Patent Application
20140251777
The invention relates to the design of electrical switches, and more specifically to a low-current switch design.
In many electrical systems it is common to locate a low current switch next to a high current switch on a panel. This makes sense, for example, if a particular subsystem uses a high current switch as a power control, and a low current switch as a signaling control.
Typically, it is also desirable for such switches to have the same functional “feel” so as to maintain a common tactile response for the operator. This is especially the case where the switches have a similar or matching exterior design. If these switches “feel different” during switching, the operator may mistakenly believe that one of the switches is beginning to fail, or may think that the overall fit and finish of the system is poor.
Under these aesthetic constraints, it is tempting to simply use a duplicate high current switch for a low current application, on the assumption that it will be able to handle the lower current just as well. However, the design requirements for low current switches are considerably different than for high current switches. For this reason, it is often impossible or impractical to substitute switches in this way. The challenge then is to devise an economical way to create a low current switch that has a “feel” that matches a corresponding high current switch to an acceptable degree.
In order to approach this problem, it is important to consider the design requirements of each of these types of switches. Some of the major design differences between low and high current switches relate to the effects of corrosion and switch bounce.
Low current switches are more susceptible to corrosion of contacting surfaces than switches used in high current applications, and must be designed to more aggressively minimize corrosion. Low current switches are also frequently used in applications that are sensitive to noisy signal transitions, and are best designed to minimize this effect, which is usually not an issue in high current applications. These differing requirements have an effect on the structure, “feel,” and manufacturing cost of the switch.
Using typical materials, corrosion can build up on the contacting surfaces over time, particularly in wet or corrosive environments. This corrosion forms an insulating barrier that increases resistance and interferes with the electrical contact.
High current switches can tolerate a certain degree of tarnish or corrosion on contacting surfaces because the high current is sufficient to “punch through” the corrosion. For a given switch design, the minimum current required to break through the expected corrosion resistance is commonly known as the “wetting current”.
Wetting current is the lowest current that an electronic circuit can operate under. Below the wetting current, current will not flow at all. However in low current applications, the current is usually below the wetting current for a typical high current switch. This means that the current in the system may be insufficient to “punch through” the corrosion that forms on the contacting surfaces, eventually causing the switch to fail.
In order to address this issue for low current applications, the contact points and certain types of conducting joints (such as pivot or bearing surfaces) within the switch must be made from or coated with a minimally corroding substance in order to prevent the gradual buildup of tarnish or other corrosion.
Gold plating is a standard choice for providing a highly conductive and non-corroding surface. However gold is very expensive, with costs increasing dramatically in recent years.
Because it is so expensive, the gold plating used in switches is often extremely thin in order to reduce costs. If the coating is made too thin, however, this can negatively impact reliability by making the switch overly susceptible to wear-through and eventual corrosion.
This means that adapting a typical pivoting high-current contact switch for use in low current applications by simply adding gold plating can represent a significant increase in materials cost, and may not be sufficient to produce a low current switch having a sufficiently long life.
Because of these issues, a low current switch based on a high current design may need to be structurally redesigned to minimize the amount of gold that is required. However, these modifications have the potential to change the feel of the switch.
Low current applications are also often susceptible to switch contact bounce. This is particularly true in digital circuits where an unambiguous transition between signaling levels can be important for proper operation.
Switch bounce occurs when the contacts of the switch open and close. As the contacts come together, the mass, inertia, and surface characteristics of the contact cause the contacts to “bounce” or rapidly open and close several times before coming to rest in the closed position. A similar effect can occur as the contacts separate and before they come to rest in the open position.
Because high current circuits are usually not especially sensitive to noisy switching signals, such switches are frequently designed to handle the desired current load without regard to bounce. Thus, the structures of a high current switch may produce signals that are too noisy for some low-current digital signaling applications.
In order to use such a switch for low current applications, the circuit being switched may need to be “debounced” using additional components in order to create a reliable signal. However debouncing circuitry requires additional cost to manufacture. In some high speed digital applications a delay is introduced to adequately debounce a switch designed for high current use.
Because of these issues, a low current switch based on a high current design may need to be structurally redesigned to minimize switch bounce. But as with a redesign to reduce corrosion with a minimum of gold plating, these modifications have the potential to alter the feel of the switch.
It is therefore desired to provide a low current switch that addresses these deficiencies.
