Romer arm

A measuring arm is a portable, manually operated instrument with which the geometry of a component can be measured. Unlike a coordinate measuring a measuring arm has no linear material measures but the location of the button at the top of the measuring arm is taken with incremental measuring systems in his joints. Measuring arms can be used directly in the production area and do not need a temperature-controlled environment. Compared with CMMs, the achievable accuracy is, however, smaller by an order of magnitude in about.

History

Measuring arms were developed in the late 1970s. They were looking for an instrument with which the geometry of large workpieces could be measured without having to bring the workpiece to the meter. The original design described by the inventor Homer Eaton in 1974 in the U.S. Patent no 3,944,798. At the time of the invention Eaton measuring arm was designed exclusively for the measurement of angles on curved pipes. In the 1980s, Eaton graduated with Romain Graiger together, founded the company and developed Romer measuring arms for general industrial applications of production metrology.

Design and function

A measuring arm is similar to a human arm extended ( with upper, lower arm and hand) of two arm parts and the sensor head. Each arm portion, and the sensor head are connected to each other by two joints. Thus, the arms do not bend, which would lead to a larger measurement uncertainty according to the arms are designed for high rigidity. They usually consist of a tube made ​​of fiber reinforced plastic. By the six joints of the sensor head can be rotated at any point in three dimensional space, and the sensor in three spatial angles ( for a total of six degrees of freedom).

A sensor head may be either a tactile switch or an optical sensor such as a laser light section sensor is used.

With a measuring arm many individual points are added (when using a tactile probe ) or large point clouds (when using a light section sensor ). This geometric elements are first calculated (eg circle, plane, cylinder ) from which, in turn, derived to be measured characteristics ( dimensional tolerances such as the diameter or shape and position tolerances such as flatness or cylindricity ) and checked for compliance with the tolerance. For this processing, the measuring points of the same software used in the control, which is also used for coordinate measuring machines.

Accuracy

Through the six series-connected joints, the plant uncertainties in the rotation angle measurement of each encoder to its nearest neighbors continuously. Is different with traditional coordinate measuring machines, as these linear incremental encoders are aligned in three mutually orthogonal directions in space and errors in each linear transducer system is not transferred to the other axes. For this reason, measuring arms are less accurate than coordinate measuring machines with a similarly large measurement volume. The uncertainty in the probing of a point is measuring arms usually at several tens of micrometers whereas coordinate measuring machines can achieve an uncertainty of a few micrometers.

Area of ​​application

Measuring arms are " spread over a wide range of waste land ". The automotive industry, " poses with her high quality requirements of customers is the greatest " .. According to the " golden rule of Feinmesstechnik " should be only one-tenth to one-fifth of tolerance, the measurement uncertainty. Therefore, measuring arms are only suitable for the measurement of characteristics, the tolerances in the region of a few tenths up to be several millimeters. Examples of the use of measuring arms are found in " measurements inside the vehicle ," the " very limited with a stationary measurement system are possible." "This can be measured, for example, the complete panel, the pedals or rear center of the vehicle and located in the vehicle mounting brackets. " Other examples are

• The measurement of castings, rough fits and gap dimensions
• Reverse engineering