Ball Screws – an Answer to Safe and Efficient Motion for Cobots – Case Study
Collaboration robots (cobots) provide the strength, consistency and reliability of
industrial robots with the judgment and flexibility of human operators. Cobots are
increasingly used in large-scale production applications that involve continuous lifting
operations but still require a human touch. While cobots have been in use for at least a
decade and continue to grow, applications have been limited by the gearing systems
that control motion. A French cobot maker, however, has developed a solution that uses
ball screw and cable actuators instead of gears, setting a new benchmark for cobot
efficiency and safety.
Cobots are increasingly used in large-scale production applications providing the strength,
consistency, and reliability of industrial robots with the flexibility of the human touch.
“While researching applications for collaborative robots, I saw automation in general
was making great strides, but many manual jobs – like sanding — had not evolved for
thirty years or so. This got me interested in developing technology that would assist in,
but not replace, functions that benefitted from human participation,” said Yvan M.
Measson, CEO of cobots producer – ISYBOT.
Building a more efficient workforce
ISYBOT cobots target applications that have not previously been or are difficult to
automate. Cobots augment the human performance in many ways, such as eliminating
fatigue, adding lifting strength, increasing accuracy or improving product quality.
Furthermore, using the cobot restores manual attractiveness, making the worker a
“cobot pilot.”CASE STUDY
For example, the final production steps for manufacturing a passenger train might
require an operator to move a rotary sander around the hull’s surface until it feels
finished to the touch. With cobot assistance, the operator still guides the sanding tool
around the hull surface, but it is the cobot arm that does the heavy lifting. (Figure 1) The
cobot can also learn the path the operator follows, repeating it as many times as the
operator deems necessary.
Figure 1: Yvan M. Measson, CEO of ISYBOT, demonstrates how a cobot can help sand the hull
of an aircraft cabin.
Other ways in which cobots improve productivity and ergonomics might include
assisting in picking and placing parts on an assembly line, assisting with simple batch
operations, or any heavy lifting. Cobots can work with humans and also function
autonomously, improving productivity. (Figure 2). Having the cobot do the most tedious
part of the job reduces strain on the operator’s musculoskeletal system, while freeing
them to focus on quality control. This elevates the role of the operator and helps reduce
Figure 2: In addition to working with human’s side by side, cobots can also work autonomously
improving productivity and ergonomics.
Cobots are often used in industries where workers are constantly required to manually
handle loads of up to 77 lbs or more. These include aeronautics, automotive,
agriculture, naval, railway, defense or manufacturing facilities. Cobots are also valuable
where workers might be exposed to hazardous conditions, such as nuclear plants or
environmentally compromised areas where the cobot can help with the most hazardous
parts of the job.
Building a better cobot
As he studied the market, M. Measson discovered that several other companies were
entering but with solutions he felt were inefficient, cumbersome and potentially
dangerous. The problem, he concluded, was in the gearing assemblies used to
translate electrical energy into controllable motion.
“Gears have high friction ratios and add kinetic energy that, when released, can be
dangerous. They also tend to be quite inefficient in the case of interactive use,” said M.
Measson. “By replacing gears with more efficient ball screws, we drastically augment
human strength and motion safely, consistently and efficiently.”
M. Measson explains that ball screws deliver high strength with minimal friction. His
cobots translate 94 percent of the motor torque into motion. With just electric current,
they can control force for sanding operations or handle loads that would otherwise
require complex gear assemblies and sensors. In addition to being more space- and
energy-efficient, the low-friction characteristic makes ball screws almost maintenance
free and much easier to control.
He says that ball screws have much lower inertia than gears, which, when combined
with the controllability mentioned above, has tremendous safety implications. Unlike
robots, which are usually caged off, cobots work hand-in-hand with humans. They must
be able to stop instantly, for example, on any incidental contact with humans. BecauseCASE STUDY
gears have kinetic energy pent up in their complex assemblies, stopping abruptly on
simple contact is difficult.
Using the best ball screw
Having concluded that using ball screws would enable a highly efficient and competitive
cobot, M. Measson and his team researched vendors and found that Thomson
Industries would provide the best solution for his applications.
“Load capacity is a key differentiator for cobots. Ball screws enable handling of higher
loads than gears, and the Thomson ball screws had the highest load capacity of those
we evaluated. We also liked the fact that they get there with two leads,” M. Measson
Figure 3. Thomson rolled ball screw with a KGF-D standard nut.
Thomson supplied three 12 x 10 rolled ball screws with a standard nut. (Figure 3). The
higher capacity comes from a nut design based on two leads and four loaded turns,
which enables a high load ratio in a very compact component. Moreover, Thomson was
able to engineer the ball screws to leverage the low friction capabilities of balls screws
in at least two ways.
First, where ball screw manufacturers might typically preload the nut and screw to
minimize play, Thomson engineers were able to reduce play without preloading, thus
reducing friction that preloading otherwise introduces. And to reduce friction further,
where ball screw manufacturers might add wipers to protect barriers free of
contamination, the Thomson design resisted contamination without wipers. With no
preloading or wipers, the Thomson ball screws provided the smooth motion the cobot
Also, with inertial ratios of 10802.63 lbf/in2, 10458.42 lbf/in2 and 6724.79 lbf/in2 for each
of the specified ball screws respectively, the Thomson ball screws have among theCASE STUDY
lowest inertial ratios in the industry and provide a fraction of what a geared system
would generate in handling a comparable load.
It’s all about the people
M. Measson is moving forward with many cobots on the production line, all of which are
using the Thomson technology to deliver the low-inertia, low-friction and high-capacity
motion that sets them apart in the gear-based cobot technology market. Most important
to him is the fact that he is not only keeping the person in the process, but he is also
making their work easier.
“When workers first saw the cobots, they were wondering how their jobs would evolve.
But after using them for a short time, they became fans. That is very gratifying,” said M.
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