Abstract:
A low current switch has a flexible movable contact that can be deflected by an actuator. In some implementations the switch may permit a low current switch to be manufactured using elements of a high current switch without requiring large amounts of precious metal. The flexible movable contact may be arranged as one or more cantilevers that are deflected using a rocking actuator. The actuator interacts with the movable contact in such a way as to provide tactile feedback to an operator comparable to a high current switch having a rigid movable contact. Also described are a set of low and high current switches, components of a low current switch, and a method of manufacturing a low current switch.

Description:
FIELD OF THE INVENTION 
     The invention relates to the design of electrical switches, and more specifically to a low-current switch design. 
     BACKGROUND OF THE INVENTION 
     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. 
     SUMMARY OF THE INVENTION 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a switch according to aspects of the invention. 
         FIG. 2  is another cross-sectional view of the switch shown in  FIG. 1 , illustrating a second position of the switch. 
         FIG. 3  is a three-dimensional view of components of the switch shown in  FIG. 1 . 
         FIG. 4  is another cross-sectional view of the switch shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a cross-sectional view of an example switch  100  which illustrates aspects of the invention. 
     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  FIG. 1 , may increase the durability of flexible element  150 , and may resist the effect of material fatigue tending decrease the contact gap over the life of the switch. However, in some implementations return-assist  155  and projection  135  may be omitted without departing from some aspects of the invention. In some implementations, projection  135  may be formed in one piece with, or be anchored or attached to terminal  130 . In some implementations, projection  135  may be formed in one piece with, or be anchored or attached to housing  110 . 
       FIG. 2  is another cross-sectional view of switch  100 , illustrating a second position of switch  100 . 
     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  FIG. 1 ) to the second position, bearing surface  165  no longer biases flexible element  150  (or the bias is reduced). The spring action of flexible element  150  biases both flexible element  150  and contact  180  away from contact  170  such that terminal  130  and terminal  120  are no longer in electrical communication. Return-assist  155  also interacts with projection  135  to bias flexible element  150  and contact  180  away from contact  170 . 
     In  FIG. 1 , actuator  160  includes a rocking surface  161  seated on a pivot surface  131  of housing  110 . Rocking surface  161  may be rounded or pointed as desired, in order to configure switch  100  as a two-position switch.  FIG. 2  shows rocking surface  261 , which is configured as a flat surface having two corners. The configuration of rocking surface  261  may be used to configure switch  100  as a three-position center-off switch, alone or in combination with detent  999 . However, other pivot structures may be used. 
     As illustrated in  FIGS. 1 and 2 , switch  100  also includes a terminal  140  having a contact  270 , a contact  280 , bearing surface  265 , stopping surface  267 , return-assist  255 , and projection  235 . Each of these components operate and interact with one another in the same manner as terminal  120 , contact  170 , contact  180 , bearing surface  165 , stopping surface  167 , return-assist  155 , and projection  135  respectively, such that movement from the second position to a third position of the switch (not shown) will cause bearing surface  265  to bias flexible element  150  and contact  280  toward contact  270  such that terminal  140  and terminal  130  are in electrical communication. The third position (not shown) is functionally symmetrical with the first position shown in  FIG. 1 . In this configuration, terminal  130  is a common terminal of switch  100 . 
     The second position shown in  FIG. 2  represents a center-off position of the SPDT arrangement of switch  100 ; however, those having skill in the art will appreciate that the components can be configured to eliminate the stable center-off position. 
     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). 
       FIG. 3  is a three-dimensional view illustrating some of the components of switch  100 . 
     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 . 
       FIG. 4  is another cross-sectional view of the switch  100  shown in  FIG. 1 , further illustrating the geometry of 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.