The U.S. Department of Energy (DOE) estimates that 47% of the electricity used in the non-metal fabrication industries is consumed by motor-driven equipment.
Woodworking machines use power-hungry motors for pumps, fans for dust collection, and in their spindle and servo drive systems.
The DOE recommends a âsystems approachâ to reducing energy consumption. This includes considering the physical components, the application, and processes to maximize the potential savings.
Reducing energy consumption lowers your direct operating costs, controls energy price growth in the market, and is at the same time environmentally friendly.
A Systems Approach to Energy Saving
The motors for pumps, dust extraction systems, and spindle and servo drive systems are the most significant consumers of electricity in a woodworking machine. Additional motors may be found in automatic tool changers and material handling systems. Some energy reduction solutions are best achieved when purchasing new equipment, however, some can be implemented by retrofitting or by upgrading software and processes.
Energy Efficient Components
Using motors that only run when the machine is âin-cycleâ is one way to reduce energy usage. Systems often use induction motors that run at full speed all the time, and that cannot be turned on and off quickly. Replacing these with permanent magnet synchronous motors with intelligent speed control or true servo systems is a good first step to greater efficiency.
State-of-the-art spindle and servo drive amplifiers use low-loss power devices that achieve efficiencies as high as 99%, and the product packaging is designed to dissipate any heat generated outside of the electrical cabinet, eliminating the need for cooling fans or heat exchangers.
Spindle and servo motor speeds are often controlled using pulse width modulation (PWM), and higher PWM frequencies reduce motor iron-losses. High response vector (HRV) control, an advanced form of field-oriented control, closes the motor control loops at a very high rate, allowing faster and more precise motor acceleration and speed control.
The servo motors of a woodworking machine are continuously accelerating and decelerating as the axes change direction during machining. When spindle or servo motors are accelerating, they draw energy from the electrical system. When they are decelerating, their kinetic energy is converted back into electrical energy, which historically has been dissipated as heat in a resistive load in a process called dynamic braking. (See Photo A)
Some DC-bus servo drives may share some of the excess energy with other motors on the machine that may be currently accelerating. Energy may be stored temporarily in banks of capacitors and then released again during drive acceleration. More sophisticated AC drive systems pump the energy back into the main electrical supply, reducing the net energy used. (See Photo B)
Power Savings Mode
The modern laptop computer uses several strategies to save precious battery power, turning off LCD screens, disk drives and other power hungry components on a variety of schedules.
The CNC system includes a powerful programmable machine control (PMC) interface that the machine tool builder can use to implement similar strategies for the woodworking machine. When the machine is not in cycle, the PMC interface can turn off power hungry devices based on a schedule that considers how long the machine has sat idle, and the time it takes to restart each component.
Cycle Time Reduction
When a machine is in cycle, the total power consumed on a per part basis is largely dependent on the cycle time. If parts can be machined faster, the total number of machines required to produce the same output can be reduced, saving energy and other operational costs.
The processing speed of a woodworking machine is often limited by the need to hold geometric tolerances at corners and small radii, or by the need to minimize machine shock when processing small line segments that describe complex curves.
Advanced software in the CNC can look ahead in the part program and take into account the machine's mechanical capabilities and then use advanced acceleration/deceleration techniques to optimize the cutting feed rates in real-time. Smoothing algorithms convert small line segments back into complex curves that can be processed faster by the CNC and reduce machine shock. Combining these strategies potentially reduce cycle times by 50% or more, while maintaining the same part accuracy.
It is often said that you cannot improve something that you do not measure. Todayâs leading CNCs know everything that is going on in the spindle and servo drive systems, including the power being consumed or being regenerated back into the power line. By displaying the electricity consumption dynamically and historically, part programming optimization and other process-related improvements can be evaluated more effectively. With Ethernet connectivity, the data can also be collected into a central database for more detail analysis and comparisons between machines and processes.
Putting It All Together
The systems approach to reducing energy consumption ensures that all avenues are considered. There are success stories of saving 40-50% energy consumption in machine tool applications. It means using machine components designed for energy efficiency, drive systems that recuperate rather than burn excess energy, machine interface implementations that consider power saving modes, and cycle time reduction strategies. Measuring energy consumption enables pragmatic process improvements based on data.
Check with your energy company, local and state agencies as they may provide incentives to invest in energy reduction. By considering energy when purchasing new equipment or when investing in equipment upgrades or process improvements, you not only control costs and maximize your return on investment, but you also make a positive impact on a greener environment.
Mark Brownhill is program manager of the Machine Tool Distributors/Education for
FANUC FA America of Hoffman Estates, IL, 888-326-8287; fanucfa.com.
Note: DOE information reference: United States Industrial Electric Motor Systems Market Opportunities Assessment â Executive Summary
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