Gear and gearbox optimization software

Excel-Lent software, from a longtime builder of gears and gearboxes, quickly determines optimum gear parameters for various industries. The developer says it cuts hundreds of engineering hours off projects. Interested users can download a demo to see how easy it is to design a new gearbox.

The most interesting section to design engineers will be “Design”. With minimal input, the program will calculate the number of teeth in the pinion and gear, DP or Module, face width, and other factors required to transmit the power, and within a few seconds. The calculated data can be exported to the “Analysis” section for complete examination by picking the “Transfer Data “ tab on the screen. The calculated capacity will be close to the required power and on the first try.

Also, the software’s dimensioning program may be the most versatile available. Non-standard center distance or matching a new gear to an existing gear is as easy as clicking the indicated option. The material tables list all commercially available materials, with heat treat and mechanical properties so users can choose any gear material to fit their need.

In all three sections, sample input data are stored for users to get started. Click on Samples to open a table of examples. Selecting one of the samples fills the input screen with data. To run the sample select“Calculate”. The developer says it welcomes comments and suggestions regarding the our software at any time.

In response to the gear market’s need for optimization software, which has been lacking for many years, Excel-Lent gear and gearbox design and analysis software has been developed by Excel Gear, Inc., Roscoe, Ill. The software is written in Visual Basic.Net by engineers who also design and manufacture gears for their own use, according to company president N.K. “Chinn” Chinnusamy.

“Although commercial software has long been available in the gear industry, it has been too expensive or too complicated for engineers without specialized gear design knowledge,” say Chinnusamy. “Our software is specifically designed with a user-friendly interactive input screen providing defaults and options in accordance with the AGMA 2001 standard (American Gear Manufacturers Association).” Software users can easily navigate through the input screens to edit, analyze and produce reports on the optimum gear and gearbox design for various industrial and other applications.

“This software is not designed for any specific industry,” adds Chinnusamy. It can be used for machine tools, heavy materials handling equipment, even the wind-turbine industry. For the wind turbine industry, for example, the designer needs a full understanding of all the operating loads on the gear members to arrive at the required power rating.

The key calculations performed are the AGMA power rating and load calculations, including bending strength geometry factor (J) and pitting resistance geometry factors (I). Output from the software is a single page of data printed in a format that is easy to read and interpret. Other commercial software typically prints five or six pages of information, which may be confusing to most design engineers unless they are gear experts, says Chinnusamy.

The users of Excel-Lent need not be familiar with AGMA standards to use this software. Those who are not gear engineers can also benefit from the gear engineering knowledge embedded in the software package.

For further information, a test demo, pricing and purchase of this software, please visit www.excel-lentsoftware.com.  

EXCEL GEAR INC.
www.excel-lentsoftware.com 

Software helps design better gears – even for wind applications

In response to the gear market’s need for optimization software, which has been lacking many years, Excel Gear Inc, Roscoe, Ill., has developed Excel-Lent gear/gearbox design and analysis software. This program is written in Visual Basics.Net by engineers who also design and manufacture gears for their own use, according to company president N.K. “Chinn” Chinnusamy.

“Although commercial software has long been available in the gear industry, it has been too expensive or complicated for use by engineers without specialized gear design knowledge,” says Chinnusamy. “Our software is specifically designed with a user-friendly interactive input screen providing defaults and options in accordance with the AGMA 2001 standard.” Users of Excel-Lent software can easily navigate through the input screens to edit, analyze, and produce reports on optimum gear and gearbox design for various industrial and other applications.

Many gear uses

“This software is not designed for any specific industry,” continues Chinnusamy. It can be used for machine tools, heavy materials handling equipment, and even the wind-turbine industry. For the wind-turbine industry, designers need a full understanding of all the operating loads on the gear members to arrive at the required power rating.

Key calculations include the AGMA (American Gear Manufacturers Association) power rating and load calculations, including bending strength geometry factor (J) and pitting resistance geometry factors (I). Output from the software is a single page of data printed in a format that is easy to read and interpret. Other commercial software typically prints five or six pages of information, which may be confusing to most design engineers unless they are gear experts, Chinnusamy further observed.

The users of Excel-Lent need not be familiar with AGMA standards to use this software. Those who are not gear engineers can also benefit from the gear engineering knowledge embedded in the software package.

The software contains three sections: design, analysis, and gear dimensions. Any of the sections can be used individually to run calculations. On a typical job, according to Excel Gear, hundreds of hours typically spent doing the calculations can be saved.

