An indexing table, better known as the rotary indexing table, is an integrated motion system where repeated angular displacement is followed by motionless dwell during a machine cycle. A rotary indexing table is designed to create repetitive moves around a platform. Simply put, indexing tables are highly precision positioning devices which index parts to be machined in a series of operations.
Rotary indexing tables are typically composed of mechanically powered transmission devices along with motors, sensors, encoders and controllers. For servo tables or cam drives, electric motors (or servo motors) are usually employed. Indexing tables come with affordable cost and can only index to set angles, but are able to position work precisely.
Rotary indexing tables move and position components during manufacturing processes. Items to be machined are rotated to a set position, either fixed or variable, by one of these indexing units.
The indexing tables are typically used to position objects at specific points surrounding a workspace so that they can be machined. Think of it like an assembly line, but circular. Each of these objects is moved at a precise distance by the table, where the operation (vision or physical) is carried out. The indexing tables are also able to accommodate certain assembly functions depending on your specific requirement.
Some of the essential parameters on which a rotary indexing table is based include the required resolution of the application (or the smallest increment to measure or move), the needed repeatability and accuracy, and other mechanical variables such as the feasible levels of backlash or hysteresis. Another core parameter is the loading, which includes axial, radial, torque and moment loads, all of which can affect the type and size of the indexing table used in the designated application.
There are many applications in which a rotary indexing table can be used, including primarily manufacturing, inspection and assembly tasks. For example, machining, assembly and bottling machines all make use of the indexing tables. Generally, during the process, a work piece or group of small parts are grabbed from the work areas and then moved to the work stations where sequential machining and assembly tasks take place. With that said, industries that are benefited from the adoption of rotary indexing machines including aerospace industry, automotive industry, medicine, science, food and beverage industries and many others.
In this section, we’ll review some of the key factors that will help you choose the best indexing table for your designated application:
● Accuracy: You need to determine how important accuracy is for your application. Many tend to falsely assume that you can take an inaccurate indexing table and use a shot pin or wedge lock device to make it accurate. These devices actually increase the cycle time and complexity, which may also cause damage to the indexing device, thereby making it less accurate.
● Backlash: You also need to know how fast you need to stop your application mass. In an environment where increased backlash exists, faster starts and stops will often lead to control issues. This results in the presence of a force that may become impossible to calculate. Moreover, when gear heads are utilized for a rotational application, the further away the mass is from the center of the rotation, the more backlash is magnified. But in applications wherein decelerations times are exceptionally slow, the backlash may not pose such a big problem.
● Mass moment of inertia: This is a very important factor when it comes to rotating masses. This is an often overlooked factor when choosing the proper indexing device. Knowing your mass moment of inertia should in fact be the first and foremost determinant because once it is known, a rotary indexing device can be sized properly for any speeds that need to be achieved. The most common mistakes that many buyers make is having the false conception that rotating a mass is no different from pushing a mass. They more often than not calculate the required torque to move a certain weight, which is very likely to lead to failure.
● Environment: Environment can be a factor that causes failure to the integration of a rotary index table. For instance, in the food manufacturing industry, wash-down chemicals can cause corrosion to metal components of the indexing device. That is why sometimes indexing units are required to be made of stainless steel components for the specific application to prevent damage due to corrosion.
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