Actuator : Demining Innovations
Lee Felsenstein and Steven E. Saunders, Ph.D.
Issue 4.1 | February 2000
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a conceptual 4-pole system driven by power from two stationary bicycles. Straight
broken lines indicate the extent of the parcel of land to be probed. The actuator
is suspended at the juncture of four cables extending from the corner poles.
Pulleys conduct these cables to the rectangular housing containing the electromechanical
parts, including the clutches operated by the microprocessor. Power is transmitted
to the actuator through a wire suspended from the near pole along its cable.
A protective earthen berm (curved solid and broken lines) is shown cut away
to expose the elements at the near pole.
c/o L. Felsenstein, T. Wright, E. Brechin. Caption c/o Felsenstein and Saunders
to humanitarian demining differs from generally accepted methodology. It has
not yet been tried, and the purpose of this article is to ensure that the
general concept is placed in the public domain, where it may be debated and
modified without considerations of intellectual property. Interval Research
Corporation, where this idea originated, is not in the business of mine clearance,
or of manufacturing mine clearance systems, so the idea is being passed along
to the community best capable of analyzing it.
Mines are built
to destroy themselves when triggered by an external event. If we can simulate
the triggering event adequately, we can clear an area of mines by detonating
them on site. For anti-personnel mines this means simulating the tread of
humans to the necessary degree of impact and repetition. During this process
the system used must not be seriously damaged by the detonation of mines,
and operating personnel must be kept safe.
with John Walker's concept of "Moore's Law in the Minefield," http://www.fourmilab.to/minerats,
our system is intended for local manufacture and assembly using one or more
high-technology components produced in high volume at low cost. Our concept
differs from Walker's semi-autonomous "mine-rat" robots in that
ours is a stationary system erected on a parcel of land able to probe the
entire surface of the parcel to an arbitrary degree of fineness.
opposes on site detonation. Attempts at clearance by flails and similar devices
have proven unreliable and likely to render unexploded mines hypersensitive.
It is our observation that those devices are relatively expensive and are
typically applied to the task for a short time under control of skilled personnel.
We propose instead a system that works over a much longer period of time under
control of local personnel using local energy sources.
The system we
envision would consist of three or four well-braced upright poles holding
pulleys on a plane above the mined ground. Positioning cables feeding over
these pulleys would join at a central point, where the "actuator"
would be suspended. This actuator serves the function of probing using a weight
to simulate the human triggering effect.
systems such as this have been used for positioning cameras over large open
and the use of such a system in a demining application is described by Havlik
and Licko (See vol. 2.2 of The Journal of Mine Action article Humanitarian Demining: The Challenge for Robotic
methods of actuation are possible. One might be a bundle of chain mail raised
and dropped repeatedly. Another might consist of a water-filled bag made of
cheap plastic drawn or rolled across the surface. We claim no expertise in
actuator design and recognize that optimum actuator design will not be determined
without extensive testing. Power to operate the actuator would most efficiently
be transmitted mechanically by additional pulleys run from the poles.
principle of operation is that the control module knows the position of the
actuator on the horizontal plane at all times, probably through electronic
sensing of cable extensions as processed through simple trigonometry. The
control module would contain dedicated microprocessor controllers operating
on input signals from sensors located on the suspension poles. The poles then
control the electrical actuation of clutches, which apply prime motive power
to the positioning cables.
The 'closed loop'
is formed by the path from cable extension sensors through the microprocessor
and its software, to the clutches and to the extension of the positioning
cables. Reference monuments would be necessary to allow the system to recalibrate
itself, given the inevitable shifting of the poles. The software controlling
operation would be built into a protected control module in the form of read-only
memories (ROMs). The control module would be built to move the actuator successively
over every element of the surface below it, and to remember the last point
at which the actuator probed. The operators would have a few commands; start,
resume, recalibrate, and stop. The operators may choose to run the system
through as many complete passes over the mined land as they desire.
power for the system need not be electrical. A shaft would be provided which
may be turned by whatever power source is available. The operation of the
shaft would generate sufficient electrical power to operate the control module
and its clutches, in addition to mechanically performing the shift, drop and
lift functions of the actuator. Persons involved in the operation on site
must, of course, be protected from the fragments generated by mine detonations
by beams or similar obstacles.
This system is
intended to take advantage of economies of scale and the low cost of local
labor. It should be distributed by a multi-tiered system involving training
of local personnel in the process of installation and maintenance, and in
the training of on-site operators. Control modules and other high-tech components
would be contracted for and distributed by organizations having an interest
in promoting mine clearance at low cost. Lower-technology items would best
be manufactured locally, and tools and training may constitute the imported
items in this case.
of the control modules would best done either by one concern (thus maximizing
the volume of units over which to amortize expenses) or by a number of smaller
concerns building to a standardized design, thus allowing for price competition
(although quality would have to be monitored rigorously). The design of such
a system, capable of being built from varied locally-sourced materials and
operated by minimally-trained personnel, will not be a simple task. Achieving
the necessary reliability of operation from the controller components will
require the application of software design techniques perfected in the automotive
It may be appreciated
why no benefit would accrue from patenting or otherwise protecting the general
system design, since assembly of the system would take place far from any
mechanisms for enforcing such ownership. The systems should, we believe, be
paid for and owned by the local people or community whose land is being cleared,
so that the effects of proprietorship will be manifest. The "sale"
of the system components (which will be partially subsidized) should, we believe,
include an agreement to resell at controlled prices, perhaps through the agency
handling distribution and training in the local country. In this way the allocation
of the components goes first to the locality that can raise the initial price,
which is then refunded (less depreciation) by the next purchaser, and so forth
until the components wear out. This would, we hope, be a long time, given
that each user sees the components as valuable property to be protected from
depreciation and sold off as soon as its local use is complete.
Some might object
that we are postulating a billiard-table environment whereas the real world
is much more complicated. We acknowledge, of course, that paths will have
to be cleared manually to allow the erection of this system on mined land.
It is less difficult to demine manually a linear path than a whole field.
The presence of brush overgrowing the minefield is an obstacle that can be
addressed by fitting brush-clearing attachments to the actuator so as to allow
for safe removal. Manual control of the actuator movement may be necessary
for this phase.
We also acknowledge
that our proposed system will not clear mines in all terrain and circumstances.
But we believe that it can be greatly useful in clearing mines in a large
number of locations, thus freeing human resources to clear mines in more difficult
Demining is tedious,
life-threatening work, which requires that every bit of the field be swept
or probed. What better task to pass to a machine, given that computers are
only good at tedious, repetitious actions? And why not let the mines blow
themselves up if only the machine will feel the blast (and be easily and cheaply
repairable)? To the design philosophy (now stylish in Silicon Valley) expressed
by the phrase "fast, cheap, and out of control," we counterpose
a different ethos of "slow, cheaper, and highly repetitious," which
will better serve those who live with antipersonnel mines in their ground.
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