A closer look at each section

DESIGN: This section calculates gears sizes based on minimal user input. The user must specify only the input rotational speed, gear ratio, power to be transmitted, and the material and heat treatments selected from material tables of commonly used materials in the industry.

Key values calculated are the diameter and face width of the pinion required for the surface-fatigue power rating and optimized DP or module (based on the calculated diameter) required for the bending fatigue power rating. The data are automatically exported to the analysis program. Results are the power ratings for 5,000 to 100,000 hours of B1 life (A reliability factor of 1).

When required, other values such as face width or center distance may be entered but Excel Gear recommends leaving the face width and center distance values blank for an optimized gear design. Design and analysis programs are used to design one gear stage in sequence on an external or internal spur and helical gear mesh.

ANALYSIS: This program calculates the power rating of a gear set for 5,000, 10,000, 25,000, 50,000 and 100,000 hours of B1 life, a reliability factor of 1. Reliability factors of 1, 1.25, or 1.5 can be selected as required. The user must input a mesh type (spur, helical, internal and external), pressure angle, helix angle (if applicable), pinion speed, number of teeth in pinion and gear, material (from the list provided in the software), face width, DP or module and quality required. Crown and/or profile shift, if used, can also be entered. The program calculates the power rating of the gear set and shows HP or KW capability along with torque, tangential force, and static capacity. Static capacity is based on yield strength and, if bending stress exceeds yield strength, permanent deformation or even tooth breakage may occur. If results are satisfactory, the user can print the single page results or, optionally, print all the AGMA factors used in making the calculations.

Most commercially available gear software will generate five or six pages of output along with required bending and surface fatigue strength of the gear set. Therefore, the user needs knowledge of metallurgy to select proper material and heat treatment or must consult a metallurgist.

By contrast, the Excel-Lent software program lists commonly used gear material for the user to select. When results are not as required, the user can select another material or change design criteria as required for needed results. If a special material is required, its yield, bending and contact stress numbers are easily entered. If any of the required input data are missing, the program prompts the user to supply the missing information. Metric or inch units are selected with just one click.

DIMENSIONS: In the opinion of the manufacturer, Excel-Lent gear dimension software is the most versatile program available. The program calculates manufacturing dimensions for a new pinion and gear, or calculates the dimension of a pinion or gear to mate with an existing pinion or gear. This can be done for external gears, internal gears, or a gear rack. Users need only to enter the type of mesh (spur or helical, internal, of external), pressure angle, helix angle (if helical gears), number of teeth in pinion and mating gear, DP or module and the quality of the gears.

The program then calculates the center distance, dimension over pins, span measurement, form diameter, roll angles and all gear tolerances to match the quality required (AGMA, DIN, or ISO). The program calculates the helix angle required to match a specified center distance when the user chooses that option.

The program displays plain English error messages when inputs are questionable or in error. For example, if the center distance is incorrect, the program will flash error messages such as, “Center distance specified is too large/small.”

The program calculates optimized profile shifts for a pinion and gear operating at a non-standard center distance, when the operating center distance is specified. If the profile shift required to operate is large and makes the top land narrow, the program will flash warning messages and display the proper profile shift amount to avoid narrow top land.

Excel-Lent software further provides users the option to balance beam strength or specific sliding of gear and pinion, if required. This is key for wind turbine gears. The program will also calculate gear blank tolerances to produce the required quality level, when shaft and bore diameters are entered.

For further information or a test demo, available on CD or onsite, contact:

Excel Gear Inc.
excelgear.com

Excel Gear Announces Two Key Appointments

Excel Gear, Inc. of Roscoe, Illinois announces the appointment of Denis Bermingham as the manager of manufacturing engineering and special projects, plus William “Bill” Powers as the company’s marketing manager. Both appointments were made by company president N.K. “Chinn” Chinnusamy, who noted these hirings were made as the result of the company’s recent growth and anticipated expansion into new market segments.

Denis Bermingham, new manufacturing manager

Bermingham brings a strong engineering background in metalworking and machine tool building to his new position, as well as an extensive knowledge of metallurgy and heat treatment. He will oversee Excel’s manufacturing engineering and special projects, as well as continue the company’s ongoing implementation of lean manufacturing strategies. Denis brings 30 years of manufacturing and machine tool experience to Excel Gear. He worked the majority of his career at Ingersoll Milling Machine in Rockford, IL in the Manufacturing Engineering, Assembly, Engineering, and Prototyping departments. He has a degree in Industrial Technology and will be responsible for the various manufacturing functions at Excel.

