Variable focal length lens system with optical power monitoring

An optical power monitoring configuration for use in a variable focal length (VFL) lens system,

• the VFL lens system comprising:
• a VFL lens;
• a VFL lens controller that controls the VFL lens to periodically modulate the optical power of the VFL lens over a range of optical powers at an operating frequency;
• an objective lens that inputs workpiece light arising from a workpiece surface during a workpiece imaging mode and transmits the workpiece light along an imaging optical path that passes through the VFL lens;
• and
• a camera that receives the workpiece light transmitted by the VFL lens along the imaging optical path during the workpiece imaging mode and provides a corresponding workpiece image exposure;
• and
• the optical power monitoring configuration comprising:
• a monitoring beam generator comprising a light source and a beam pattern element that is configured to input light from the light source and output a monitored beam pattern, wherein:
• the optical power monitoring configuration is configured to transmit the monitored beam pattern along at least a portion of the imaging optical path to travel through the VFL lens to the camera during an optical power monitoring mode such that the camera provides at least a first monitoring image exposure including the monitored beam pattern during at least a first phase timing of the periodic modulation of the VFL lens during the optical power monitoring mode, and a dimension of the monitored beam pattern in the first monitoring image exposure is related to an optical power of the VFL lens during the first phase timing.

A computer implemented method for operating a variable focal length (VFL) lens system, the VFL lens system comprising a VFL lens, a VFL lens controller, an objective lens and a camera, the computer implemented method comprising:

• under control of one or more computing systems configured with executable instructions,
• controlling the VFL lens to periodically modulate an optical power of the VFL lens over a range of optical powers at an operating frequency;
• initiating a workpiece imaging mode, the workpiece imaging mode including utilizing workpiece imaging light settings and operating the camera to receive workpiece light transmitted by the VFL lens along an imaging optical path to provide at least one corresponding workpiece image exposure, wherein the imaging optical path includes the objective lens which is configured to input workpiece light arising from a workpiece surface and to transmit the workpiece light along the imaging optical path that passes through the VFL lens;
• determining that an optical power monitoring mode is to be initiated;
• initiating the optical power monitoring mode, the optical power monitoring mode including utilizing monitoring light settings and operating the camera to receive a monitored beam pattern and to provide a plurality of monitoring image exposures including the monitored beam pattern, wherein an optical power monitoring configuration comprises a monitoring beam generator comprising a monitoring light source utilized for the monitoring light settings and a beam pattern element that inputs light from the monitoring light source and outputs the monitored beam pattern, and the optical power monitoring configuration is configured to transmit the monitored beam pattern along at least a portion of the imaging optical path to travel through the VFL lens to the camera during the optical power monitoring mode, and each of the monitoring image exposures corresponds to a respective phase timing of the periodic modulation of the VFL lens, and at least one dimension of the monitored beam pattern in each respective monitoring image exposure is related to an optical power of the VFL lens during the respective phase timing;
• measuring the at least one dimension of the monitored beam pattern in each of the monitoring image exposures;
• determining that at least one adjustment to the operation of the VFL lens will be made based at least in part on the measured at least one dimension of the monitored beam pattern in each of the monitoring image exposures;
• and
• performing the at least one adjustment to the operation of the VFL lens.