Automatic Checking

in machine building, a process of checking the dimensions of machine parts in which the work of the operator is entirely or partially replaced by the operation of mechanisms in measuring equipment. The purpose of automatic checking is the reduction of time spent on inspection and the elimination of subjectivity in evaluations of quality.

The main operations of automatic checking are loading the parts, placing them in the checking position, checking, and separation into satisfactory and rejected groups. According to the degree of automation, a distinction is made among automatic checking that is performed by automatic devices (fully automated), semiautomatic devices (one or more operations are performed automatically), or monitoring devices. Automatic checking may be used to measure one parameter and, either simultaneously or sequentially, to check several parameters of the same part. Active monitoring is sometimes classified as automatic checking.

Automatic checking is divided into two categories according to function (depending on the number of groups of parts after inspection). The first category includes inspection for which only one group of satisfactory parts is separated within the tolerance limits and the other parts (one or two groups) are rejected. The rejected parts are separated into those that can be corrected (for example, a shaft whose diameter is too great) and those that cannot (for example, a shaft whose diameter is too small). This kind of checking is usually done on automatic or semiautomatic devices that are intended primarily to check finished goods in place of an operator-inspector. The second category includes automatic checking that makes up several groups of satisfactory parts, which are then used for the selective assembly of machines. Automatic or semiautomatic systems are designed for this kind of checking; their basic purpose is to facilitate the technological process of manufacturing. Automatic checking in which the parts are only sorted into satisfactory and rejected groups is frequently called passive, in contrast to active monitoring, which produces a change in the operating conditions or determines the end point of the process.

Automatic checking of the second category is the most common, because it can simplify the fabrication of parts and reduce production costs. This is accomplished by making parts with wide tolerances and providing accurate matching during assembly by joining parts from corresponding dimensional groups. This method is typical of mass production, when the production of parts with close tolerances is economically unfeasible (for example, the production of bearings and tractors). The automatic checking of the first category is less widely used because it involves inspection of all the parts, which is frequently economically unfeasible and technically unjustified. However, it is effective in certain cases, such as a fluctuating technological process that cannot be regulated practically, so that a reject may occur at any time during fabrication.

Various inspection and measuring apparatus, selected according to technical requirements and the purpose of the articles to be inspected, is used for automatic checking. The economic effectiveness of the system depends on specific production conditions. With a stable and well-adjusted technological process, only sampling inspection of the parts is needed (over a given time or after production of a batch of parts). The use of active-monitoring apparatus and of measuring devices that can operate with computers that provide averaged indications of the state of the technological process during a certain time, as well as of measuring equipment that periodically checks its own accuracy and corrects itself, is most effective in automatic checking.