July 08, 2009      

Barrett Technology has a well deserved reputation for producing the highly advanced (and highly regarded) robotics arms and hands–the Whole-Arm Manipulator (WAM) and BH8 BarrettHand, especially. Barrett’s third product, the Ultra-Miniature Brushless ServoElectronics Module, or “Puck,” is less well known, but Robotics Business Review believes that a standalone, commercial version of the Puck servocontroller is truly transformational technology that will advance the robotics industry as a whole and greatly increase the number and range of robotics applications.

Human Centered Robots
Privately held Barrett Technology was spun out of work that CEO Bill Townsend began while working on his Ph.D. at the Massachusetts Institute of Technology’s Artificial Intelligence Laboratory. Townsend completed his degree in 1988 and founded Barrett soon thereafter.

Barrett Technology produces a number of innovative products that are in keeping with the company’s overall mission to create technologies that allow for the development of human-scale robot manipulators that can work in close association with people safely and efficiently. Townsend says the company will achieve this by achieving new levels of performance and human interactivity.

To date, Barrett Technology has developed three products: Both the Whole-Arm Manipulator (WAM) and BH8 BarrettHand, are highly regarded within the robotics community and are fully productized. The third, the Ultra-Miniature Brushless ServoElectronics Module, or ‘Puck,’ is less well known, but has the potential of becoming a truly transformational technology.

WAM Arm
For robotic arms to coexist with humans they must be extremely safe, particularly during instances of collision or unexpected force exertion. Attempts have been made to increase the safety of conventional industrial robotic arms by covering them with impact absorbing protective material or by adding force/torque sensors to systems, but these efforts have met with less than optimal results, particularly under real-world operational conditions.

Industrial robot arms, designed to work in highly-structured, enclosed work areas, focus on preprogrammed movement and positional placement of their end effectors, with little regard for the movement and forces applied to other sections of their arms. Forces applied to the end effector, or any other place on the arm, do not affect the movement of other sections of the arm (e.g. drive motors are unaffected by forces applied to the arm). This makes industrial robot arms inherently unsafe for applications that require close contact with humans.

Barrett Technology’s Whole-Arm Manipulator (WAM arm), first introduced in 1988, senses and controls forces over the whole arm (thus the name). From the beginning, the requirement to provide good ‘backdrivability’ was the key design factor in the development of the WAM. For this discussion, backdrivability refers to the capability to control the whole arm by manipulating the end effector (or other arm parts).

Unlike industrial robots, forces applied anywhere along the WAM arm affects the drive motors (velocity, position, and torque sensors are used at each of arms’ axes), allowing the arm to respond appropriately when it comes into contact with other objects (“joint-torque controllable” in technical parlance). The result is improved control and safe operation.

Backdrivability also opens the WAM arm to additional areas of application. For example, the WAM was one of the first devices to support haptic control technology (Haptics is the science of using touch feedback mechanisms to control computer/robotics applications.)

Another distinguishing feature of the WAM arm is that it does not use the typical gear-based system of power transfer. Instead it relies on a gear-free cable-and-cylinder drive system. Cable drives offer low friction and provide for the smooth transmission of torque from the actuators to the joints. Low friction, plus a number of other technical advantages associated with cable driven systems, such as the elimination of the ‘backlash’ inherent in geared systems, result in quick, smooth joint movement.

The WAM arm comes in two primary configurations, one with four degrees-of-freedom (DOF) and one that adds a 3 DOF wrist to the base configuration for a total of seven degrees of freedom. The basic arm provides four degrees of freedom equaling those of the human shoulder and elbow, but providing each joint with a greater range of motion.

Incremental technological improvements have been incorporated into Barrett’s WAM arm over its 20 year development. Key advances include the addition of electronic circuitry specifically designed to ensure safety by monitoring power flow, for example, and the reduction in the total power used by the device to amounts safe for humans. The latter involved the elimination of external controllers, along with the cables running to and from the arm and controller cabinets, as well as the cooling fans for the cabinet (see The Puck, below).

According the Barrett, under normal conditions, the WAM arm draws an average of 40 watts to 50 watts, less than the power draw in a typical residential floor lamp. In addition to the safety factor, the low power requirements of the WAM allow it to operate effectively while powered by batteries. Other advancements include a reduced footprint, improved reliability, increased precision, and automatic tensioning of drive cables.

While Barrett does not release WAM sales figures, it does point out that the arm sales have increased steadily over the last few years. According to Barrett, 2007 was a banner year and 2008 doubled the 2007 sales figures. Even with the current worldwide economic downturn, 2009 WAM sales have on course to exceed those of 2008.

Barrett has customers in over twenty countries, including research universities like MIT, Harvard and Northeastern, as well as Global 2000 companies such as Honda and Sony. Barrett Technology also licensed several WAM arm technology patents to Z-Cat Inc., the parent company of MAKO Surgical Inc., a developer of haptically-guided knee surgery system. In 2006, the MAKO/Z-KAT Haptic Guidance System was approved for use by the U.S. Federal, Drug, and Food Administration (FDA). Barrett Technology has indicated that they are exploring a number of vertical market segments in which to sell WAM arms. Manufacturing and additional healthcare robotics applications would seem to be logical choices.

