Optical Projector: Working Principle and Overview
Introduction to Optical Projectors
An optical projector, also known as a digital projector, is a precision measuring instrument that combines optical, mechanical, and electronic measurement technologies. It is widely used in industries requiring high-precision two-dimensional measurements, such as mold making, tooling, spring and screw manufacturing, gear and cam production, thread analysis, clockmaking, automatic lathe processing, and aerospace. Optical projectors play a critical role in manufacturing, quality control inspections, and academic research.
Working Principle of an Optical Projector
The optical projector operates by creating an enlarged real image of a workpiece on a projection screen. In the setup shown in Figure 1, under reflected illumination, the objective lens (U) projects an enlarged, reversed image (Y2) onto the frosted surface of the projection screen (M) through mirrors (G1 and G2). This results in an image that appears as the inverse of the workpiece.
When the objective lens and reflector system are adjusted to an upright image configuration, Y2 displays as an erect image, mirroring the workpiece’s orientation directly. The workpiece’s enlarged image is displayed on the screen, and its contour is measured with a digital measuring system, which includes an electronic ruler and either a DC-3000 or QC200 data processor. A rotation angle digital display system on the projection screen also enables measurement of the workpiece’s contour angle.
The system’s illumination sources, including reflectors (F1 and F2) and lighting sources (S1 and S2), provide transmission and reflection lighting, adjustable according to the workpiece’s properties. A half-mirror (B) is used exclusively for reflected illumination.
Overall Structure of the Optical Projector
The optical projector mainly comprises three components: the projection box, the main shell, and the worktable.
- Projection Box: Contains the imaging system, including the objective lens, mirrors (G1 and G2), the projection screen, and the DC-3000 data processor. The projection screen rotation mechanism has an angle sensor for precise angle measurement.
- Main Shell: Houses the lighting, electrical control systems, and a cooling fan. It also provides structural support for the projection box and worktable.
- Worktable: Allows movement along the X-axis (longitudinal), Y-axis (lateral) for coordinate measurements, and Z-axis (vertical) for focusing. The X and Y axes include grating scales with a resolution of 0.001mm.
A more detailed view of each component’s structure is shown in Figure 1.
Imaging Types in Optical Projectors
Optical projectors can display two types of images: positive (upright) and negative (reversed) images.
Measurement Functions of the Optical Projector
Optical projectors offer a variety of measurement functions, including:
- Multi-point acquisition for determining straight lines and circles
- Preset functions for different geometric elements
- Combination measurements for each geometric element
- Coordinate rotation and translation
- Adjustable Z-axis as a sensor length value or code
- User self-programming capability
- Polar and rectangular coordinate conversions
- Grating ruler linear and segment linearity correction functions
- RS232 input functionality
- Print page input functionality
- Power failure memory function
- Storage and retrieval of geometric elements