Scanning of workpieces such as lumber cants

A method of obtaining information about a workpiece with the use of an array comprising a plurality of adjacent photoresponsive detector elements that have respective optical axes which lie in a common plane, each of said elements having a response field limited to small angles of divergence from its optical axis and producing an output having a magnitude corresponding to the intensity of radiation that it detects in its response field, wherein said array is caused to scan across a workpiece in a direction substantially normal to said plane and at an ascertainable velocity while a pair of radiation sources that are spaced to opposite sides of said plane emit radiation towards the workpiece to be reflected from it for detection by elements of the array, said method being characterized by:

• A. during the time that a workpiece is being scanned, issuing a cycle signal at each of a succession of regular time periods so that each pair of successive cycle signals defines a measurement cycle;
• B. during each measurement cycle, exposing each detector element that has the workpiece within its response field to radiation originating from each in turn of said radiation sources, substantially to the exclusion of radiation originating from the other, the sequence of such exposures being the same for every measurement cycle and each such exposure occurring during a predetermined interval in the measurement cycle, to thus cause the detector element to produce a pair of discrete measurement outputs, one for each exposure;
• and
• C. so controlling the frequency of said cycle signals and the timing of said intervals in relation to the velocity of scan that
• (1) there is a substantial overlap between areas on the workpiece that are within the response field of a detector element during said intervals in each measurement cycle, which overlap defines a local area on the workpiece, and
• (2) the local areas for successive measurement cycles are in proximity to one another.

A method of obtaining information about variations in thickness of a workpiece as measured between substantially opposite surfaces thereon and in one direction along one of said surfaces by scanning said one surface in said direction by means of an array comprising a plurality of adjacent photoresponsive detector elements that have respective optical axes which lie in a common plane that is substantially normal to said direction, each of said elements having a response field limited to small angles of divergence from its optical axis and producing an output in response to radiation that it detects in its response field, said method being characterized by:

• A. during scanning, issuing a position pulse each time the scan advances through a predetermined distance;
• and
• B. causing a narrow beam of radiation to be emitted in a direction such that the beam
• (1) is substantially contained in said plane and
• (2) is at an oblique angle to said surface, so that the beam is reflected from said surface as a small spot of radiation that is detected by one of said detector elements, the particular detector element which, during any interval between position pulses, produces an output in response to such detection being a function of the local thickness of the workpiece at the location of the scan during that interval.

A method of obtaining information about a workpiece with the use of an array comprising a plurality of adjacent photoresponsive detector elements that have respective optical axes which lie in a common plane, each of said elements having a response field limited to small angles of divergence from its optical axis and producing an output having a magnitude corresponding to the intensity of radiation that it detects in its response field, wherein said array is caused to scan a workpiece in a direction substantially normal to said plane and at an ascertainable velocity while a pair of radiation sources that are spaced to opposite sides of said plane emit radiation towards the workpiece to be reflected from it for detection by elements of the array, said method being characterized by:

• A. during the time that a workpiece is being scanned, issuing a cycle timing signal at each of a succession of regular measurement cycle periods which are of such short duration that a local area on the workpiece is within the response field of a detector element during the whole of a measurement cycle period;
• B. during each measurement cycle period exposing each detector element that has the workpiece within its response field successively to
• (1) radiation originating from one of said radiation sources substantially to the exclusion of radiation originating from the other, to cause the element to issue a first measurement output having a magnitude dependent upon the intensity of reflected radiation from said one source,
• (2) radiation originating from said other radiation source substantially to the exclusion of radiation originating from said one source, to cause the element to issue a second measurement output having a magnitude depending upon the intensity of reflected radiation from said other source, and
• (3) a substantially lower level of radiation than that which gives rise to issuance of said measurement outputs, to cause the element to issue a reference output having a substantially low magnitude;
• and
• C. for each of at least certain of said detector elements, subtracting the magnitude of the reference output issued by the element during each measurement cycle period from the magnitude of each of its first and second measurement outputs issued during the same measurement cycle period, to produce first and second difference values, respectively, that are directly comparable with one another and with difference values that originate from others of said certain detector elements.

Apparatus for obtaining information about a workpiece at a measuring zone, said apparatus being of the type comprising a photoresponsive detector element that has an optical axis extending through said measuring zone and has a response field limited to small angles of divergence from said optical axis, said element being adapted to produce an output that has a magnitude corresponding to the intensity of radiation that it detects in its response field, and a pair of radiation sources that are spaced in opposite directions from said axis, said radiation sources being arranged to emit radiation towards said measuring zone for reflection from a workpiece in said zone to the element, said apparatus being characterized by:

• A. means for exposing the detector element, successively and briefly, during each of a regular succession of cycles,
• (1) to a level of radiation substantially lower than that originating from said sources, to cause the element to produce an R output, and
• (2) to radiation reflected from a workpiece and originating from each of said radiation sources substantially to the exclusion of the other, to cause the element to produce an A output and a B output;
• B. comparison means connected with said detector element and comprising a short term memory;
• C. means for transferring each in turn of the A, B and R outputs obtained during a cycle to said comparison device, for subtraction from said A and B outputs of the R output for the cycle, to produce .DELTA.A and .DELTA.B difference signals, respectively, for the cycle;
• and
• D. means for so controlling relative movement between a workpiece at the measuring zone and said detector element that the A and B signals for a cycle are produced in response to reflections from surface areas of the workpiece that substantially overlap one another in a local area, so that the inclination of the local area on the workpiece can be determined from the .DELTA.A and .DELTA.B signals for that local area.

A method of obtaining information about the geometry of a workpiece by scanning it with an array comprising a plurality of photoresponsive detector elements that have respective optical axes, each of said detector elements having a response field limited to small angles of divergence from its optical axis and producing an output in response to radiation that it detects in its response field, the response fields of the detector elements being arranged in a substantially regular pattern, the workpiece being so disposed during scanning that it has a substantially large surface facing towards said array and intersected by said optical axes, and the workpiece being illuminated for scanning by radiation from a pair of radiation sources which are spaced in substantially opposite directions from the workpiece and the array and which emit radiation towards said surface at opposite angles that are substantially oblique both to said surface and to said optical axes, said method being characterized by:

• so controlling
• (1) relative movement between said array and the workpiece and
• (2) the time during which each detector element that has the workpiece in its field of view is exposed to radiation orginating from each of said radiation sources and reflected from the workpiece,
• that each such detector element is, during a brief time interval, exposed to radiation which is reflected to it from substantially one and the same small surface area on the workpiece but which originates first from one and then from the other of said two radiation sources.

Apparatus for obtaining information about surface configuration of a workpiece, said apparatus being of the type comprising a photoresponsive detector element which has an optical axis and which produces an output having a magnitude dependent upon the intensity of radiation that it detects within a response field limited to small angles of divergence from said optical axis, means for causing said detector element to scan at an ascertainable velocity in a direction substantially normal to its optical axis across a workpiece that extends across its response field, and a pair of radiation sources that are spaced to opposite sides of said optical axis and each of which emits radiation in a direction away from said detector element and obliquely across said axis for reflection from a workpiece to said element, said apparatus being characterized by:

• A. means for defining a succession of measurement cycle time intervals that are of a uniform and substantially short duration which is so related to the velocity of scan that there is a substantial overlap between the respective local areas of a workpiece surface which are within said response field at the beginning and at the end of each measurement cycle time interval;
• and
• B. means for restricting exposure of said detector element to radiation which, during every radiation cycle, originates alternately from each of said radiation sources substantially to the exclusion of radiation originating from the other and which is reflected from a workpiece.