The cost of most forms of energy is on the rise. Consequently, more attention is focused on how much energy a component, device, product, or equipment consumes. Here are suggestions
to help keep that consumption low.
By Leslie Langnau
Managing Editor – Design World
Consumer appliances have it. European machine tools have it. And if the cost of energy continues to rise, nearly every industrial product, device, or piece of equipment created for the US market may have it too. “It” is an energy efficiency label that tells how much energy the device will use, either on an average annual basis or over its useful life.
As US plants and companies face higher energy costs, industrial buyers may change their feature demands as quickly as car buyers dropped gas-guzzling SUVs and switched to sedans. To avoid getting caught as shortsighted as the automakers, you may want to consider techniques that can streamline the energy footprint of your creations. Here are a few areas to explore.
Energy efficiency as a design component
Industrial electric motors represent the single largest end use of electricity in the United States. The Department of Energy estimates that these motors consume 25% of all the electricity sold.
The way to manage this consumption, according to Baldor Electric, is through motor management practices, proper motor selection, and the use of adjustable speed drives where appropriate. Most ac motors offer a choice in efficiency levels. And most motor vendors follow the Energy Policy Act of 1992 and the NEMA Premium efficiency levels for 1 to 500 hp motors.
Motor selection, purchase and application should be based on life cycle cost, not initial purchase price. According to a U.S. Department of Energy survey, the average service life of an industrial motor is 28 years. Thus, the initial purchase price over the life of a motor will be about 2% of its total cost, with energy usage at more than 97%.
Baldor suggests motor selection should be based on the number of hours the motor will operate. For motors operating two or more shifts a day, select models that meet or exceed the NEMA levels. For motors that operate intermittently or on one shift, standard efficiency motors should suffice.
It is also important to overall energy reduction to evaluate each application requiring a motor. Adjustable speed drives may be added to fans that previously used dampers and a fixed speed motor to control airflow.
Select high-efficiency motors that meet or exceed the NEMA levels for applications that run two or more shifts a day, such as the Super E Gold Family, advises Baldor.
In the machine tool world, energy needs can be cut through finer control of individual axes. Adaptable control and drive systems can impart the needed control. The IndraMotion MTX, from Bosch Rexroth for example, offers such features as axis-specific jerk limitation, adjustable axis speed and accelerations, adjustable path acceleration, and round rapid-traverse movements. These features can reduce energy needs by up to 15%.
Drive regeneration does not have to be expensive. Bosch Rexroth offers a capacitor module that can be added to a system. As energy goes back to a dc bus, it can be stored onto this module. When a machine needs more energy, it can draw energy out of the capacitor instead of drawing it from the main power source.
The Bosch Rexroth IndraMotion MTX controller and drive platform supports up to 64 axes of motion and 12 independent CNC channels. Its CPU can handle precisions to the nanometer range. It also offers short processing and cycle times.
Newer drives also offer features that promote continuous motion control to eliminate unnecessary acceleration and braking, limit jerk, as well as enable automatic or spline based corner rounding. Use of these features can reduce energy needs by up to 60%.
For linear systems, modern roller bearings with low sliding resistance can replace conventional slide guide technology, particularly the heavy-load roller bar guides used in plastic injection molding machines, body presses, and positioning devices for paper rolls weighing several tons. The friction
coefficient µ of the roller bar guides by Bosch Rexroth — without seals — is between 0.0004 to 0.001, compared to approximately 0.1 for slide guides. Use of these guides can save up to 80% energy usage in appropriate applications.
Manufacturers of pneumatic and electromechanical components continually work to remove perceived weaknesses of their respective products in efforts to expand their applicability.
Newer pneumatic components and systems require less power and compressed air consumption. They also often take advantage of hybrid forms of energy. For example, distributing valves through valve terminals gives you the flexibility to use different flow rates. Such an arrangement reduces tubing lengths, which can save up to 50% in compressed air consumption.
In another example, Festo engineers compared the energy efficiency of electromechanical driven gripper systems with pneumatic versions. Their findings indicate that pneumatic systems require little energy for holding and essentially consume energy only during electrical valve actuation. Reducing the average pressure level in the system could reduce energy consumption even further over the course of a cycle.
The company’s servo-pneumatic proportional gripper, the HGPPI, offers energy savings of up to 75% compared with similar servo-electric devices, partly because it can operate with less current than that needed by servo-electric grippers, which require full current in the motor coils for holding.
This gripper is an example of a hybrid device. Through integrated electronics, it monitors the displacement signal and force used to grip. The 3/2-way piezo valves generate pressure in the gripper’s individual cylinder chambers. Three sensors detect this pressure for simultaneous precision control and to regulate force. Hall sensors handle position sensing. All control and communication hardware are in the gripper housing to reduce the interfaces to the pneumatic and electrical supply lines and to the control signal connection for Profibus-DP. It is equipped with a position controller, a displacement encoder, and valves. You supply Profibus and 24 V connections, along with compressed-air supply.
