Patent ID: 8564851

Claim:
A scanning system having dual mounting heads that define a measurement gap, which has a web entry end and a web exit end that is downstream from the web entry end, and which is configured to accommodate a continuous web that has a first side and a second side and that travels in a downstream direction, which comprises: (a) a first elongated member that extends along a first direction wherein the first elongated member supports a first mobile mounting head that is disposed adjacent to the first side of the web, the first mobile mounting head including a first operative surface facing the first side of the web; (b) means for driving the first mobile mounting head; (c) a second elongated member that extends along a second direction that is parallel to the first direction wherein the second elongated member supports a second mobile mounting head that is disposed adjacent to the second side of the web, the second mobile mounting head including a second operative surface facing the second side of the web, wherein the first operative surface and the second operative surface define the measurement gap through which the continuous web travels; (d) means for driving the second mobile mounting head such that movement of the first mobile mounting head is synchronized with movement of the second mobile mounting head; (e) an alignment error generating means for generating error signals representing a difference in alignment between the first and second mobile mounting heads as the first and second mobile mounting heads scan back and forth along a translation axis; and (f) actuator means for regulating relative positions of the first mobile mounting head and/or the second mobile mounting head, wherein the actuator means is controlled by the error signals.