Worker-Friendly Robots


Image: Universal Robots

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A new generation of low-cost robots handles short runs in tight quarters. With so much attention focused on driverless cars, package-delivering drones, and scrambling, stomping, and slithering automatons, industrial robots remain mechatronics’ blue collar guys. They work several shifts each day, no complaints, doing the same repetitive job quickly and accurately.

“That’s the equation that generates high ROI from robots in automotive and electronics mass production,” said Ed Mullen, national sales manager for Universal Robots. “But the other half of the world consists of small- and medium-sized factories that don’t run on that model. They do short product runs with quick changeovers, and can’t justify spending a lot of money for a machine that bolts into place and does only one thing.”

Universal Robots is one of several firms developing robots for this emerging market. It has more than 3,000 robots up and running, mostly in Europe. Another notable contender is Rethink Robotics, which was founded by iRobot innovator Rodney Brooks.

Their robots have several characteristics in common. They are affordable (Universal’s UR-5 lists at $34,000). They need little or no maintenance. They swap grippers rapidly. And they are flexible.

Most technicians learn to program one within a few hours, teaching tasks by moving the arm through each motion, much like a parent teaching a child to swing a bat. The robots then optimize the routines as they learn on the job. This makes them flexible enough to move from line to line, loading lathes one day and assembling housings the next.

The UR-5 robot handling packs of cream cheese at a dairy. Image: Universal Robots

Perhaps most important is that these new robots are built to work safely around people. Most heavy-duty industrial robots are not. Many industrial robots lack collision sensors. All work behind barriers to keep people out.

Even so, the U.S. Occupational Safety and Health Administration has counted about one industrial death by robot every year for the past 31 years. Most of them occurred on lines where people worked near robots.

Universal’s six-axis robots are built to collaborate with people, and 80% of them do not work behind barriers. This is not because they are slow. While Universal’s largest robot, the UR-10, only handles loads of 10 kilograms, it moves at speeds of 1 meter per second. That’s fast enough to cause some damage, especially when handling hard or sharp objects.

Universal uses a grab bag of engineering tricks to keep that from happening. The robot is equipped with force sensors, which trip the control system when they reach 150 newtons (33.7 pounds force), a number referenced in several standards for human-friendly robots.

The control system sends the message to each of the arm’s six Kollmorgen servomotors (one for each axis). Because they are oversized when compared with their loads, they decelerate rapidly to a stop. Because the motors are linked to harmonic drives with 100:1 gear ratios, the deceleration takes place even faster than if the motor were connected directly.

Mullen recommends that factories program robot speed based on their own safety assessments. In the past, when users wanted a greater margin of safety, they slowed down the robot. Universal’s new third-generation robots let users select shutdown impacts below the previous 150 newton set point.

The robots now reaching the market from Universal and its competitors represent a new revolution in shop floor robotics, because they make robotics more affordable for everyone. Mullen said the typical customer receives a payback in six months.

“If you buy something like a gantry, it can only be as productive as the line you install it on,” he said. “But with our system, you can move it to a busy line today and a busier line tomorrow. You get your payback by keeping that thing in production all the time.”

Now, small shops can do it because they no longer have to fear injuries.

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But with our system, you can move it to a busy line today and a busier line tomorrow. You get your payback by keeping that thing in production all the time.

Ed Mullen, Universal Robots


September 2014

by Alan Brown, Associate Editor, Mechanical Engineering Magazine