adapt to varying target object sizes, shapes, and orientations.
Aside from the spread motion, each of the three fingers on the BarrettHand™ feature two joints driven by 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-independent.
The BarrettHand™, shown in Figure 1, is equipped with a threaded base for compact and secure mounting. The threaded base is fully compatible with the BarrettArm. And, with the arm adapter, it can be mounted on virtually any robot with a standard ISO tool plate, for easy installation and maintenance.
Figure 1: BarrettHand™
Power Supply
The Power Supply for the BH8-SERIES, shown in Figure 2, can be plugged into any regular AC power source. It provides DC motor bus power (24V), electronic component logic power (5V), and supports RS-232 communications between the host 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:
- Line Cord supplying AC line voltage.
- Serial Cable supporting RS-232 communications from the host computer.
- Hand Cable which carries DC power and RS-232 to the BarrettHand™.
Figure 2 - BarrettHand™ BH8-262 24-Volt Power Supply
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 motor power. This cable is durable and flexible, allowing the BarrettHand™ to be used on any robot with minimal effect on robot performance. Use the included set of adhesive guide clips for cable management. Since the control electronics reside inside the BarrettHand™ itself, no other electrical cabling is required.
Figure 3: Cable Connections
Lab Bench Stand
The bench mount stand for the BarrettHand™, shown in Figure 4, is ideal for off-arm development. The durable Lexan® stand comes complete with cable management clips and mounting features to hold your BarrettHand™ unit securely on any flat surface. Non-slip rubber feet keep the stand from sliding during testing and programming. A threaded locking ring for base mounting will secure the hand to the stand.
Figure 4: Lab Bench Stand
Control Software and Firmware
The BH8-SERIES System control software consists of:
- BarrettHand™ Control GUI application and API,
- Firmware (latest *.s19 file), and
- Example and demo programs.
BarrettHand™ Control GUI The BarrettHand™ Control 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” button). See the BarrettHand™ Control GUI Manual for more information on the using this application and the requirements.
C++ Function Library The BarrettHand™ C++ Function Library is an API for programming the BarrettHand™ using the C++ language on IBM-compatible PC’s without having to manage various communication and timing issues. The library contains a hand control class that has easy-to-use functions that permit the use of Supervisory and RealTime commands in software developed by the user. All of the functions are available when the library and its dependencies are linked to the program. Dependencies are usually installed by default so the user can focus on development. The C++ API includes HTML generated documentation that describes all of the classes, variables, and methods that users should use in detail and gives examples.
The API is written in C++ and compiled for 32-bit versions of Ubuntu 9.10 and Windows XP. It is a typical C++ library, providing a class from which you instantiate one BHand object and use it for all communications. The library uses a multithreaded mechanism for sending commands, which allows both synchronous and asynchronous access to the low-level thread and ensures that all communications are executed with high priority. The low-level thread manages all input and output buffers and makes controlling the BarrettHand™ easy.
Firmware 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.
Maintenance Kit
Included in each BarrettHand™ package is a maintenance kit which includes the following:
- Mobil 1® synthetic grease lubricant in syringe
- Hex Wrench Kit (1.0 mm, 1.27 mm, 2.0 mm, etc.)
- 2 mm Hex Driver
- Torque wrench
- Loctite 222
- Tweezers
- Pull tool
- Finger Angle Fixture
- Phillips Head Screwdriver
- Flathead Screwdriver
- 2 Screws with O-Rings
System Options
Arm adapter
Barrett Technology provides an arm adapter (Figure 5) matching the make and model of any robot specified by the customer. This lightweight arm adapter is made to work with the end-effector bolt pattern on your robot, allowing quick, easy mounting and wire management for a BH8-SERIES System. The arm adapter is bolted to the end of the robot arm and the BarrettHand™ is secured to the arm adapter with its standard threaded locking ring. The arm adapter is also equipped with an anti-rotation feature to prevent rotation during operation.
Figure 5: Arm adapter
Strain gage Joint-Torque Sensors
Barrett Technology offers a factory-installed torque sensor for the BH8-262 System. This sensor measures the torque 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 strain gage property 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.
