US 6954271 B2
A spectrometer for measuring the intensity of light, comprises a grating having a major axis, a first entrance aperture aligned with the grating major axis and configured to direct light energy onto the grating, wherein the grating is adapted to produce a focused light beam, a first exit aperture aligned with the grating major axis and configured to accept the focused light beam, a second entrance aperture configured to direct the light energy onto the grating, wherein the second entrance aperture is offset from the grating major axis, and a second exit aperture configured to accept the focused light beam.
1. A multiple input spectrometer, comprising:
a grating having a surface and a major axis perpendicular to the surface; and
a light plate, the light plate comprising a plurality of entrance slits, wherein at least one of the plurality of entrance slits is offset from the grating major axis, wherein the light plate further comprises a plurality of exit slits, wherein at least one of the plurality of exit slits is offset from the grating major axis.
2. The spectrometer of
means for directing a light source at the light plate; and
means for simultaneously obtaining a spectra measurement through each of the plurality of exit slits.
The present invention pertains to spectrometer analysis and more particularly to the simultaneous measurement of several spectral properties using a single spectrometer.
Optical spectrometers allow the study of a large variety of samples over a wide range of wavelengths. Materials can be studied in the solid, liquid, or gas phase either in a pure form or in mixtures. Various designs allow the study of spectra as a function of temperature, pressure, and external magnetic fields.
Grating spectrometers, in particular, make use of the diffraction of light from a regularly spaced ruled surface. They disperse the light by a combination of diffraction and interference rather than the refractive index variation with wavelength. The normal operation of a grating is the same as with a prism. The grating is rotated, and wavelength after wavelength passes a field stop and is detected by a sensor. In general, a grating spectrometer operates by focusing the light through an optical system to the field stop. In a classical spectrometer the field stop is a slit. This light is then collimated and passes through a transmission grating or passed to a reflective grating. The dispersed light is then either focused onto a spectral array or through an exit slit to a detector where it can be analyzed. While plane gratings require separate collimating optics, concave gratings combine the function of the grating and collimating optics into a single optical component.
Near-Infrared (NIR) spectroscopy is one of the most rapidly growing methodologies in pharmaceutical analysis. In particular, NIR is being increasingly used as an inspection method during the packaging process of pharmaceuticals, often augmenting or replacing previously used vision inspection systems. For example, an NIR inspection system can be used to inspect a blister packaging for, among other things, proper filling, physical aberrations, chemical composition, moisture content, and proper package arrangement.
The use of vision systems as an inspection mechanism is becoming less and less sufficient as the need for more in depth inspection procedures, and near 100% inspection processes, are desired and in many cases required. Of particular note is that vision systems are not capable of performing any sort of chemical analysis of the product being packaged, relying only on a comparison of a visual snapshot of the package to a reference image. A typical vision packaging inspection system “looks” at each individual package to see whether it has the correct number of doses in the pack, i.e. the system looks for missing or overfilled tablet wells. In some cases, physical discrepancies such as cracks or gouges on a tablet, will also cause a rejection of the package. The limitations of these types of vision systems become apparent when they are compared with the capabilities of a spectrometer adapted to function in a pharmaceutical packaging and inspection facility.
In high speed, large-volume processing, automated spectrometer-based monitoring systems have become indispensable in examining product flow in order to detect irregularities. Since these systems are meant in large part to replace vision systems, accuracy is a critical factor.
Known spectrometer designs typically incorporate a single entrance slit (field stop) and a single exit slit. The single exit slit typically corresponds to a single detector or other sensor and the measurement system requires a separate spectrometer (including entrance slit, exit slit, and grating) for each required simultaneous spectrum measurement. When multiple simultaneous spectrum measurements are desired, the cost and complexity of a spectrometer system capable of performing such analysis increases dramatically, particularly because of the need for multiple gratings. What is needed is a device and method that provides for multiple and simultaneous spectrum measurements while only requiring a single spectrometer.
In one aspect, a spectrometer having a reflective grating and the grating having a major axis, a light plate, comprises a plurality of entrance apertures, wherein at least one of the entrance apertures is offset from the grating major axis.
In another aspect, a spectrometer for measuring the intensity of light, comprises a grating having a major axis, a first entrance aperture aligned with the grating major axis and configured to direct light energy onto the grating, wherein the grating is adapted to produce a focused light beam, a first exit aperture aligned with the grating major axis and configured to accept the focused light beam, a second entrance aperture configured to direct the light energy onto the grating, wherein the second entrance aperture is offset from the grating major axis, and a second exit aperture configured to accept the focused light beam.
As will become apparent to those skilled in the art, numerous other embodiments and aspects will become evident hereinafter from the following descriptions and claims.
