Pittman gearmotors help TUG robot make hospital rounds

  • December 19, 2007
  • Ametek
  • Case Study
December 19, 2007 - The TUG robotic indoor transport system pioneered by Aethon Inc. (Pittsburgh, PA) is a uniquely automated courier system making the rounds in an increasing number of hospitals nationwide. The robot can deliver and track instruments, medications, meals, and lab specimens anywhere in a facility (even traveling from floor to floor via an elevator). Paired with a suitably equipped distribution cart, TUG works around the clock and navigates autonomously to help eliminate repetitive and mundane tasks, reduce costs, and improve staff productivity.The enabling technology is both customized and complex, integrating microprocessors, touchscreens, infrared and ultrasonic sensors, and controllers. Direct-driving each of the robot’s two wheels, PITTMAN Series 9000 brush-commutated DC gearmotors have delivered the reliability and control prescribed by the design team.“Our application is notably aggressive and we run the motors hard,” reports Spencer Allen, chief technology officer for Aethon. “Our system can only thrive with quality, cost-effective motors” offering the ongoing capability to satisfy inherent requirements for high acceleration and deceleration.Even with payloads as heavy as 500 lbs., TUG must be able to stop appropriately should a route be temporarily blocked. A unique Light Matrix sensor system engages a series of infrared and ultrasonic “whiskers” to detect objects such as beds, doors, IV poles, and people in TUG’s path. Upon sensing any obstacles, the robot slows and then stops. TUG announces “waiting to proceed” and nimbly navigates around the object or person.In turn, the planetary gearmotors make the grade. According to Allen, they promote “better control and an optimized balance of maximum speed and torque” due to their 24:1 reduction ratio, which ultimately allows them to run faster and provide increased torque at the output shaft. The speed at TUG’s wheel shaft can reach 130 rpm.Planetary gearheads typically will be specified for high-torque applications since their multiple rotating-gear design serves to increase torque load-carrying capability. They tend to be more robust with higher accuracy and lower backlash than spur types and prove especially well-suited for higher-load applications in small packages.Allen confirms these gearmotors “contribute to a compact assembly” within the smallest possible design envelope. (These gearmotors measure 6 in. long.) Further making life easier during manufacturing or service, each integrated wheel-and-motor assembly is supplied as a “drop-in” module bracket-mounted to the robot.Few gearmotor modifications were necessary to meet TUG’s application demands. Most notably, a 19V armature (instead of 24V) was specified with the purpose to achieve higher torque capability.As is the case with all PITTMAN brush DC gearmotors, the 7-slot armatures have been skewed to minimize magnetic cogging; two-pole permanent magnet stators have been constructed with ceramic magnets enclosed in heavy-gauge steel housing; and brushes have been made from copper graphite.Brush assemblies have always been potentially problematic within the motor industry, since the documented primary cause of failure in brush-commutated DC motors over time is ongoing brush wear caused by the interface between brush and commutator.The PITTMAN motors provide a value-added advantage using cartridge brush assemblies. These house brushes within a specially designed cartridge and incorporate torsion springs to promote even force over the life of a motor, resulting in less rapid wear.The traditional method for mounting brushes in DC motor assemblies has been to solder the brushes onto standard cantilever springs to enable the required constant contact with the commutator. The conventional spring design, however, exhibits inherent drawbacks as force levels diminish over time, often resulting in premature motor failure.The cartridge brush assembly fits into the motor base and consists of a two-piece, high-temperature plastic snap-together assembly in which each of two brushes is seated securely within its own specially constructed slot. This cartridge design restricts the brushes to traveling in a track in a desired linear motion and provides for an ideal region of pressure for brushes to withstand the detrimental effects of mechanical wear.Before a TUG system is installed in a hospital, advance work gets under way. Aethon engineers map the landscape corresponding to the areas that the robot will traverse and then designate a “home base” location (such as a pharmacy or central supply). State-of-the-art and patented navigation software accommodates a facility’s layout, bypassing any need for costly modification or construction.When TUG is up-and-running, all systems are “go.” Hospital staffers at the home base can respond to supply requests by loading TUG with the needed goods or items, select the destination using a touchscreen interface, and then send TUG on its way. All along, the touchscreen grounded at home base displays a map of TUG’s location for tracking every delivery at all times.Proprietary communication software allows TUG to operate elevators and automatic doors and deliver to closed areas by ringing a doorbell upon arrival. Allen adds that the gearmotors run quietly, which is a vitally reassuring outcome in sensitive patient settings.“TUG has certainly benefited from innovative technology,” Allen notes, “and PITTMAN gearmotors have helped keep us on the move.” Learn More

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