Objects of the invention are achieved by providing a switch which includes a flexible element fixedly attached within a housing, which extends from a fixedly attached portion to an unattached end and is in electrical communication with a first terminal; a contact in electrical communication with a second terminal; an actuator which is configured to move between a first position and a second position and to bias the flexible element such that the unattached end flexes toward the contact when the actuator is moved from the second position to the first position; a switch handle having a handle bearing surface in contact with the actuator and configured to move the actuator between the second position and the first position; and, a return assist attached to the flexible element and configured to bias the unattached end away from the contact. The flexible element may include a flat spring.
In some implementations, the return assist includes a tongue attached at the unattached end of the flexible element and extending toward the fixedly attached portion. The switch may include a projection disposed to contact the return assist, and the projection may be configured to bias the flexible element away from the contact.
In some implementations, when the actuator is in the first position, the flexible element is in electrical communication with the contact. The actuator may include a stopping surface configured to prevent the actuator from travelling from the second position past the first position.
In some implementations, the handle bearing surface comprises a roller. In some implementations, the handle bearing surface is configured to slide against the actuator. In some implementations, the switch handle comprises a spring piston, and the spring piston may bias the handle bearing surface against the actuator. In some implementations, the flexible element is fixed by staking, and optionally, may be staked to the first terminal.
Other objects of the invention are achieved by providing a switch that includes a flexible element rigidly attached within a housing, which extends from a rigidly attached portion to an unattached end and is in electrical communication with a first terminal; a contact in electrical communication with a second terminal; an actuator which is configured to move between a first position and a second position and to bias the flexible element such that the unattached end flexes toward the contact when the actuator is moved from the second position to the first position; a switch handle having a handle bearing surface in contact with the actuator and configured to move the actuator between the second position and the first position; and, a return assist attached to the flexible element and configured to bias the unattached end away from the contact.
Further objects of the invention are achieved by providing a switch that includes a flexible element non-pivotally attached with respect to a housing, which extends from a non-pivotally attached portion to an unattached end and is in electrical communication with a first terminal; a contact in electrical communication with a second terminal; an actuator which is configured to move between a first position and a second position and to bias the flexible element such that the unattached end flexes toward the contact when the actuator is moved from the second position to the first position; a switch handle having a handle bearing surface in contact with the actuator and configured to move the actuator between the second position and the first position; and, a return assist attached to the flexible element and configured to bias the unattached end away from the contact.
Still other objects of the invention are achieved by providing a switch that includes a flexible element disposed within a housing, which is in electrical communication with a first terminal; a contact in electrical communication with a second terminal; an actuator which is configured to move between a first position and a second position and to bias the flexible element toward the contact when the actuator is moved from the second position to the first position; a switch handle having a handle bearing surface in contact with the actuator and configured to move the actuator between the second position and the first position; and, a return assist attached to the flexible element and configured to bias the unattached end away from the contact; where the switch actuator includes a first bearing surface about which the actuator is configured to pivot between the first position and the second position, a second bearing surface configured to apply pressure to the flexible element, and a third bearing surface configured to interact with the switch handle.
In some implementations, the actuator includes a fourth bearing surface configured to interact with a stop such that the actuator is prevented from pivoting beyond the first position from the second position.
In accordance with another aspect of the present invention, a method of manufacturing a switch includes providing a flexible element fixedly attached within a housing, which extends from a fixedly attached portion to an unattached end and is in electrical communication with a first terminal; providing a contact in electrical communication with a second terminal; providing an actuator which is configured to move between a first position and a second position and to bias the flexible element such that the unattached end flexes toward the contact when the actuator is moved from the second position to the first position; providing a switch handle having a handle bearing surface in contact with the actuator and configured to move the actuator between the second position and the first position; and, providing a return assist attached to the flexible element and configured to bias the unattached end away from the contact.
Further objects of the invention and its particular features and advantages will become more apparent from consideration of the following drawings and accompanying detailed description.
Switch 100 is a single-pole double-throw (“SPDT”) switch having a housing 110, first, second, and third terminals 120, 130, 140, and a flexible element 150 attached to terminal 130. Switch 100 may be adapted for use as a low-current switch, for example, in applications rated for 28 mA 12V or 14 mA 24V, or less.
In example switch 100, flexible element 150 is a flat spring which is made from of a suitable material that is electrically conductive. For example, flexible element 150 may be comprised of spring copper or another suitable metal, or may be comprised of a metalized plastic having the desired resiliency, flexibility, spring, and conductive properties.