The drawings illustrate both the design and utility of the preferred embodiments of the present invention, wherein:
Positioned on the conveyer 110 is a pharmaceutical packaging unit 132 such as a blister pack, tablet well, ampul, or vial. As the packaging unit 132 passes the spectrometer head 105, it has already been filled with a product, such as a tablet or capsule 130, and is ready for inspection. The filling step typically occurs at a prior point in the manufacturing process. Typically, the packaging unit 132, filled with the tablets 130, are aligned in one or more rows 135 a, 135 b, and 135 c. As positioned on the conveyer 110, each of the rows 135 a, 135 b, and 135 c correspond to one of the sensors 115 a, 115 b, and 115 c. The spectrometer head 105 is aligned so that each of the sensors 115 a, 115 b, and 115 c are positioned substantially over a corresponding row 135 a, 135 b, or 135 c. As the conveyer 110 moves each packaging unit 132 past the spectrometer head 105, a corresponding packaging unit 132 passes under one of the sensors 115 a, 115 b, and 115 c. Readings taken by the sensors are fed to the spectrometer head 105 where information about the individual tablets 130 in the packaging unit 132 is analyzed. Defective or otherwise unacceptable packages/tablets are rejected at a subsequent stage in the manufacturing and packaging process. A computer 140 is linked to the spectrometer head 105 and is adapted to analyze the data gathered by the inspection system 100. Statistical information or other analytical data can be gathered by the computer 140 and sent to an operator for viewing or stored for later review and analysis.
In known systems, inspection systems are adapted so that each sensor is linked to a separate spectrometer and is therefore capable of only a single spectrum measurement at any given time, i.e. only one tablet can be inspected at a time by each sensor. A sensor must therefore take a separate reading for each tablet (or other product) contained within each packaging unit.
A white light source 205 illuminates the tablet 130 passing on the conveyer 110 and generates reflected light energy 207. The reflected light energy 207 is collected by the sensor 115 a and is passed into the spectrometer 200 as incoming light energy 210. In some applications, and as shown in
It is generally understood that spectrometer designs incorporate a single entrance slit aligned with the major axis of the grating. This arrangement is referred to herein as an on-axis alignment and an on-axis entrance slit. Off-axis entrance slits, i.e. entrance slits that are not aligned with the major axis of the grating but are rather offset from the major axis, are known to result in the introduction of aberrations into the spectrum being measured. This degradation in performance is generally not acceptable for analytical measurements that require high precision and accuracy.
For those applications, however, where precision and accuracy of the raw spectrographic measurement is not a critical factor, the allowable tolerances of the spectral measurement allows for a certain amount of aberrations in the measured spectrum. For example, when accepting or rejecting a group of tablets based on the similarity of that group's spectrum as compared with the spectrum of known good tablets, such aberrations do not affect the performance of the system or the resulting measurements. Since this type of comparison is relative rather than absolute, the aberrations that perturb the spectrum do not influence the comparison as long as the perturbations are static. Known approaches to tablet inspection require that all spectra are measured with spectrometers having equivalent characteristics and therefore will not tolerate the introduction of these types of aberrations.
After the sampled light energy passes through each of the entrance slits 320 a, 320 b, and 320 c, it is directed as light rays 325 a, 325 b, and 325 c onto the grating 330. The orientation and construction of the grating 330 determines which wavelength of the light is reflected and focused as light rays 345 a, 345 b, and 345 c. The grating 330 as shown in
Also positioned within the spectrometer 300 are a series of detectors 360 a, 360 b, and 360 c. Each of the detectors 360 a, 360 b, and 360 c is positioned adjacent an exit light plate (350 a, 350 b, and 350 c respectively). Each of the exit light plates 350 a, 350 b, and 350 c includes an exit slit 355 a, 355 b, and 355 c. The reflected light rays 345 a, 345 b, and 345 c are directed at each of the exit slits 355 a, 355 b, and 355 c respectively. Detectors 360 a, 360 b, and 360 c are positioned behind each of the exit slits. The detectors function to analyze the light energy that is passed through each of the respective exit slits 355 a, 355 b, and 355 c. Alternately, each of the detector and exit slit pairs may be replaced with a detector array so that various wavelengths may be measured simultaneously without the need to rotate the grating.
The three entrance slit/exit slit/detector arrangement of the multiplexed spectrometer 300 can be utilized to analyze three different light energy samples simultaneously (by having three separate inputs to the entrance light plates/entrance slits). Increased throughput in an inspection systems utilizing such an arrangement is thereby realized because three tablets can be inspected simultaneously by a single spectrometer. Since the location of the off-axis entrance slits 320 a and 320 c are static, so are the aberrations that are reflected in the spectrum results from the corresponding samples. Since the aberrations are static, the relative spectrum measurements are not influenced and the comparison is not affected.
Although the present invention is particularly suited for use in connection with pharmaceutical capsules and tablets, it is to be clearly understood that the principals of this invention as well as the invention itself are applicable to and may be employed in connection with countless different types and kinds of solid discrete particular objects, including solid or multi-colored objects, liquids, powders, and various other substances.
Although the present invention has been described and illustrated in the above description and drawings, it is understood that this description is by example only and that numerous changes and modifications can be made by those skilled in the art without departing from the true spirit and scope of the invention. The invention, therefore, is not to be restricted, except by the following claims and their equivalents.