A Crash Course On Precision Rotary Tables

Posted on Sep 15, 2020

precision rotary table

Rotary tables in the world of manufacturing are used for precision metal processing. They are usually made of a sturdy base that can be fixed to another fixture. The rotary table is essentially a disk that can spin naturally or via a worm wheel. Precision rotary tables have numerous uses in the industrial industry, including machining, inspection but also welding.

What Is a Precision Rotary Table?

Precision rotary tables are used in many industries, from fixing large weldments in aerospace, to positioning containers for label applications in consumer product manufacturing, to positioning medical product components for assembly processes. You can find one almost anywhere in the manufacturing industry. In this article we will give you an overview of the rotary table.

:: Read more : How Can a rotary table indexer Help?

Basic Specifications 

Let us first talk about some of the most important specs when it comes to precision rotary tables. The table diameter refers to the surface area of the rotating table, and the through hole diameter is the width of the center hole of the workstation. In this way, we have the maximum axial load, which is the maximum weight that the rotary table can bear when the table is pushed to the working surface along its vertical or horizontal axis. Finally, the maximum radial load is the maximum weight that the rotating table can bear during concentric operation. The design of the rotary table can reach the maximum rotary table speed set by the manufacturer. The minimum index increment is the minimum angle setting on the rotary table.

Selection Factors

There are some important factors to consider when choosing a precision rotary table. In principle, it seems simpler to rotate the part and stop periodically at a precise angle. However, in reality, designing and manufacturing machines that will accomplish this task accurately and reliably within the expected life of modern manufacturing machinery will become a very difficult challenge. The primary factor of rotating mass is to determine the mass moment of inertia. This is usually ignored when choosing a rotating device for an application. Once the moment of inertia is known, the size of the rotary indexing table can be correctly determined for any speed that needs to be reached. 

Another important aspect is the size and weight of the object to be moved. Size is an obvious limitation because you need a rotary table large enough to place the required parts. In order for the rotary indexing table to work effectively without causing internal damage, it needs to be accelerated and decelerated at an appropriate speed. 

Finally, other important factors are accuracy and precision. There are some applications, such as rotating large parts to allow welding features on them, where each stop position may be quite loose, such as within a quarter of an inch; while in other applications, it needs to be repositionable in the thousands within inches.

Mounting Types

The installation method of the precision rotary table can be horizontal, vertical or inverted. When installed horizontally, the workbench surface is in a flat, vertical and horizontal position. When installed vertically, a rotary table is installed so that the surface of the rotary table can run up and down. In the reverse layout, the rotary table can be rotated upside down in a horizontal position. The location of the drive of the rotary table can depend on the mount. The drive can be placed on the back, below, on the top or on the side. 

When mounted horizontally, the spinning table top drive is positioned above the table floor. When the rotary table is horizontally placed, the side-mounted drive is located on the edge of the table board. The driving mechanism of the rotary table may be manual, electrical, pneumatic, hydraulic or non-driven. For manual revolving workbenches, release the workbenches and manually spin the workbenches with the crank.

What Affects the Precision of a Rotary Table?

When determining the influencing factors on the accuracy of the rotating table, the first thing to look at is the mechanical properties of the table itself. A rotary table contains six degrees of freedom. Each of these movements increases the total amount of positioning error in the rotary table. Usually, a rotary table is driven by a worm gear, which is connected to the motor through a rotary encoder on the back. The position of the table can be determined by the number of pulses transmitted from the encoder to the control device. The four main sources of error due to the semi-closed position loop are geometric errors, thermal deformation, elasticity and wear. The sum of these errors is called angular positioning error. In order to greatly reduce the angular positioning error, the ideal position for installing the angle encoder is on the rotating shaft under test. The angle encoder is installed under the rotary table, and the rotary encoder is installed under the rear motor, the position loop is now considered a closed loop system.

Precision and Backlash Considerations

Precision is a relative term. About a quarter of an inch is great and will meet the accuracy of its application. Others, for example, require micron-level accuracy in measuring and indexing devices. Then, there are some applications that fall within these extreme ranges. 

The misunderstanding is that you may have used an inaccurate indexing device and made it accurate by introducing a pin or wedge locking device. These devices increase the complexity and cycle time of use, and when they are used together with a high-precision indexing machine, they may cause damage and reduce accuracy.

In the actual test, by selecting specific components, motion index drive, servo rotary indexer, the measured accuracy is as high as 5-6 microns. These are not the results approved by Motion Index Drives, but the results of customer certification. When starting and stopping large amounts of data, it is important to know how fast it takes to stop the application with large amounts of data. 

In a less rigid environment or in the presence of higher recoil, faster start and stop will bring many control problems. When moving masses (whether rotating mass or linear mass), starting and stopping in a system with a backlash of several arc minutes will cause a lot of back and forth movement in the gear system. The result is a force that is difficult or even impossible to calculate. In addition, when the gear head is used in rotating applications, the farther the mass is from the center of rotation, the greater the backlash. In applications with very slow deceleration times, recoil may not be a problem.

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