Patent Application
20210108970
Many smoke detectors work by allowing air, including smoke and other particulates, from the surrounding environment into a chamber. The chamber has a light source and a light sensor. Depending on the type of smoke detector, smoke within the chamber may be detected by the scattering of light from the light source by particulates within the chamber, or by obfuscation of light from the light source.
Many heat detectors use a device, typically a thermistor, whose characteristics change with temperature.
Combination detectors combine various sensors into a single detector. In such detectors, the current amount of smoke, the rate of change of smoke, the temperature and the rate of change in temperature may all or in part be used to determine the presence of a fire.
In the assembly of smoke sensor/detector, a thermistor is typically fed manually through the chamber base and hand-soldered to a printed circuit board (PCB). Although inefficient, this is possible because the current thermistor is robust and has sufficient mass to be manipulated during assembly.
The thermistor 156 is a critical component, but the current hand-assembly process needed to install it is highly inefficient. As
Due to a change in regulatory requirements, new sensors and detectors must use an even more sensitive thermistor, such as an NTC 226K thermistor, to meet the new standard. The new thermistor component may be much smaller and delicate, and more difficult to work with in high-volume production than the currently used thermistor. Without the new housing described herein, the bottleneck in the production/assembly process would be expected to become even more severe than it already is. The annual demand for sensors and detectors using this new thermistor may be in the millions, leading to millions of minutes of production inefficiency annually.
Since the new thermistor component is much smaller and more delicate, the current assembly process is neither efficient, viable, nor repeatable, especially in high-volume production. The novel thermistor housing described herein effectively addresses these problems. The thermistor housing makes the thermistor itself more robust without diminishing performance, reduces assembly cycle times, is self-retaining in the chamber base for soldering, and creates a more repeatable and accurate assembly process. It also improves the process flow and cycle time of a high-volume product. Without the thermistor housing described herein, there is a large risk of high levels of defects caused during the assembly process, creating a bottleneck that could affect the ability to meet demand. The thermistor housing makes the assembly process scalable to the level needed to meet demand, and could even make assembly with the older, larger thermistor more efficient.
The thermistor housing has a number of critical features, described in more detail herein. The design incorporates features that protect the thermistor without reducing functionality, and that improve the ease of assembly into mating components. The housing has been designed to consistently prepare thermistors for assembly by controlling the height of the thermistor and the separation distance of the leads. This is a critical achievement because the manual labor needed to prepare the thermistor by hand would create a significant bottleneck in the assembly process. The thermistor housing reduces assembly cycle time, creates a repeatable assembly process, and makes the thermistor itself more robust.
In testing, prototypes of the thermistor housing reduced assembly cycle times, the number of defects during assembly, and the scrap rate during assembly. Furthermore, a consistent and repeatable assembly process has been achieved.
Accordingly, an embodiment of a housing assembly for holding a component may have two parts wherein a first part has a crimp clearance region into which a deformable section on the second part may be displaced to secure the component leads such that the component is fixed in the housing. The housing assembly may be configured to be mounted onto a base.
The housing assembly may further include a crush rib configured to retain the component to the base.
Either part of the housing assembly may include component lead channels/grooves, wherein the other part of the housing assembly has matching component lead ribs that mate with the lead channels when the first and second parts are assembled together. Both housing assembly parts may include partial lead guides such that when the housing parts are assembled together, the partial lead guides of one part mate with the partial lead guides of the other part to form fully formed lead guides for guiding the component leads into the component lead channels. The component lead channels may be configured to direct leads of the component to a printed circuit board.
Furthermore, in an embodiment, the housing assembly may be keyed so that it can only be installed onto a chamber base in specific orientations. For example, the housing assembly may have at least one flat side and one rounded side.
In a further embodiment, the housing assembly may further include at least one guide peg configured to be inserted into corresponding holes in a printed circuit board (PCB). The pegs may extend beyond the component leads to protect the component leads from being damaged and help to align the component leads with corresponding thru-holes on the PCB. Additionally, the housing assembly may have a predetermined length to hold the component at a predetermined distance from the base.
In an embodiment, the component may be a thermistor.
An embodiment of a thermistor sub-assembly may include a housing assembly comprising a first housing part and a second housing part, as well as a thermistor secured in place in the housing assembly.
A hazard detector, according to an embodiment of the present invention, may include a housing assembly having first and second parts. One of the parts may comprise a deformable section, while the other part includes a crimp clearance region into which the deformable section may be displaced to secure component leads such that the component, for example a thermistor, is fixed in the housing to form a component housing assembly. The component housing assembly may be configured to be mounted onto a base, wherein at least one of the housing parts has a crush rib configured to hold the component housing assembly in place on the base. A printed circuit board (PCB) may be located behind and proximate to the base, wherein the component housing assembly and the base direct component leads through the base to predetermined thru-holes in the PCB. The housing assembly may have a predetermined length wherein when it is mounted onto the base, the component is a predetermined distance from the base, such that the component protrudes through a hole in a detector cover. The hazard detector may be, for example, a combination smoke and heat detector.
