IMI Zebra Zero Force Manipulator

Since the manipulator arm is the core of the Dexterous Inspection Module, the selection of manipulator arm is important. There are many manipulator arms currently available, however few qualify for use here. The factors considered when selecting a manipulator arm are listed below.

• Coverage of the drum surface by workspace of manipulator arm - The intersection of the manipulator's workspace (within which it can position the end effector at an arbitrary orientation) and the surface of the drum, or a cylinder several inches larger in radius than the drum, determine how much of the drum surface can be sampled and inspected, respectively. Maximizing this intersection will decrease the number of times the lift platform will have to be moved per drum.
  
  
• Power consumption of arm and low-level controller - Obviously the manipulator must be able to run off of the mobile base's power supply, or a comparable DC power supply. This requirement excludes most if not all industrial robots.
  
  
• Weight of arm/controller - Since the manipulator is to be deployed on a mobile base, and lifted to various drum heights, the more it weighs, the more power the base and lift will draw positioning it.
  
  
• Available high-level control software - In keeping with the underlying requirement to use off the shelf components where possible, it is preferable to have a high level programming interface to the manipulator's controller. Although we are capable of developing both the low level and high level software, it is much more costly to maintain low level device dependent software.
  
  
• Cost - Dexterous manipulators can cost from $20,000 per degree of freedom and up, due to their complex nature and their vertical market.
  
  
• Electrically driven actuators - Since the mobile base uses an electric power source, a manipulator with pneumatic, hydraulic, etc. actuators would require an additional power source, adding mass and bulk to the entire mobile package.
  
  
• Force sensor - Tactile feedback is helpful in tasks such as picking and replacing tools, obtaining surface samples, and detecting and limiting collisions.
  
  
• Electric gripper - Many electrically actuated manipulators are sold with pneumatic grippers. There is no pneumatic power source on the mobile base so an electric gripper must be used.
  
  

The IMI Zebra ZERO Force manipulator is manufactured by Integrated Motions Inc. The manipulator is composed of six revolute joints which allow the manipulator to position tools with arbitrary orientation within a characteristic workspace. The Zebra has a six axis force sensor mounted in the wrist, an electrically actuated gripper as an end effector, and is controlled by an HCTL-11 based 8 axis motor control card. The Zebra is controlled from a DOS based PC, which is connected to the operator workstation via Ethernet, with TCP/IP sockets as the software communication layer.

The relevant specifications of the Zebra are listed in the table below.