Imaging and inspection apparatus and method

Object detection apparatus comprising:

• source means producing an output beam of radiation having non-uniform distribution of intensity thereacross;
• means supporting the object for relative movement along an axis substantially orthogonal to the path of the beam for interrupting the beam initially at the periphery thereof;
• detector means disposed to detect the relative intensities of the interrupted beam in at least four individual sectors which are oriented in orthogonal quadrants about a central sector for producing outputs representative of the intensity of the interrupted beam at each such sector thereof;
• circuit means connected to receive the outputs for additively combining the outputs of the four sectors and for subtracting therefrom the output of the central sector to provide a composite output that attains substantially zero value as an indication of the position of the object within the beam along the axis of movement.

The method of detecting the edge of an object interposed in a beam of light having a non-uniform distribution of power density across the beam, the method comprising the steps of:

• orienting the object for relative movement along an axis substantially orthogonal to the path of the beam for interrupting the beam initially at the periphery thereof;
• detecting the relative intensities of the interrupted beam in a central sector and in a peripheral sector oriented about said central sector for producing outputs of said sectors representative of the interrupted beam;
• and
• sensing the difference of said outputs to provide a composite output that indicates the position of the object within the beam along the axis of movement in response to the composite output attaining substantially zero value.

Object detection apparatus comprising:

• source means producing an output beam of radiation having non-uniform distribution of density thereacross;
• means supporting the object for relative movement along an axis substantially orthogonal to the path of the beam for interrupting the beam initially at the periphery thereof;
• detector means disposed to detect the relative intensities of the interrupted beam in a central sector and in a peripheral sector oriented about said central sector for producing outputs representative of the intensity of the interrupted beam at each such sector thereof;
• circuit means connected to receive the outputs for producing an output indicative of the difference of the outputs of said sectors to provide an indication of the position of the object within the beam along the axis of movement.