Theoretical applied questions and their implementation in development of hierarchical computer control systems ( CNC ) of facsimile copy machines for art engraving on minerals

The technological scheme implementing machine engraving on a mineral and facsimile transfer of the halftone image from the personal computer is offered. The dot (microstroke) image is formed by a pulse system together with an electromechanical converter, such that the integral optical density of separate fragments equals optical density of the same fragments of the initial image. Structural construction and separate parameters of a two-level hierarchical control system are formalized. The description of the top level of the developed hierarchical control system is given. Facsimile copy machines controlled by CNC systems, are a branch of digitally controlled machines, and belong to a class of mechanotronic systems. The raster approach to creation of halftone image on the surface of the polished mineral by slotting is described below. Proportional electromechanical converter with a chisel is used for that purpose. The control system of the machine is a two level system, based on main hierarchical principles. The top level is implemented on the personal computer. Image is entered in the computer as a videosignal, quantized in time, or as a scanned image. This signal is stored as a bitmap (pixel array) and can be considered a lattice function of two arguments. The interpolated values obtained in continuous space, which is defined by the trajectory of the chisel, are submitted in fragments via communication channel to the lower level, implemented on a programmable controller (PC). PC is a base of a digital cyclic open impulse system. The implemented technological process of machine engraving on a mineral produces facsimile transferring of a halftone image from personal computer. The impulse system together with the proportional electromechanical converter creates dot or microstroke image, in which integral optical density of separate fragments equals the optical density of the same fragments of the initial image [1]. The impacts on the surface of the material are created by the proportional electromechanical converter, in which the electromagnetic energy creates force F, which is proportional to a signal Ujvideo.. The force F is applied to an anchor with a chisel and forces it to move, thus creating kinetic energy. The complexity of implementation of facsimile transferring of the flat image on a plane with exact reproduction of all grades of optical density forces to use dithering, which is a 2-dimensional kind of impulse modulation, where the 2-dimensional spectrum of a continuous signal is replaced by a sampled image and, correspondingly, its spectrum, which is possible without deterioration of visual perception based on Nyquist theorem. To produce it, scanning moves of a chisel parallel to the surface of the blank are used to create dots or microstrokes, and the size of the dots is defined by the moves in normal plane (raster moves) [2]. In reproduction systems the human vision acts as a lowpass filter, creating continuous signal from the impulse train. It experimentally shown that the vision system perception of reference periodic images with different spatial frequency decreases monotonously and at some boundary frequency the eye does not recognize discrete structure. This characteristic was offered by Ju.S.Andreev and described as a frequency response of the vision analyzer , (1) ) 343 . 0 exp( ) ( v v W − = where v – spatial frequency [mm] The available array of pixels is recalculated to obtain required image size with respect to the physical image size and drive step. From the grayscale image, which is quantised by level, frequency and amplitude of the chisel moves are defined, such that they result in the same optical density D. The quality of the obtained image depends on the quality of the initial image, which can be described by the following parameters: 1 V.I. Morozov, I.N. Mikov, S.V. Fedorov, MGGU, MGGU, Bauman MSTU (Receiwed, revised version received August 2, 2002)