DS-NOV22-PG49_Layout 1 17/11/2022 15:06 Page 1
GEARS & GEARBOXES
MINIMISING NOISE IN MICRO MOTION APPLICATIONS
Many medical applications demand low noise to enable patient comfort and recuperation, while military devices often need to operate with low acoustic sound for tactical importance. However, within a motion system, the gearbox can be a cause of acoustic noise, so to design a transmission with a low sound output, it’s crucial to understand the factors that impact it. An important cause of acoustic noise is misalignment of the shafts within
the gearbox, on which the gear sprockets are mounted. This misalignment can be traced back to the challenge of maintaining centre distance. Centre distance is the measurement between the centre of two intermeshing gears, and it should be maintained to a predetermined tolerance. However, due to mounting inaccuracies, and misalignment occurring
during operation, centre distance can increase above its predetermined position. In turn, this can displace housing bore positions, as well as the bearings supporting the shafts within the housing. This misalignment causes issues in gear teeth engagement, and these dynamic behaviour changes can result in transmission errors and acoustic noise. To design a
gearbox with low noise properties, a simulation can test the critical factors involved. To vary the centre distance, the housing bore connected to the bearings is displaced at set distances. This simulates the variation
that can occur in manufacturing tolerances, where housing bore position might vary between 30 and 80 microns depending on the production accuracy achieved by the motion system designer. To test and contrast operating conditions of a compound gearbox
comprising three spur gear pairs, analysis should include both load-free and load conditions at 0.5Nm torque. A speed range extending up to 5,200rpm for the gearbox input shaft should also be applied. To replicate the operation of non-linear loads, gear mesh harmonics (distorted voltage waveforms) from first to third order will cover the maximum frequency of 4,000Hz. Misalignment should also be arranged in the skew condition, where the output gear is displaced in the skew direction from the mating gear. This way, noise levels are more sensitive compared to an alternative out of parallel misalignment. The simulation of the displacement of the shaft-supporting bearings
shows that the change in centre distance significantly impacts transmission error and noise levels. The more extreme the misalignment of the shafts, the higher the maximum peak to peak transmission error, as measured in microns. This factor is increased the higher the applied Nm torque load. The more precisely manufactured the gearbox, and the more reliably it can maintain centre distance over time, the lower the transmission error. To understand the corresponding acoustic noise as a result of the
transmission error, a specially set up microphone can capture the output. This is measured in the Decibel A-scale (dBA) as the human ear would hear it, whether on a hospital ward or a military zone. With a no misalignment centre distance condition, the maximum amplitude is 38dBA, measured at 3,200rpm. However, as misalignment skews to 30 microns, noise increases to 50dBA, and at a misalignment of 80 microns, it reaches 52dBA. How the gearbox is mounted within the overall system, and how the
gearbox interacts with it, are also factors impacting transmission error and noise. The simulation can be used to provide analysis on the deflection, considering factors such as alignment and bending, of the system as a whole. Deflection measurement at a system’s maximum load can be identified, as well as understanding if any improvements are required to control deflections by altering the mountings on gearbox, material combinations, or load conditions used in the application. Considering the impact of centre distance on acoustic noise, if a low output
is required, it’s imperative to partner with a motion designer such as Portescap that can achieve the closest tolerances in gearbox production.
Portescap
www.portescap.com NOVEMBER 2022 DESIGN SOLUTIONS 49
FEATURE
A UNIQUE PACKAGE WHICH NO OTHER SERVO GEARBOX SUPPLIER CAN MATCH
PATENTED DESIGNS It starts with design and we have Patented Designs for high performance.
UNIQUE 5 YEAR WARRANTY On our complete range of servo gearboxes and rack and pinion products.
UNMATCHED 2-3 WEEK LEAD TIME On our standard range of planetary and spiral bevel gearboxes and rack and pinion solutions.
ON-TIME DELIVERY OR IT’S FREE! Guaranteed delivery - another industry first for Apex Dynamics. FREE PRODUCT if we are late on what we acknowledged as the delivery date.
ATEX AS STANDARD Apex has achieved Category II 2 GD c T6 classification on our standard gearbox ranges, to the latest ATEX DIRECTIVE 2014/34/EU .
Call NOW for a quote on
0121 227 5340 or email
sales@apexdynauk.com
Patented Designs 5 Year Warranty
2-3 Week Lead Time
Guaranteed Delivery ATEX as Standard
Apex Dynamics Heath House, Cheadle Road Uttoxeter, Staffordshire, ST14 7BY
T: 0121 227 5340 | M: 07305 014551 E:
sales@apexdynauk.com
W:
http://www.apexdynauk.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60
