Application Stories
Robotics and the Contemporary Controls PCI20U Module
Play an Increasing Role in the Surgical Process
“Robotics in the field of surgery is no doubt taking us
a step forward,” says Jayender Jagadeesan, Graduate
Research Assistant in the Department of Electrical
Engineering at the University of Western Ontario, London,
Canada. “With the cooperation of Contemporary Controls,
my research group is studying the advantages in using the
Mitsubishi PA-10 7C robot in minimal invasive surgery.”
The Mitsubishi PA-10 is a general-purpose
manipulator mounted to a mobile platform with seven
degrees of freedom (DOFs), weighing only 40 kg and
having the ability to pick up items up to 10 kgs due to its
high motor torques. A big part of this ambitious project
was to create an ARCNET® connection between the
manipulator’s controller and the standard personal
computer which required an appropriate ARCNET card.
Since the research group employed the Robot Control C
Library (RCCL) under Windows® OS to control the
manipulator, it was essential to use ARCNET to
communicate between the PC and the controller of the
PA10. Jagadeesan and other research assistants shared
this opinion on ARCNET: “It’s a winning situation.” Why?
Since ARCNET is a general-purpose technology for
network communication, its use in robotic applications has
the advantage that knowledge from other application areas
can be employed to build reliable products according to
the research assistants. “This means open standards to
communicate with robots can be achieved and open
programming languages like RCCL can be applied to
program different types of robots,” they said.
An ARCNET network interface module was not
available from Mitsubishi. However, Contemporary
Controls in Downers Grove, Illinois, designed and
manufactured these cards which ran under Windows OS
as well as other operating systems. As Contemporary
Controls engineers understood it, the PA10 was
supplied with an ARCNET interface that used the
COM20022 ARCNET controller chip, plus the HYC4000
line driver. The HYC4000 is an eight-pin device that
converts the ARCNET analog signaling into an AC-coupled
EIA-485 signal for transmission over twisted-pair cable at
data rates from 10 Mbps down to 1.25 Mbps.
Mitsubishi offered an “Optical Conversion Board
(OCB) designed to replace the HYC4000 line driver—thus,
using fiber-optic cable as the network medium instead of
twisted-pair. It was supplied with an 8-pin header as a
direct pin-for-pin replacement for the HYC4000. The
Contemporary Controls PCI20U ARCNET card
offered the HYC4000 transceiver an option.
Jagadeesan said the initial challenge was to interface
the OCB to the PCI20U. The control of the robot was
accomplished by means of a single PCI20U module
integrated in the robot’s ARCNET architecture. “The
transceiver on the PCI20U was replaced by the OCB with
proper signal polarity and pin identity,” he said. “The OCB
was connected to the servo amplifiers through fiber-optic
cables. This OCB was employed to reduce the amount of
noise and to provide for fast data transfer rates. It
converted the data packets to optical signals.”
The Mitsubishi PA10-7 robot and servo driver are pictured to the
left. The image to the right is the four-layer control structure of
the robot.
Contemporary Controls’ universal-voltage PCI20U
card is compatible with both 3.3-volt (“PCI-X”) and
older, 5-volt computers. PCI-X is an enhancement to the
original PCI Local Bus Specification, enabling devices to
operate at speeds up to 133 MHz. The PCI bus allows for
jumperless configuration and Plug and Play (PnP)
operation. The module operates with either an NDIS driver
or with a null stack driver in a Windows environment. This
device exploits the new features of the COM20022. These
include 10 Mbps communications, the various EIA-485
transceiver options, command chaining, sequential access to
internal RAM, and duplicate Node ID detection.
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However, the robot could be programmed to cancel out
these tremors which which can be considered high
frequency components.”
The Mitsubishi PA-10 is programmed according to how
a surgeon would function in the same condition. “In fact,
most robots being developed in the medical field are the
master-slave type: the surgeon works on the master, while
the robot follows the motion of the surgeon’s fingers,”
said Jagadeesan. “Surgeons and robots like the PA-10 will
continue to work together, leading to more sophisticated
methods in medical applications. This in turn means that
networking components like the PCI20U will continue to
help with these evolving requirements.”
In addition to its many features, the PCI20U module has two LEDs
on the board monitoring network operation and the bus access to
the module. It is equipped with an 8-position, general-purpose DIP
switch which could be used to reassign the ARCNET node address
without removing the module. Ultimately, the node address is
configured via software so the DIP switch can be used for userdefined functions.
In the PA-10 ARCNET architecture, the host computer
acts as the transmitting node and the servo amplifiers act as
the receiving node. The packets are sent in a particular format
from the host to the servo. The servo receives the packet
and decodes the torque value to each of the seven joints of
the robot. There are seven CPUs which individually control
each of the joints, collectively acting as a node in the ARCNET
network. “When a torque command is given to the servo
driver from the computer, the data packet is decoded and the
torque is provided to each of the seven joints for robot
control,” stated Jagadeesan. “The extra degree of freedom
could be used to avoid obstacles and singular points where
the control breaks down. It also has the ability of being
mounted either from the ceiling or the walls, which provides
additional freedom of movement.” He explained that the
robot has three categories of control: 1) Joint-based
control — each of the seven joints is controlled to follow a
desired trajectory, 2) Cartesian control — the robot is
controlled to follow a desired trajectory in Cartesian space
and 3) Force control — the robot is controlled based on the
forces, which are felt at the tip as measured by the 6-DOF
force sensor.
Jagadeesan concluded that there are significant
advantages in employing robots like the PA-10 for minimal
invasive surgery. “Robots help in reducing the operating
time, thereby reducing costs,” he said. “The amount of
trauma involved is far less compared to conventional
surgeries since the incision size is very small, leading to
quicker discharge of the patient. For extremely complicated
surgeries (like operating on babies or performing brain
surgery), it is essential to keep the hand as still as possible
without any tremors. We know that it is impossible to keep
the human hand steady continually.