According to an embodiment, a method for assembling a thermistor sub-assembly may include attaching a first housing part to a second housing part to form a thermistor housing, at least one of the first and second parts comprising at least one plastic plug, and the other of the first and second parts comprising a corresponding hole for each plastic plug, each plug extending through its corresponding hole. The thermistor's leads may then be inserted into the thermistor housing. The plastic plugs may then be cold-staked to secure the two housing parts to each other. The thermistor leads may be secured to the thermistor housing by deforming at least one deformable section of one part into a crimp clearance section of the other part.
Alternatively, a method for assembling a hazard detector having a detector sensor and a base may include assembling a component sub-assembly having a crush rib on the sub-assembly's outer surface. The component sub-assembly may then be inserted into the base, wherein the crush rib secures the component sub-assembly the base.
Manually placing an electrical component such as a thermistor is not a very efficient process and is prone to mistakes. For smaller and more delicate thermistors, the current assembly process is even less efficient, less viable, and less repeatable, especially in high-volume production. The thermistor housing described herein addresses this problem with many novel features.
The thermistor housing makes the thermistor itself more robust without diminishing performance, reduces assembly cycle times, is self-retaining in the chamber base for soldering, and creates a more repeatable and accurate assembly process.
The thermistor housing improves the manufacturing process flow and cycle time of a high volume product. Without the thermistor housing, there is a large risk of high numbers of defects caused during the assembly process, creating a bottleneck that could affect the ability to meet demand. The thermistor housing makes the assembly process scalable to the level needed to meet demand.
The housing 200 is formed by assembling two mating parts: a first housing part 201 and a second housing part 221. When assembled together, these two housing parts 201, 221 combine to form two wedge-shaped funnels 205 at one end of the housing that receive the thermistor leads 253 and serve to separate the leads to the proper spacing for PCB assembly. The leads are conducted through the housing 200 and the ends of the leads (only one lead end shown at 254) protrude out the other end of the housing 200. Protective guide pegs 255 protect the thermistor lead ends 254 and guide the housing through the chamber base (
Plastic bosses 209 may be cold-staked, locking the two halves of the housing together. Once the thermistor 251 is inserted into the housing 200, wire crimping features (one for each lead) 222 on the second housing part 221 are distorted into matching crimping spaces 211 on the first housing part 201, securing the thermistor leads 253 and the thermistor 251 to the housing 200 and setting the proper height of the thermistor. Conversely, the thermistor may be inserted into the housing 200 and the cold-staking and crimping may be performed simultaneously.
A crush rib 223 allows the thermistor housing to be self-retaining in the chamber base.
As can be seen in
When the thermistor housing assembly is placed into the mounting hole (see
Similar to
There are various methods of assembly that can utilize the thermistor housing.
For example, the two parts 201 and 221 may first be assembled together to form the housing assembly. The thermistor 251 may then be inserted and secured in the housing as described above, and the completed thermistor subassembly 200 may then be plugged into the chamber base mounting hole 707.
Alternatively, the plastic housing may be assembled together, and then the housing alone may be plugged into the chamber base. The thermistor may then be fed into the housing which guides the leads through the PCB holes. In this case, of course, the cold staking and crimping would not be done simultaneously.
In yet another alternative, a single-piece housing may be molded around the leads of the thermistor. The over-molded assembly may then be plugged into the chamber base which guides the leads of the thermistor through the PCB holes.
It would be understood by one skilled in the art that while many of the features described herein are described as being on the first part 201 or the second part 221 of the housing, many of these features could be on the other part than that described. For instance, the crush rib 223 may be located on the first part 201 or the second part 221. For that matter, each part 201, 221 may have a crush rib. Further, it does not matter which part comprises a groove as long as the other part comprises a matching rib.
For clarification of claim terms, a “housing assembly” is an assembly of two or more parts that, when assembled together, are configured to hold an electrical component, such as (but limited to) a thermistor, LED, photosensor in place a predetermined distance away from a printed circuit board or base, such as a smoke chamber base. A “component housing assembly” is a housing assembly plus an electrical component installed therein. A “thermistor housing assembly” is a component housing assembly wherein the electrical component is a thermistor.
While the invention is illustrated in the drawings and described herein, this disclosure is to be considered as illustrative and not restrictive in character. The present disclosure is exemplary in nature and all changes, equivalents, and modifications that come within the spirit of the invention are included. The detailed description is included herein to discuss aspects of the examples illustrated in the drawings for the purpose of promoting an understanding of the principles of the invention. No limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described examples, and any further applications of the principles described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. Some examples are disclosed in detail, however some features that may not be relevant may have been left out for the sake of clarity.
Singular forms “a”, “an”, “the”, and the like include plural referents unless expressly discussed otherwise. As an illustration, references to “a device” or “the device” include one or more of such devices and equivalents thereof.
Directional terms, such as “up”, “down”, “top” “bottom”, “fore”, “aft”, “lateral”, “longitudinal”, “radial”, “circumferential”, “behind”, etc., are used herein solely for the convenience of the reader in order to aid in the reader's understanding of the illustrated examples. The use of these directional terms does not in any manner limit the described, illustrated, and/or claimed features to a specific direction and/or orientation.