The HGPPI, from Festo, is flexible to its tips thanks to the independent positioning of the two gripper-fingers, which position to an accuracy of ±0.1 mm. Thus, it handles tasks requiring controllable gripping forces for different sized work pieces. Plus, its weight of 650 g shortens cycle times.
Saving energy in production processes
Control is crucial to energy savings in production processes. Controllers can reduce or eliminate unnecessary movement. Take advantage of programming features that let you specify acceleration and deceleration rates for rounding corners, advises Bosch Rexroth. You can obtain smooth drive motion while reducing wasted machine dwell time.
PCs; programmable automation controllers (PACs); and programmable logic devices such as FPGAs, DSPs, or microprocessors can speed changeover times, reduce waste, and increase production throughput, all of which can save energy. But tight integration of multiple intelligent subsystems for motion control, logic, process control, vision, monitoring, enterprise connectivity, and machine-to-machine communication is key.
While Ethernet is viewed as a common thread to tie distributed pieces together, programming communication interfaces with TCP/IP functions is not trivial. In National Instruments LabVIEW 8 and its extensions, local and global variables communicate within and across the software on the same machine, while new shared variables can read and write data among multiple machines across the network. A shared variable is similar to a PLC tag that you can bind to an I/O channel or data value, where it becomes accessible from any intelligent node on the network.
PACs come with a range of features. Opto 22 PACs, for example, have features found in PLCs, distributed control systems (DCSs), remote terminal units (RTUs), and personal computers. For efficiency, choose a PAC-based system that uses distributed intelligence, not just a distributed architecture. Distributed intelligence offloads many control functions to remote processors co-located with distributed I/O. Distributed intelligence shortens wiring runs, reduces network traffic, maintains critical control should communications fail, and frees the central controller for supervisory tasks.
You can connect SNAP PAC components to industrial machinery and equipment to better gage uptime and power consumption, and then configure the controller to shut equipment down when not in use for more energy savings.
Sensors can be the “early warning” system needed to detect problems before they become major issues. When integrated with displays, sensors help create an integrated “intelligence” system that reduces inefficiencies. Flow sensors, for example, monitor compressed air consumption and send the data to cost centers. The arrangement alerts operators in the event of leaks, preventing problems from pressure drop.
Using software tools for energy savings
Each moving mass requires energy. Various design tools from vendors will help you determine how best to manage the tradeoffs of movement and efficiency.
If you optimize the factors that influence a cylinder, you should be able to considerably increase piston speed. Too high a piston speed, however, – particularly in the end positions – can quickly lead to overloading as the energy can no longer be absorbed or discharged by the cylinder.
The result is high impacts, which could damage the cylinder and moving load. The reason lies in the kinetic energy of the total moving load, where the momentum is the product of mass and velocity.
A PAC with distributed intelligence offloads control functions to remote processors co-located with distributed I/O. Distributed intelligence shortens wiring runs, reduces network traffic, maintains critical control should communications fail, and frees the central controller for supervisory tasks.
Consequently, if speed is doubled, the cylinder end cap must absorb four times as much energy. The use of air cushions can absorb eight to ten times more energy than rubber buffers. Hydraulic shock absorbers can discharge up to three times more energy than air cushioning. Of course, each option adds costs in terms of weight and components. Festo offers its Computer Aided Cylinder
Optimization (CACOS) software that accurately specifies pneumatic systems for demanding applications.
The GFDM, also from Festo, is a standard package that monitors air consumption and flow. It tracks leaks and uses the data to evaluate consumption levels. It will manage compressor run time, which can help reduce air consumption. Up to 16 process operations can be monitored on an installation.
Baldor’s Energy Savings Tool (BE$T) program compares the energy saving potential between motors and drives with various energy efficiency ratings then selects the “best choice” for overall savings. BE$T may also be used in conjunction with a PDA to conduct a plant survey of motors. The program automatically selects the equivalent Baldor motor from the description entered. Motors may be evaluated individually or by a list.
The IndraSize program from Bosch Rexroth, systematizes drive design for every application process and reduces energy consumption through selection of mechanical components, definition of the motion process, pre-defined motion profiles for sector-specific applications, and a database with optimal motor and control combinations.
Energy savings through installation practices
Installation often offers an opportunity for “overkill” in that systems can be specified or built too rugged to handle the rare cases that need maximum output. On the other hand, control and drive systems with too little power put energy strains on a machine. Careful attention to the application will help avoid these extremes. Unnecessary components add mass and weight to a machine, which requires the use of more powerful drives, which in turn consumes more energy, adds Bosch Rexroth.
Pay attention to friction. Select products, where applicable, which use anti-friction recirculating ball bearings. Take advantage of low friction efficiencies found in linear systems with slides, dovetail type slides, or bronze on steel pads.
With bearing preload, it is not always necessary to default to the highest accepted value. That value often requires the use of additional seals and other contacting components that may be unnecessary. For example, if a system will be installed in a clean environment, you can safely configure it with fewer components.
The above developments are only a few of the many possibilities vendors are working on to aid the task of managing energy consumption. Stay tuned for more developments as they are introduced.
The following companies provided material for this article: