Efficiency needs a system approach, depends on individual applications

Energy-efficient motion control: To identify the most energy-efficient pneumatic and electric automation, a technology-neutral comparison is required. After considering different alternatives, a German automotive components supplier adopted a ready-to-install energy-efficient handling system.

By Christopher Haug May 16, 2012

When consumers look for an energy-saving washing machine, they simply buy the device with the best energy-efficiency rating. For manufacturers of washing machines, things are more difficult. If they want the most energy-efficient production facility, they realize that no certification of energy-efficiency classes is available.

"Energy efficiency in automation is dependent on the industrial application in question," explained Festo energy-efficiency expert Dr. Axel-Andreas Gomeringer.

The only reason it is possible to classify washing machines into energy-efficiency classes is that the usage scenario of a washing machine as a closed system is precisely known. For example, all devices can be compared easily on the basis of their standard cotton program with a 60 C wash temperature. For machinery and installations, however, the system parameters are not clear. Should only the drive be assessed, or the control chain, or the entire factory?

Define tasks clearly

Any industrial application has its specific requirements for technical criteria such as speed, load capacity, power to weight ratio, accuracy, control behavior, rigidity under load, and efficiency or robustness, and also for economic criteria such as the purchase cost (price, commissioning, installation) and operating costs (maintenance, durability, energy costs). In any application, energy efficiency depends on the specific task. "The task must be clearly defined before the user chooses a drive technology—electric, pneumatic, or a combination of the two,” explained Gomeringer, head of innovation and technology management at Festo.

Intelligent dimensioning

With engineering software, users require just a few key data to arrive at the right solution. Which electromechanical linear actuator best meets requirements? All that is needed is the input of position values, payload, and the installation position, and the software will suggest an optimized solution. This eliminates wasted energy by incorrect sizing.

A common dimensioning process for mechanical drive and transmission components and motors prevents a duplication of safety factors, which would result in oversized electric drive systems and a waste of energy. Calculations have shown that, with consistent use of sizing software, energy costs can be reduced by as much as 70%.

Energy savings in the system

Often success stories about energy-optimal solutions really get started with complete handling systems and control technology. Supplied ready-to-install and fully pretested, lightweight handling systems such as a high-speed handling robot can be delivered directly to users’ applications. The low weight of the robot, with its rod kinematics made up of standard electromechanical components and ultralight carbon fiber rods, ensures the efficient use of drive technology. With a gantry design with wide dynamic motion, stationary motors for the X- and Y-axes ensure lower moving masses. In control technology systems, for example, a double motor controller with coupled intermediate circuits exploits braking energy for recovery purposes.

Smooth handling

The Tripod robot design “needs less space and design time than a handling gantry and is also faster than a SCARA” (selective compliant articulated robot arm). That is how Gerd Ulmer, general manager of G. Ulmer Automation GmbH, summarized some advantages of the new handling system. He has installed two Tripod handling units on an assembly machine for the automotive components supplier.

On a machine that assembles safety relays for diesel engines, two Delta robots equip the relay bodies with seven to nine contacts, depending on the type of relay required. “The components were previously produced abroad and are now—primarily in the interests of better quality—to be produced on a fully automatic machine which includes automatic test stations,” explains the client, a special machine builder. The machine comprises 24 stations and was ordered from Ulmer by a component supplier to the automotive industry.

Quality awareness

The machine comprises stations to test individual components and carry out continuity and high-voltage tests, tests of soldering flux dosing, monitoring of the soldering process, and measurement of the contacts fitted to the relay bodies. “A large number of the assembly cells are test stations, with four integrated vision systems,” explains Ulmer.

Thirteen vibration conveyors feed contacts and other assembly components to the machine. It takes only 90 seconds for the contacts and semifinished relay bodies to pass through all 24 assembly stations and emerge as fully assembled and tested relay bodies in a process that includes spraying the bodies in an injection-molding machine and printing them with the date of production.

“To be precise, the machine produces four finished modules every 30 seconds, since that is how quickly the injection-molding machine processes four workpieces,” says Ulmer, describing the performance of his machine.

Flexible, easy teach-in

With the new design “we have been able to produce around one million relays a year in three variants, working in shifts,” reports the system builder. One of the benefits of the handling system is its flexibility, which is easy to program using a configuration tool in combination with a programming language.

“As we received the revised samples of the workpieces for series production very late from our end customer and needed to carry out all programming in-house, we found the uncomplicated and intuitive programming of the robot system very helpful when it came to modifying the functional sequence and component-fitting position at short notice.”

The controller

Thanks to low moving mass and the high rigidity provided by the pyramid-shaped, enclosed design, the robot handling system is highly dynamic but at the same time more accessible than Cartesian handling systems or SCARA robots. The Tripod is actuated by a robotic controller, which can position tools and grippers in three dimensions. The tool tip is guided along the programmed path at all times, even if the orientation of the tool changes. Operation of the system is made easier by the optional handheld terminal, equipped with a touchscreen and keypad. And what’s more, the controller can be used, for example, to link in vision systems such as an intelligent vision system and also handle moving objects.

Equation of success

Customers’ handling tasks determine the form that a solution takes, regardless of the type of drive. Automation experts can help choose among servopneumatic, electric, or pneumatic—on a technology-neutral basis, working on the principle of “Energy efficiency times mechatronics equals success."

Also read: Technologies used in the Ulmer Automation application


– Christopher Haug is with Festo. Edited by Mark T. Hoske, CFE Media, Control Engineering.