He notes, “I joined Excel Gear to become part of the technical/manufacturing environment here. We can offer customers innovative solutions, with excellent quality and value. I’m very excited to be part of this team.”

Bill Powers, new marketing manager

Powers brings 30 years’ experience in the gear and machine tool business to Excel. Formerly an account manager, project manager and supervisor of customer training with Ingersoll, as well as other metalworking/automation systems firms, he has handled various sales, marketing and customer relations functions, giving him a well-rounded perspective on the dynamics of the industry. He has a degree in Business Administration and will oversee all the marketing and business development for Excel.

Bill observes, “Chinn has structured a first-class company at Excel, supplying engineering-based products, brought to market by a very highly-skilled and dedicated team. All customers receive the highest quality possible, backed by service and application assistance that’s second to none. It’s a great working environment and I look forward to the challenges of our changing markets.”

Excel Gear, Inc.
www.excelgear.com

Automated gearbox testing builds in consistency

A gear manufacturer shows how it automated formerly time-consuming manual tests.

William L. Winterbauer, Ph.D.

Principal Engineer

QED Services

Ann Arbor, Mich.

The U.S. military has demanding requirements for the hardware it needs. Take, for instance, a set of gearboxes built by Excel Gear Inc., Roscoe, Ill,  for missile launchers on the U.S. Navy’s new DDG1000 series of ships. The gearboxes are drive elements for the servo systems that rotate and elevate the missile launcher. For good servo performance the boxes must meet the Navy’s requirements for stiffness, efficiency, and low backlash.

A prototype was tested using a time consuming manual method. Although satisfactory, the method required careful checking to prevent data entry errors. Requirements for the test system called for high accuracy, elimination of measurement errors, and elimination of data entry errors. The company’s experience automating the test procedures provides a useful design lesson.

After successfully completing the prototypes, Excel Gear president N.K. Chinnusamy, decided the production run needed improved assembly procedures and to automat the test methods. Preload on the bearings was identified as an important factor – too little preload allowed excessive backlash while too much decreases efficiency and generates heat. A measurement accurate enough to size an optimum preload spacer is difficult because before the spacer is in place, the bearing can tip from side to side.

The company manufactured a set of fixtures to prevent bearing tipping and improve the repeatability of the preloads. The fixtures also improved the efficiency of the first production boxes and reduced their backlash from what had been attained in the prototype boxes.

Types of tests

The units called for several tests. For example:

Temperature tests during run-in: The primary sources of heat in the gearbox are seal friction, bearing friction, and oil churning. The heat generated by oil churning distributes throughout the box and dissipates through the case. Seal and bearing friction are concentrated and, if excessive, will cause failure. Temperatures are checked near the bearings on the high-speed shaft, where measurements on the prototype boxes showed the highest temperatures. These areas were also near the seals. Although it isn’t possible to separate the heat generated by the bearings and seals, the seals seem to generate the most heat.

Temperatures were recorded for two hours with the box running at maximum speed. After cooling, the test was repeated with the box running in the opposite direction. In the test, temperatures rise rapidly at first and then at a decreasing rate. While the temperatures do not reach equilibrium, in operation the boxes will not run continuously for two hours, and they will reach top speed only intermittently.

Gear-train stiffness: This characteristic, measured with the output shaft locked, is the ratio of the input-shaft motion to the torque applied, in Nm/rad. Torque was applied using a hydraulic actuator with two opposed cylinders driving two racks against a pinion. The racks are held in the pinion by a bushing. This results in friction force opposite to the direction of motion. Because the friction in the hydraulic actuator would cause measurement inaccuracies, the torque is measured between the actuator and the input shaft using a Dataflex 42/1000 torque transducer. This sensor has a capacity of 1,000 Nm in either direction. Torque is determined by measuring the twist in the transducer shaft using rotary encoders in a differential circuit. An encoder rotor is mounted at each end of the shaft. Because the encoder read heads are mounted to the stationary part of the transducer, there are no slip rings. The A-quad-B output from the transducer is converted to a voltage by an encoder electronic box. The voltage output range is 0 to 10V with a no load value of 5V, and the calibration constant is 0.200 Nm/mV.

Rotary motion was measured using a 2,000 line rotary encoder (resolution of 0.018° ). Because the input shaft extends through the box, the encoder is mounted on the opposite end of the shaft from the hydraulic actuator. When the box is in operation, a brake is mounted on this end of the shaft.

