# Impact of a Robot Manipulation on the Dimensional Measurements in an SPC-Based Robot Cell
## 1 Introduction  
Recently, there has been an increasing emphasis on product-quality and process control in the process industry. Due to the increasing daily demands for better product quality, the need for ever-improving measuring systems is also on the increase. Several different approaches are used to ensure adequate quality and process control. The most commonly used method in manufacturing is Statistical Process Control (SPC) [1, 2]. Amongst SPC techniques (histograms, control charts, scatter diagrams, etc. ), there are methods for evaluating the manufacturing process's capability (including the capabilities of the measuring system). Coordinate measuring machines (CMMs) have a leading role in manufacturing metrology because of their versatile and flexible use. However, in addition to these good qualities, they also possess some important disadvantages. They are costly, in many cases, time-consuming, and they require temperature-controlled rooms to achieve their optimum measurement capabilities. Many potential sources are able to influence CMMs' measurement uncertainties, most notably the environment of the measurements, the measurement procedure [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15], the measuring equipment [3, 9, 10, 11, 14, 15], and the operator [3, 4]. The operator influences process measurements through conscious or unconscious actions. Using different measuring tools, the operator can apply forces of different sizes (e.g., measuring lengths or diameters when using calipers). When holding the object in clamps for measurements with a CMM, the operator can cause deformations of themeasured object or introduce uncertainty due to a positioning error. Unlike operators (in general, humans), industrial robots have much better repeatability and accuracy of their movements. Besides, they can operate continuously without stopping. In this regard, robots can be used in place of operators and increase the data's reliability, and, at the expense of continuous operation, the sample of measured objects can be increased. These days, robots also allow for a reasonable degree of flexibility. Numerous studies have been conducted to speed up the measurements involving industrial robots, laser scanners, and optical CMMs [17; 18; 19; 20]. [PERSON] et al. [17; 18] and [PERSON] [19] compared CMMs with laser scanners attached to industrial robots in the automobile industry. In all cases, the measurement cycle time was significantly reduced compared to CMM measurements. Additionally, the density of measured points was increased. However, it should be noted that it was not possible to measure all the characteristics using the combination of a robot and a laser scanner, and the method is suitable for measuring relatively large subjects (e.g., car chassis) with a tolerance of 3 mm (\(\pm\)1.5 mm). [PERSON] et al. [20] used an industrial robot to manipulate a measured object inside the CMM's working area. The main goal of the research was to perform the re-positioning of a measured object with a 5-axis industrial robot and fully automate the measurement cycle. They concluded that it is possible to conduct measurements using a CMM-robot system. However, the measurement results are dictated by the measurement uncertainty of the least-accurate component of the system, an industrial robot in this case. Measurement uncertainty that encompasses the operator's influence can be significantly reduced by changing the measurement methods appropriately. The operator's influence includes the determination of the measurement probes and stylus [12], the sampling method [6; 7; 8; 13] for the measured features (distribution and number of points), and the positioning of the part and fitting algorithms [9; 10; 11]. As demonstrated in Reference [20], with some additional improvements, the uncertainty part due to the positioning error can be reduced. Nevertheless, [PERSON] et al. [21], [PERSON] et al. [14], and [PERSON] et al.