Patent GB-1507365-A (GB)
Title: Object location detector
IPC: G01B11/00
Filed: 1975-03-20
Abstract: 1507365 Elimination of spurious signals MULLARD Ltd 20 March 1975 11659/75 Heading G4R An object location apparatus for use on a conveyer belt system whereon are randomly positioned and oriented substantially two dimensional objects of predetermined shape, detects each object as to its position and orientation so that it may be mechanically picked up and placed elsewhere in a known position and standard orientation. The objects outline is detected at its extremities by applying two parallel pairs of notional tangents which may be orthogonally disposed and which bound a space enclosing the object and which intersect with the objects outline at four tangential points the relative positions of which are determined and from which are derived the orientation of the object with respect to the tangent directions, and the position of a reference point in the object with respect to the tangents, whereby a mechanical handling device positioned above the conveyer belt downstream of the detection device may be correctly positioned and oriented to pick-up each detected object as it passes thereunder. In Fig. 1, objects 1 are moved by translucent conveyer belt 2 past camera 7 which images slit 9 illuminated by lamp 8 on to line array 19, Fig. 2, of photodiodes 20 which array is orientated in a Y- direction transversely to the X-direction movement of the conveyer belt 2, the position of belt 2 and therefore the X co-ordinate of a point thereon is detected by incremental shaft position encoder 17 mounted on the shaft of conveyer belt pulley 16, the encoder emitting a pulse at each increment which pulse initiates a scan of the object in the Y-direction by diode array 19. Each photodiode 20 detects when a respective portion of the object to be detected obscures the light passing up through belt 2. Four points on the object are detected a follows: The First Point (X 0 , Y 0 ) is detected when the first photo detector 20 detects a portion of the object; The Distant Point (X 1 , Y 1 ) is detected as being the point, over the complete scan of the object, detected by the diode 20 furthermost from the end 24 of the array 19, each diode along the array being counted as one Y direction increment; the Near Point (X 2 , Y 2 ) is detected as the object point detected by the nearest diode to end 24 (In each case a subsequent point lying on the notional tangent passing through, e.g. the Near Point, is ignored by the processing equipment); the Last Point (X 3 , Y 3 ) is taken to be the last point of the object detected by diode array 19. Notional tangents 22, 26 and 27, 29 are shown in Fig. 2 constructed in the Y and X directions respectively. The output signal from camera 7 is a serial digital pulse train of the sequential scans of the object, obtained by sequentially sampling the diodes of the array at each position in the X-direction, each pulse transmitted corresponding to the detection of a portion of the object at its respective coordinate position by a particular diode 20. A notional reference point (X r , Y r ) and an associated reference direction making an angle # to the Y-direction, Fig. 2, may then be constructed so that gripping hand 5 may be moved to the correct position corresponding to (X r , Y r ) and its jaws 14 and 15 rotationally orientated to a position corresponding to angle #, Fig. 2, so as to pick-up the object 1. The four tangent points are calculated by digital processing circuitry (Figs. 3, 7 and 8, not shown) which is provided with a digital computer or microprocessor (not shown). Reference is made to a precalculated table of sets of values of tangent point co-ordinates each set being associated with the relevant value of # and (X r , Y r ). The set of values of co-ordinates most closely fitting the measured values is selected and the values of # and (X r , Y r ) are supplied to pick up device 5 for successful pick-up when the object reaches the pick-up area later. In order to identify and remove signals produced by foreign bodies on, and variations in translucence in, the conveyer belt 2, the circuit of Fig. 6 is connected in series between the camera and the digital processing circuit (not shown). A set of nine columns of shift registers 41 to 48 are connected in series and each has the same total of stages as there are photodiodes in the camera. As shown, by example in Fig. 6, nine shift registers 42, 44 ... 58 are arranged in columns and store, for each completed scan the diode output signals for that scan in register 42 and the signals from the eight previous scans in the subsequent registers 44, 46 ... 58 contain an array of binary picture elements representing a portion of the object. A pre-selected number of stages in the array corresponding to a ring of diameter nine picture elements are connected as twenty inputs of OR gate 59 the output of which is fed via an inverter stage 60 to AND gate 61 the other input 63 of which is clocked in an interleaved fashion with the shift register clock pulses. Output 62 of AND gate 61 is fed to those stages within the said ring whereby a zero on all the stages of the ring corresponding a "white ring" results in the clearing of all the AND gate connected stages within the ring and cancellation of any objects small enough to fit within the ring. The signals are fed via output 64 to the digital processor.