The gear is one of the most widely used manufacturing parts in the world. The number of real-world applications of gears is nearly limitless: from time keeping, to automotive, to medical and aerospace, to helping humans gain a mechanical advantage in labor. As a result, there is hardly an industry that doesn’t use gears in some capacity, whether it be in their manufacturing process, in their finished products, or both. Because of this wide array of applications, gears themselves come in a wide range of sizes and types. Spur, spline, bevel, and timing are just a few examples, and within these categories there are many unique features such as tooth count, size, and face width. All of these options can also come in a broad range of materials and finishes. As a result, the need to have quality control (QC) processes that are accurate, flexible, reliable, and fast are crucial to keeping production on schedule.
Inspection with Precision Tools
There are a number of gear-inspection methods that have been available for many years. When measuring over pins with a micrometer, the appropriate size pins for a selected gear are placed within the width of space between teeth on opposing sides of the gear. A micrometer is then used to take measurements over the pins and compared to a theoretical dimensional value for features such as tooth thickness.
Gear tooth inspection Vernier calipers are devices with sliders that can be used to measure features such as tooth depth, tooth height, and addendum height with a combination of scales on the device that are line-based, with each line corresponding to a certain value. Handheld or tabletop gear testers, on the other hand, are devices where a sample gear from production is placed into a device mating it to a master gear for testing. The sample and the master are then run through rotation and runout on the gear and can be measured via a dial gauge on the system.
While these are all affordable, time-tested options, it is important to factor in the following considerations: When using a micrometer over pins, the user must have the appropriate pin sizes for all of the gears in production. Gears with an odd number of teeth will also require additional calculation to account for being offset from center. When using tools such as Vernier calipers, there is a certain amount of time and training required to learn how to properly use the scales and read them in order to obtain accurate results. With the gear tester, on the other hand, issues such as master gear wear over time become a factor. With all of these tools, the issue of time also becomes a factor. These methods require measurements to be taken piece-by-piece manually, which can slow down a busy QC department. On top of this, when making hand measurements, the opportunity for human error is introduced, especially if there are multiple individuals in a given QC department taking readings.
Merits of Vision Systems
Due to faster measurement, increased throughput, and greater accuracy by removing operator subjectivity, the latest metrology inspection systems offer more efficient gear inspection, especially on a production level. A vision system, which is essentially an upgrade to the traditional optical comparator, uses high-definition video cameras with customizable lighting rather than using lenses and mirrors, to create an image on a touchscreen PC monitor. This advancement enables a feature called video edge detection (VED), which automatically detects the difference between light and dark, eliminating the human error usually seen in operator-to-operator subjectivity. Customizable lighting can also be adjusted in real time, depending on the surface finish of a gear, to ensure the image is not washed out or distorted.
An advanced vision system is combined with equally capable software. Systems such as the Starrett AVR-FOV benchtop vision system have integrated software to make the inspection process intuitive and user friendly. CAD files can be imported as DXF files to instantly compare a feature such as gear tooth thickness or slot width to a master overlay for quick checks. Optional touch probe capability also provides CMM (coordinate measurement machine) functionality by allowing data points to be taken from discreet, hard-to-reach areas including bore holes that might also be a precision feature on a given gear. A touchscreen monitor allows the user to simply touch features of the part to record desired features such as points, lines, arcs, angles, and more. Once the desired features are collected, they can be compiled into a part program that can be stored for future use. Variable lighting control can also be built in as programmable steps.
Ease of use
At this point, a user can walk up, place a gear or multiple gears in the view of the camera and initiate the program. In a few seconds, accurate and dependable results can be obtained time and time again regardless of who is using the system or their level of experience. This feature virtually eliminates error due to user-to-user subjectivity.
As production demands increase, lead times need to be decreased without compromising quality. The ability to confidently perform everything ranging from quick checks to in-depth QC inspections in seconds has never been more important. The Starrett AVR-FOV allows for multiple small gears, or more features of a larger gear, to be placed in the field of view. When combined with Super Image technology, where a master image of the entire stage is created from multiple smaller images, entire batches of gears can be inspected simultaneously.
This process is scalable as well. Starrett vision systems come in a variety of sizes — from small, benchtop inspection microscopes to benchtop vision systems, to floor standing systems with large stages, all capable of being equipped with multiple lenses. Once the results are obtained and presented to the user as a report, they can be instantly saved and exported in a number of different formats, depending on the application requirements.
When it comes to inspecting the numerous features of a gear, there are many paths to success and all of them have their merits. In a modern manufacturing world, however, where speed and accuracy are paramount, the speed, accuracy, and ease-of-use of a vision system is invaluable.