Actuator 160 is disposed within housing 110 and is shown in a first position, where it biases flexible element 150 and contact 180 toward contact 170 such that terminal 130 and terminal 120 are in electrical communication. In some implementations, Contacts 170 and 180 may include a “contact tape.” In some implementations, contacts 170 and 180 may each include an elongated angled structure, and be configured such that the elongated angled structures are disposed substantially at right angles to one another, and such that they contact at a crossing point. This can have the advantages of reducing switch bounce and increasing the life of the contacts. The use of an angled structure in this way can also have the advantage of helping to break through any oxide that may have formed on the contact tape due to the increased pressure focused on a small contact point. Further, the use of an angled structure may also have the advantage of reducing the chances of interference due to particulate matter settling on the contacts, due to their small contacting surface area. Contact 180 may be omitted in some configurations.
Switch handle 190 interacts with actuator 160 in order to move it between the first position shown and other positions. Switch handle 190 is shown featuring a spring-piston arrangement incorporating a roller 195 for engagement with a surface 197 of actuator 160.
Actuator 160 has a bearing surface 165 which presses on flexible element 150 when actuator 160 is in the first position shown, in order to bias flexible element 150 toward contact 170.
In some implementations, the use of a bearing surface to bias a flexible element in this way can have the advantage of reducing the amount of bounce exhibited at the contacts 170, 180 by absorbing impact energy from the mechanism.
Actuator 160 also has a stopping surface 167 which prevents actuator 160 from travelling past the first position in one direction. This can have the advantage of preventing excess strain on flexible element 150, although stopping surface 167 may be omitted without departing from some aspects of the invention.
Flexible element 150 is shown with a return-assist 155 that interacts with projection 135 to further bias flexible element 150 away from contact 170. This can have the advantage of improving the break-contact performance of flexible element 150 when actuator 160 is moved out of the first position shown in
In the second position shown, switch handle 190 and actuator 160 are shown in a neutral second position. A detent 999 is provided in actuator 160 which engages with roller 195 to assist in providing a stable “center-off” position. However, those having skill in the art will appreciate that detent 999 may be omitted, such as when configuring switch 100 to operate without a stable center-off position. After the actuator 160 moves from the first position (shown in
In
As illustrated in
The second position shown in
Further, those having skill in the art will appreciate that switch 100 can be reconfigured as a single-pole-single-throw (“SPST”) switch (not shown) by omitting the structures associated with the third position (not shown).
Bearing surface 165 is shown biasing flexible element 150 and contact 180 toward contact 170 in the direction of arrow 300 as a force is applied to the actuator 160 by switch handle 190. At the same time, both return-assist 155 and other portions of flexible element 150 resist the applied force. In some implementations, bearing surface 165 contacts flexible element 150 at a compliant location. This can have the advantage of reducing contact bounce. Bearing surface 165 may also comprise multiple bearing surfaces each biasing flexible element 150.
Flexible element 150 is shown anchored by connection 350 to a portion of terminal 130. Connection 350 may be formed by staking flexible element 150 to terminal 130, although other types of connections are possible, such as ultrasonic bonding, spot-welding, or soldering, for example. Because a staked connection may be considered to be a high-pressure metal-to-metal joint, the joint does not require gold plating for low-current applications.
The electrically contacting portions of switch 100, i.e. contacts 170, 180, 270, and 280 may be plated, clad, or otherwise covered with gold or another minimally corroding material. Because only these surfaces of switch 100 require protection from contact oxidation in low current applications, switch 100 may have the advantage of reducing the cost of producing the switch by decreasing the amount of precious metal required.
In example switch 100, flexible element 150 can be described as forming a pair of cantilever springs; one extending toward terminal 120, and the other extending toward terminal 140, each from a fixed end formed by connection 350. It will be evident to those having skill in the art that switch 100 could be reconfigured as a single-throw switch by eliminating one of the cantilevers and its associated components and geometry within the switch.
Return-assist 155 can be described as another cantilever having a fixed end formed from a free end of the flexible element 150, and having a free end extending toward the connection 350. The free end and sides of return-assist 155 are separated from other portions of flexible element 150 by a gap, cut, and/or slit through flexible element 150, and return-assist 155 may be machined, stamped, etched, or otherwise formed from or with flexible element 150. In alternate configurations, a return-assist may be fabricated from a separate piece (not shown) and attached to flexible element 150.
Although the invention has been described with reference to a particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements or features, and indeed many modifications and variations will be ascertainable to those of skill in the art.
| Number | Date | Country | |
|---|---|---|---|
| 61774286 | Mar 2013 | US |
