Patent Application
20070295114
The present disclosure generally relates to improvements to an accelerated weathering device, and more particularly, to an indoor accelerated weathering device equipped with an optical slip ring disposed between a light collection device and a sensor.
Accelerated weathering devices are used to simulate adverse weather conditions, such as rain, wind, and sunlight, on specimens in order to anticipate the conduct of certain materials over extended periods of time. For example, designers of a new paint formulation, who cannot wait years for test results, may wish to know if their product can withstand severe weather conditions over a period of years without adverse change in appearance or performance. Accelerated weathering devices may be programmed to simulate the desired condition over shorter periods of time. Some models of indoor accelerated weathering devices use a rotating rack to mount test specimens and submit samples to an artificial environment to simulate accelerated weathering condition such as humidity, temperature, wind, atmospheric pressure, and light exposure. Such models are described in U.S. Pat. Nos. 5,503,032 and 5,646,358 and are hereby fully incorporated herein by reference.
Among the environmental parameters to be varied to recreate desired changing weather conditions is exposure to light. Light often simulates the irradiating energy from the sun in an accelerated daily cycles. A light source can also constitute a secondary heat source in the test area. If an intense light is placed at the center of a generally spherical test volume, all test samples located on the test plane created by the surface of a sphere at a fixed distance from the light will be subject to similar levels of photonic activity. The intensity of the light source must be closely monitored in order to regulate the intensity of the activity on the test plane, control the accelerated weathering conditions, and obtain meaningful test results.
Regulation and monitoring of the light source within the test chamber as disclosed in the prior art and U.S. Pat. Nos. 5,503,032 and 5,646,358, hereby fully incorporated herein by reference, are conducted in either of two unsatisfactory ways. In the first, a battery-powered wireless radiometer detector equipped with a light sensor is mounted on the rotating specimen rack alongside the test specimens. In the second, a front-end optical input sensor is mounted on a fixed axis at some fixed point off the specimen plane. Both configurations present significant disadvantages that eventually translate either into the introduction of complex mathematical correction factors within the results of the tests or rapid degradation of the detection material.
In the first conventional configuration, the wireless radiometer detector is located on the test plane of the test samples but is subject to such other environmental factors as heat, humidity, pressures, and gravitational forces associated with a revolving test specimen plane. The wireless radiometer detector must relay the signals to a fixed radiometer and the entire radiometer. A fragile electro-optic sensor placed in the hostile environment of the weathering device test chamber is submitted to the accelerated weathering conditions of the device. The effective time the detector can continuously measure is limited by the data storage capacity of the device and/or the battery life. The light detected must also be transformed by the detector into an electronic signal using the limited processing capacity of the small device, which then transports the data from the rotating specimen plane to the control mechanism via an electrical slip ring.
The second conventional configuration consists of using a light sensor, possibly attached to a light guide at a fixed point in the chamber outside of the moving specimen plane. In current weathering instruments, the front-end optics consist of a quartz rod that guides the light from the lamp out of the exposure chamber to a photodiode. The photodiode converts the light to an electrical signal that is then sent to the control system electronics. As a result of the measurement being conducted at a different location, the measured intensity of the light will be different than the light received at the specimen plane, so correction factors must be introduced within the results in order to compensate for this variation. These correction factors, based on extrapolation, introduce error factors that are detrimental to the ultimate determination of the sample reaction under fixed accelerated weathering conditions. The sensor, if placed between the samples and the light source, also introduces shading to part of the specimen plane. If the sensor is placed in the back of the sample plane, it is partly shaded by the specimens.
Other test chamber parameters, such as temperature, are relayed from the rotating rack to the fixed measurement chamber through an electrical slip ring. An electrical slip ring is a device equipped with ball bearings, a rotor, and a stator able to transfer electrical signals from a rotating body to a stationary body. In an electrical slip ring, the signals are passed from a rotating conductor to a stationary conductor via conducting brushes. Since an electrical slip ring only relays electrical signals, the light signal from a light sensor must first to be converted into an electrical signal for the information to be relayed to the electronic monitoring and control system.