The A-quad-B output from the encoder is converted to a voltage by the programmable encoder-control box. The range and number of volts per degree can be set depending on the amount of rotation to be measured. The output has a range of 0 to10V. For this test, the output was 8.100° per V and the no-rotation voltage was 5V.

Gear train backlash: Some backlash is necessary to provide running clearance for the gears. Too little backlash results in overheating and premature failure, and too much degrades servo performance. Backlash is determined from the data collected for gear train stiffness.

Breakaway torque: For these boxes, it was low and measured manually using a snap-torque wrench. Although automated tests are usually preferred, a few are so simple that the programming required is not justified. This test, for instance, was the only one not automated.

Gearbox power losses over the full range of speeds: Input torque was measured with the gearbox running at a set of speeds both clockwise and counterclockwise. The torque is a nearly linear function of speed with a small component of stiction. This is preferred in a servo system because it contributes to servo loop damping. Because the torque is nearly a linear function of speed, the power-loss curve is nearly parabolic.

Test equipment

Accompanying images show the test equipment and The test hardware table lists a few of its details. The software used, DASYlab, is a graphical programming language. It is programmed by placing block diagrams representing data collection operations on a screen and connecting them with “wires” to control data flow. In the system used here, processed data is written to disk in a tab-separated format suitable for further analysis using Microsoft Excel.

Programming the data collection: The DASYlab block diagram provides an example programming screen. Each block represents an operation on the data such as collecting, scaling, saving to disk, and displaying. This programming method is faster than writing code. For example, the voltage output from the torque transducer, encoder, and thermocouples was connected to the electronic interface box. This box has a built in reference junction for the thermocouples. The device also has digital and analog outputs but these were not used. The interface box scans its inputs and converts from analog to digital values. These are passed to the computer through a USB connection at about 1Hz. This is relatively slow for data acquisition, but more than adequate for these quasistatic tests.

In the DASYlab program, the first box is an input box that “talks” to the hardware and places the input values on its outputs in digital form. Typically this is a special module that works only with particular hardware. Most other boxes do not depend on the type of hardware in the system. The other boxes used are numerical displays, graphical displays, and output boxes to record the data on disk. These boxes have corresponding components on a display screen. This screen can be a virtual instrument, that is, it can look like instruments such as voltmeters, oscilloscopes, and chart recorders. For this test the program converts the inputs to engineering units and displays the values several ways. Digital displays show the current numerical values of inputs.

Another display, an XY-plot, shows rotation on the Y-axis and torque on the X-axis. This feedback gives a preview of results. It can save much time because if something is wrong, such as a broken wire or failed thermocouple, it quickly becomes apparent. The test can be stopped, the problem corrected, and the test resumed. A problem that goes undetected until the data is analyzed wastes the entire test period.

A disadvantage of DASYlab is that this program had to be written with the computer attached to the interface hardware. It would be a great advantage to write the program sitting in front of a desktop computer rather than working in the test area using a laptop.

Details of the analysis

Backlash and Compliance: One advantage of automated data collection is the larger amount of accurate information than can be manually collected in a reasonable period. The additional data gives a better picture of the equipment characteristics than would otherwise be possible. In Backlash and compliance, the red line simulates points collected when the torque was varied from zero to maximum, to minimum, and back to zero three times. (The data shown are not actual values but they are an accurate representation of the type of data collected.) The data showed good consistency and repeatability, which produces confidence in the results. For instance, the blue line shows the curve fitted to the backlash and compliance data. The length of the vertical line at zero-load is reported as backlash. The slope of the lines fitted to the observations is the stiffness. This is a conservative method for determining such values. The normal manual four-point test would have given both lower backlash and compliance numbers. The four-point test uses two torques that are just a little higher than breakaway torque in each direction and two torques that are a quarter to one half of the full load torque.

Converting from manual to automated testing: The first use of an automated system involves debugging because the test system, as well as the tested device, may have problems. An advantage to starting this system was that previous manually collected results were available for reference. Problems with the test system are seen quickly. For the first test, some manual measuring devices were used in parallel with the new test equipment. This either verified the results or showed problems. For example, an incorrect scaling factor was quickly detected and corrected. This illustrates one principle of successful testing: Check the calibration of the test equipment before running the tests.

About the author: William Winterbauer is principal engineer with QED Services and a consultant to Excel Gear Inc.