The BarrettHand
Barrett’s BH8 series BarrettHand is designed with an approach similar to that of the WAM arm, but is a distinct departure from its industrial robotic counterparts both in terms of technology and overall approach.

Industrial robots make use of a variety of end effectors and grippers. Each is specific to a given job, and the changing of such is time consuming and costly. If specialized effectors or grippers are required, they must be custom manufactured.

Barrett’s approach eliminates the need for multiple attachments in favor of one gripper that is suited for a range of applications, which also lowers the total cost of manufacture. The BarrettHand features a multi-fingered programmable grasper that can securely hold objects with a variety of sizes, shapes and orientations. The dexterity the BarrettHand provides greatly increases the scope of application robotics can be used for, many of which cannot be undertaken using conventional industrial robotics grippers.

The BarrettHand employs three articulated fingers surrounding a circular ‘palm.’ One finger is fixed, while the remaining two fingers can rotate up to 180e? around the outside of the palm. Each finger has two joints. Although the hand boasts of a total of eight joints (eight axes), the hand is controlled by only four brushless-dc motors which are located in the wrist section. The palm contains the hand’s five microprocessors, sensors and signal processor.

A full technical description of the grasping mechanism of the BarrettHand is beyond the scope of this article. Suffice it to say that when the hand closes, the hand’s three fingers and palm act in a coordinated fashion to grasp objects.

Each of the three fingers (two joints per finger) is powered by a single servomotor, allowing the fingers to open and close independently. When closing, if the section of a finger closest to the palm touches an object, the second part of the finger (the fingertip) continues to close until it also is in contact. Therefore, the hand can have up to seven points of contact with objects (the palm and plus two for each of the three fingers). In this way, the hand supports a wide variety of grip patterns and is designed to securely grasp randomly oriented, irregular objects.

Puck
Barrett Technology is best known for its robotic Barrett Hand and WAM arm, but that might not be the case in the future. Beginning in 2005, Barrett Technology began incorporating a small, high-performance servomotor controller of their own design in all of their WAM arms. The device, known as the Ultra-Miniature Brushless ServoElectronics Module, or ‘Puck,’ is based on design work accomplished in partnership with NASA, as well as grants from the National Science Foundation and the U.S. Department of Energy.

According to Townsend, work on the Puck has been going on for about 15 years, though during the last five years development has “really intense.” The intention of the Puck research and design work has been to develop the world’s smallest and most power efficient, high-performance servomotor controller. In this they have succeeded.

The Puck is a full featured brushless servo-controller. The device is exceedingly small, particularly given its functionality. Resembling a miniature version of its namesake – a hockey puck – each Puck weighs in at 43g and measures only 35 mm in diameter and 17 mm in height. Although small, the Puck provides all of the functionality to control and drive a servomotor. In the WAM arm, a Puck servo-controller is mounted on each drive motor. The Puck provides encoding, control, signal processing, sensing, communications and a number of other functions for its associated motor. Barrett Technology has basically combined a controller and encoder, plus other technology, inside a solid, miniaturized, heat dissipating ‘puck’.

With the Puck controller, Barrett has eliminated the need for the external controllers and associated cabinet and cabling, along with the noise, signal degradation and other reliability problems associative with extensive wiring. Moreover, they did not simply move the controller electronics into the arms themselves. Open up a WAM arm and you little more than wiring. The Puck handles everything else.

Feedback from WAM installations incorporating Puck controllers has been extremely positive. So much so, that in 2007 Barrett won a $500K grant from the National Science Foundation (NSF) to commercialize the Puck. The grant will be used to drive costs out of the device (currently priced around $1000), including research into bulk manufacturing (to reduce its price), as well as engineering the module to make it usable in a wide range of brushless servomotor applications.

Barrett Technology issued a press release announcing the NSF grant, but other than the release and a few other mentions in the industry press and academic articles, information regarding Barrett’s Puck is lacking. This is by design. While the product is not under wraps, Barrett is refraining from hyping the technology while they work to broaden its applicability and get the Puck’s cost down.

Conclusion
With their WAM robotic arm, BarrettHand and Puck servocontroller, Barrett Technology has made available to the market advanced robotic technology that makes it possible to create wholly new classes robotic applications. Taken as a whole, Barrett’s products all work to dramatically to increase the versatility and dexterity of robotic arms and hands, but with the requisite emphasis on safety that is in keeping with Barrett’s vision for human-centric robots. While Barrett’s WAM and BarrettHand are best-in-class robotics technology, Robotics Business Review believes that a standalone, commercial version of the Puck servocontroller is truly transformational technology that will advance the robotics industry as a whole and greatly increase the number and range of robotics application.

Resources
Barrett Technology – www.barrett.com