Automation & Assembly Solutions
Rotary indexing table use is widespread in automated assembly machinery and selecting the proper mechanism is essential for both maximizing performance and minimizing the cost of this critical component. This how-toguide will explore two common devices that can be used for rotary indexing and give advice for proper selection. These two popular devices are cam indexing drives and servo rotary tables.
Cam indexers are a ubiquitous mechanism that have been used for rotary tables for many decades. They are a great fit for applications that will always index the same angle and that require high-precision positioning at a very reasonable cost.
A cam indexer uses a mechanical cam to provide the motion control to position the load. A mathematical motion curve is machined onto the cam that provides extremely smooth and repeatable motion.
A cam indexer has two main modes of operation. One mode is referred to as “Cycle-on-Demand”. This indicates that the camshaft will be cycled one revolution at a time to advance the output one position at a time. This is typically achieved by using an inexpensive camshaft sensor package to detect camshaft position and a VFD to stop and start the motor. The camshaft dwell period offers a wide window for the camshaft to stop without affecting the position of the output. To cycle the indexer, a PLC gives a command to the VFD to accelerate the drive motor to a preset speed, the cam rotates one revolution indexing the output, a sensor sends an in-position signal to the PLC, and the PLC signals the VFD to stop the camshaft during the cam dwell position. The table will be in the dwell position for however long is necessary to complete the work at each station. The dwell time can range from a fraction of a second to several minutes or hours depending on the application. This combination allows very accurate positioning with an inexpensive drive system.
A cam indexer can also be run in a more traditional “Continuous” mode where the camshaft spins at a constant speed and the indexing and dwell time is controlled solely by the cam motion profile. Continuous mode is useful when other equipment will be mechanically synchronized with the camshaft timing or when the indexer needs to run at cycle rates faster than a motor can be stopped and started. A continuous indexer can run at rates in excess of 1,000 cpm. The limitation of continuous mode is that it may be impossible to machine a cam that requires a quick indexing motion followed by a long dwell time.
A fully programmable servo rotary table is another common option. There are two specific cases where a servo rotary table is advantageous. The first is when a flexible motion pattern is required. An example is two different products being run on one machine that each require different indexing patterns. The other situation that suits a servo indexer is when extremely fast positioning is required followed by a long dwell period. A cycle-on-demand cam indexer is limited by the need to accelerate the camshaft up to speed during the dwell period 
before output motion is started. There are practical limitations to how fast the camshaft can be accelerated so there will be a delay before motion is started. With a servo rotary table, the output rotates as soon as the servomotor starts moving. A practical example would be a load being indexed 90 degrees in 0.25 seconds. This is not difficult for a continuous cam indexer or a zero-backlash servo indexer, but a cycle-on-demand cam indexer may struggle with that motion. For quick servo indexing applications, a preloaded gear reducer with zero-backlash is critical to achieving smooth indexing motions with minimal settling time. A zero-backlash RollerDrive mechanism would be an optimal choice to achieve accurate positioning with great dynamic response.
For either style of indexer, application information including moment of inertia, indexing angle, indexing time, and dwell time is required. A reputable manufacture should then be able to properly size the rotary table for the application.
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As industrial demand for reduced overhead costs and increased efficiency grows, so too does the demand for manufacturing process and factory automation. Factory automation helps manufacturers to increase production rates, material efficiency, worker safety, flexibility, and more, all while bringing down overall costs.For almost any industrial process, conveyors are one of the most crucial components of a comprehensive factory automation system. mk North America is a leader in industrial automation, providing modular pallet conveyor systems, belt conveyors, sanitary conveyors, and more including custom conveyor design to meet specific demands.
Among mk’s most popular products, VersaMove conveyors are modular pallet conveyor systems that come in three configurations: the VersaMove Standard, VersaMove Plus, and VersaMove Ultra.Highly versatile and useful for a variety of industrial applications, VersaMove pallet transfer systems are ideal for factory automation. The SRF-P 1010 and ZRF-P1010, under the Standard configuration, are respectively well-suited for accumulation and indexing applications, each with pallet loads of up to 80 lbs. The VersaMove Ultra’s SRF-P 2012, meanwhile, is designed for the creation of heavy-duty systems capable of carrying as much as 700 lbs. per pallet.Combined with conveyor system modules like pallet lift and locates, lift and rotates, and right angle pallet transfers, these pallet transfer systems are capable of a variety of factory automation tasks as diverse as quality control, building automation, general material handling, and more.
Flat belt, cleated belt, modular plastic belt, and other conveyors made with mk aluminum t-slot extrusion create even more possibilities for modern factory automation. The MBF-P 2040.02 is a modular plastic belt conveyor designed for applications involving heavy material handling such as general manufacturing, as well as those requiring contact with high temperatures. Special conveying applications requiring positioning or loading of products are well-served by the ZRF-P 2040.02, an attachment timing belt conveyor designed for indexing applications.
