Industrial Power Tools
8Pages

TECH NOTE ELIMINATE DESIGN COMPROMISES IN INDUSTRIAL POWER TOOLS by Thomas Baile Industrial power tools (IPT) have an operating profile quite different from other motor-driven applications. A typical application requires torque output from the motor throughout the motion. Fastening, gripping and cutting applications have a specific motion profile split into two phases, as shown in the below graph: TYPICAL WORKING CYCLES FOR INDUSTRIAL POWER TOOLS REPEATED CONTINUALLY 100% 80% 60% Speed Torque Speed Phase At first, there’s little resistance as the bolt threads in, or as the jaws of a cutting or gripping tool approach the work piece. During this stage, a motor that operates at a faster free run speed saves cycle time and boosts productivity. Torque Phase Then, when the tool performs the more forceful work of tightening, cutting or gripping, the need for torque becomes paramount. A motor that delivers high peak torque can perform a wider range of tough jobs without excessive heating. These alternating speed and torque cycles must be constantly repeated in demanding industrial applications. Applications will require different speed, torque and duration, calling for a special motor design that minimizes the losses to achieve the best solution possible. It’s even more critical for battery operated devices, which run on low voltage and have limited power available. How to Select and Optimize the Optimum Motor To select and optimize the optimum motor for handheld industrial power tools, we need to first review the motor technology. Let’s consider Brush and Brushless DC motors as our primary selections. Battery powered industrial power tools run on low voltage (12-60 V). Brushed DC motors are typically a good economical choice, but the life of operation of the motor will become an issue. The brushes will see wear because of electrical (due to the current related to torque) and mechanical (due to the friction related to speed) © 2018 Portescap. All rights reser

TECH NOTE | Page 2 factors, limiting the number of cycles until end of life is reached. Brushless DC motors are a more reliable motor solution. They are less susceptible to mechanical wear (no brush friction) and can sustain high peak current (no brushes) during the tightening phase, providing far greater life in the hand tool. Brushless DC motors are better suited than brush DC for industrial power tool applications since they require high speed and high peak current. Brushless DC motors can be constructed in different physical configurations: • n the conventional (also known as inrunner)...

TECH NOTE | Page 3 induction versus copper volume is optimized (slopped curve). Without circulating current, the rotor sees a continuous permeance, therefore a slotless motor doesn’t have any cogging or detent torque. By design, iron losses at high speed in slotless motors are greatly reduced. Copper Wound Coil Slotless Design Slotted Design The slotted design can handle higher temperatures (200 degC) than the slotless design (150degC), thus allowing more torque generation. However, most of the time, the limiting factor in power hand tool usage is the maximum temperature over time (~47deg C...

TECH NOTE | Page 4 Speed phase: the motor needs to run fast with little resistance: u = (U - R * I ) / kt u (Speed in rad.s-1) U (Voltage in Volts) R (Resistance in ohms) I (Current in Amps) kt (Torque constant in Nm/A) Since the torque constant is in the denominator of the calculation, the lower the kt , the higher the speed. This allows more operations in the same time period which boosts productivity. Torque phase: during the second phase, the motor is expected to deliver peak torque at low speeds. As per the laws of physics, the torque is the product of the torque constant and current C...

TECH NOTE | Page 5 Iron losses and speed The iron losses are related to speed. Eddy current losses increase with the square of speed, heating up the motors simply when rotating - even in a no-load condition. High speed motors need special design precautions to limit eddy current heating. Innovation And Optimization of Motors for Industrial Power Tools To provide the optimum solution, Portescap engineers have developed the new Ultra EC™ brushless slotless motors with a revolutionary patented U coil technology. First, copper losses are reduced because unlike a typical slotless skewed winding,...

TECH NOTE | Page 5 Benefits  Greater efficiency of copper turns, minimized joule losses  Optimum package size  Maximized useful volume of copper  Stronger coil integrity  Perfect integration into motor design  Ability to reach a wide range of torque constants Benefits of the Ultra EC Winding in an IPT Application In this paragraph we will review the impact of Ultra EC on motor performances in typical industrial duty cycles. Working conditions: Average duty cycle: free speed during 2s at medium speed Example: pruning shear, nutrunner, gripper, stapler Heavy duty cycle: free speed...

TECH NOTE | Page 6 Average Duty Cycle - Motor Comparison Let’s compare motor performances during the average duty cycle: © 2018 Portescap. All rights reserved.

TECH NOTE | Page 7 We observe higher iron losses, because the speed is doubled. The straight coil (Ultra) is still more efficient (less losses) in comparison with either skewed winding or slotted motor. Conclusion By boosting the speed, the iron losses are quickly going to generate more losses than the copper losses. Therefore, the design of the winding should be tuned for each duty cycle in order to optimize the losses. Thanks to the Ultra winding technology, iron and copper losses are greatly reduced allowing more flexibility for the designer. About Portescap For more than 25 years,...