In the field of accelerated weathering devices, complex mathematical extrapolation formulas are already needed to correlate forced, short-term cycling conditions with actual, long-term weathering conditions. The disadvantage of placing front-end optics of the light monitoring system in any location other than adjacent a sample creates the need for a compensating factor to be added to the model. The application of a compensating factor is also discouraged.
Therefore, a need exists in the art for a weathering system configuration that facilitates irradiance measurement on the rotating sample plane while maintaining sensitive electro-optical components outside the accelerated weathering environment.
This disclosure describes an indoor accelerated weathering device having a rotatable rack in a test chamber used for mounting specimens in an exposure plane. The rack is equipped on the sample plane with a light collection device that is operatively couple with a fixed light collection device by a light wave guide functionally connected to an optical rotary joint. In one embodiment an optical slip ring is used as an optical rotary joint.
Certain embodiments are shown in the drawings. However, it is understood that the present disclosure is not limited to the arrangements and instrumentality shown in the attached drawings, wherein:
For the purpose of promoting and understanding the principles disclosed herein, reference is made to the preferred embodiments illustrated in the drawings, and specific language is used to describe the same. It is nevertheless understood that no limitation of the scope is thereby intended. Such alterations and further modifications in the illustrated device and such further applications are the principles disclosed as illustrated therein as being contemplated as would normally occur to one skilled in the art to which this disclosure relates.
In one embodiment, the rack 1 is supported by a top support member or shaft 6 that extends through a top wall of the test chamber 2 of the device.
It is also be understood by one of ordinary skill in the art that while the rack 1 as shown on
It is understood by one of ordinary skill in the art that, while test specimens 3 are shown as rectangular plates on
The light collection device 7 connected to the rack 1 in the exposure plane 4 may be comprised of input optics comprising a cosine-type receptor 13 and a light diffuser 14. It is understood by one of ordinary skill in the art that the cosine-type receptor 13 relates to a specifically designed type of diffuser receptor, generally of white molded plastic, designed to correct the reading of the light diffuser based on the cosine law. The cosine law refers to the relationship between the irradiance on a surface and the incident angle. The light intensity falls off in proportion to the cosine of the reflected angle since the effective surface area is reduced as the angle increases. The cosine-type receptor 13 and the light diffuser 14 allow for the automatic correction of the intensity of the light received on the test specimen 3 if the test specimen 3 is located on the rack 1 where the reflected angle of incidence may differ. While one specific type of input optics 7 is disclosed as the preferred embodiment, it is understood by one of skill in the art that any other similar type and technology of detector can be used.
In the preferred embodiments shown in
A light wave guide 9 is shown to operatively couple the light collection device 7 to an optical rotary joint 8.
In one preferred embodiment, the optical rotary joint is a fiber optic rotary joint (FORJ). While the use of electrical slip rings to trasfer data from a rotating rack 1 to a nonrotating electronic monitoring and control system 23 is disclosed in the prior art, the use of an optical slip ring to transfer light from a rotating rack 1 in the field of accelerated weathering devices is new. A FORJ is a device that allows the transmission of power, electrical signals, and light signals from rotating structure to a stationary structure. The light transfer capacity of the FORJ is fully described in U.S. Pat. No. 4,492,427. All other power and control signals pass through standard copper slip rings also included in the FORJ and allow for the transfer of other information and instrumentation from the rack 1 to the stationary device.
It is understood by one of ordinary skill in the art that, while one possible configuration of optical rotary joint 8 is shown in
In one preferred embodiment, the sensor is equipped at a minimum with a controller 17 used to regulate and control the intensity of the light source 5 within the test chamber 2. The microprocessor 18 is used to process and analyze the data from the photosensitive element 19. The information from the sensor may be sent to the electronic monitoring and control system 23 to be recorded for further reference within the test result.
In another possible embodiment, the optical rotary joint 8 may also include a sensor for transferring the optical light from the light wave guide 9 into electronic data to be processed directly by the electronic monitoring and control system 23.
Furthermore, while particular preferred embodiments have been shown and described, it is obvious to those skilled in the art that changes and modifications may be made without departing from the spirit and teaching of the disclosure. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as limitation. The actual scope of the disclosure is intended to be defined in the following claims when viewed in their proper perspective based on the related art.
