Some calibration providers will place a linear scale on a machine, take some measurements, give you a report and call it a day. A proper calibration is much more involved, especially if the machine has additional sensors such as touchprobe or laser. Below is an overview of a few of the critical mechanical alignments we perform on every service visit and the different calibrations necessary for accurate measurements.
Parfocalization adjusts the optics so the part image stays in focus through the full zoom range, from high to low magnification.
Rotational alignment ensures the camera axis is parallel to the stage axis. This mechanical alignment is critical to measurement accuracy because if the camera is rotated, the measured position of features will change from one side of the camera to the other.
Coaxial alignment aligns the video camera to the centerline axis of the zoom lens. If the coaxial alignment is incorrect, measured features will appear to move when zooming in and out. This would result in positional errors in features if measured at different zooms. The camera is mechanically aligned to the zoom lens, afterward a zoom calibration is done to remove any small remaining errors.
The AccuCentric LED retical assembly is used to recalibrate the optical system whenever you change the zoom position (magnification). The retical must be aligned to the camera for the system to work properly. Over time, the retical alignment can drift, causing errors when zooming, especially at high magnification.
Optics Calibration ensures that an edge can be measured accurately anywhere within the field of view. During the Optics Calibration, the system:
- Calibrates the field of view so an edge can be accurately located anywhere within the field of view.
- Calibrates the zoom lens through its entire zoom range from high to low magnification.
The Optics Calibration should be performed at every calibration visit, whether mechanical adjustments were performed or not.
Each additional add-on lens requires a separate Optics Calibration.
This calibration minimizes the effect of astigmatism errors in the zoom lens assembly. If these errors are not corrected, Z values returned from an autofocus may vary depending on the type and orientation of the part being measured. This calibration is performed at the highest magnification, where the Z measurement accuracy is the highest.
Each additional add-on lens requires a separate Autofocus Calibration
Non-Linear XY Stage Calibration
Stage calibration ensures maximum stage travel accuracy over the entire XY measuring area. The measurement software measures a chrome-on-glass artifact with a pattern of crosses, creates and applies a pattern correction to compensate for normal wear over time. The correction factors vary depending on the location of the stage.
Z Axis Calibration
The Z axis is calibrated using a certified step gage with known distances between each step and the level base. The step gage is superior to gage blocks because it can be leveled to the machine axes. It provides a means of calibrating and verifying the measurement accuracy of the Z axis using optical focus, touchprobe or laser.
If the machine is equipped with a TTL or DRS laser, it is important that it's adjusted and calibrated to the optical sensor. With the DRS, the laser is attached to the side of the optical assembly. The exact offset distance is measured and the optics and laser are calibrated to each other. For the TTL laser, which is coincident to the optics, the sensor is mechanically aligned to the optics and the laser range is calibrated.