I think the holdup in popularity of hexapods just comes down to the
great capabilities of the more "traditional" type machines. You can
already get a linear drive conventional HMC or VMC with 4724ipm rapids
and 2+G acceleration. At that point, the % of cycle time that's made
up of non-cutting positioning moves is practically nothing. Even with
a high end ballscrew machine, you've already got 1968, 2362, and even
3546ipm rapids with 1-1.5G acc/dec, making the positioning moves a
very tiny % of overall cycle time. For the most part, manufacturers
have quit going above the 1968 and 2362ipm for the last decade,
because the cycle time improvements just aren't there. More time is
spent on spindle starts and stops, tool changes, and rotary table
rotations. Hexapods don't do anything to address those other non-
cutting motions, so I assume that's why they've been brushed to the
back of the R&D pile.
I think the hexapods will pick up steam in the next decade for die/
mold type work, and five axis stuff. Die/mold work, because of
dynamics of that little tiny head blasting around a 3D contour with
very little mass, and you don't need a ton of HP. Five-axis work,
because of the ridiculous speed at which the tool angle can be
At least that's how I see it. Could be wrong!
They seem to have found a niche in sorting, packaging, and pick/place
applications, rather than as milling machines (although there are starting
to be hexapod positioners that are pretty cool: see
Here's an Adept hexapod machine in action:
http://www.adept.com/media/videos.asp?iswindow=true&gid &pidq .
Hexapods are just one sort of parallel kinematic machine; here's a pretty
good rundown on how the sector has shaken out:
Andrew Werby wrote:
Always good to see a post from you. Haven't seen any for awhile, is
there a reason for that?
The above site was informative. Let me copy an excerpt from it that
seems to bear directly on my original question:
=========================================================For the last few decades, the science of parallel robots has advanced
substantially. Hundreds of research papers have been published,
prototypes have been built, and new topologies invented. More and more
researchers have become involved in this attractive domain. But the
field of parallel mechanisms is highly multidisciplinary. The process
of building a successful application requires expertise in mathematics,
kinematics, dynamics, and in many other fields in addition to the
Unfortunately, this fact was ignored by industry. Companies, such as
Giddings & Lewis and Ingersoll, with long-standing expertise in
machining, decided to go it alone. And they have failed with their
hexapods even though they were the first to deliver them to the market.
Indeed, almost no such hexapods have gained commercial success -- they
simply failed to deliver on the promises of superior accuracy.
Overlooked problems such as thermal expansion, vibrations, and system
complexity are but a few of the reasons. The origins of this failure
are at the companies' approach which was not application- but
product-driven -- here is this futuristic six-legged structure used in
simulators, let's turn it into a machine tool.
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.