Method for actuating an electromechanical switching element

Abstract

The invention relates to a method for actuating an electromechanical switching element at least comprising: a plurality of contacts; a coil having an iron core; and an armature, wherein, in the event that a predefined condition is fulfilled, the switching element is repeatedly pulsed on and off during the switch-off process or pulsed off and on during the switch-on process at a predefined point in time within an overtravel range in such a way that the coil current flowing into the coil oscillates between a predefined maximum value and a minimum value so that the armature moves within the overtravel range, thereby causing the contacts to rub against one another without becoming detached from one another, the minimum value being defined as the current value at the point in time at which the armature begins to detach from the iron core.

Description

[0001] Method for controlling an electromechanical switching element

[0002] The invention relates to a method for controlling an electromechanical switching element, as well as a universal component.

[0003] Two types of errors can occur when switching electromechanical switching elements such as relays. In one case, a relay may not make contact when switched on, while in another case the current flow through the contacts may not be interrupted when switched off. There are many reasons for these errors, including mechanical jamming, oxide layers, and welding of the contacts. However, the majority of the reasons are reversible. This means that if the contacts have become mechanically jammed once, they can still be released and the relay can continue to be used for many thousands of switching cycles. This makes it possible to correct a faulty switching state of a relay by actuating it again.

[0004] In DE102014211400A1, for example, the contactor is opened and closed at least once if the contacts of the contactor come into contact with a contact resistance that is not below a defined value.

[0005] In EP3185269B1, the operating current is superimposed on an electrical waveform. This method is only applicable for a turn-off process.

[0006] Measures such as repeating the switching process and applying vibration to the contacts are known. The measurement technology required to detect contact states is also known, for example, from DE 102018114425 A1 or WO 202194418 A1.

[0007] However, the known methods still need to be improved to prevent or delay failures of switching elements.

[0008] Therefore, it is an object of this invention to provide a method for controlling an electromechanical switching element by which sticky contact elements can be avoided or released again. This object is achieved according to the invention by the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims.

[0009] A method is proposed for controlling an electromechanical switching element, at least having a plurality of contacts, a coil with an iron core and an armature, wherein, if a predetermined condition is met, the switching element is pulsed on and off during the switching-off process or pulsed on and off during the switching-on process at a predetermined time within an overtravel range several times in such a way that the coil current flowing into the coil oscillates between a predetermined maximum value and a minimum value, so that the armature moves within the overtravel range and as a result the contacts rub against one another without separating from one another, wherein the minimum value is defined as the current value at the time at which the armature begins to separate from the iron core.

[0010] In a further embodiment, it is provided that the predetermined condition is a detected fault condition in which the contacts do not contact when switched on or do not release when switched off, or wherein the predetermined condition is a detection of a deterioration in the contact quality of the contacts.

[0011] In a further embodiment, it is provided that the duty cycle or the off-time is selected until the coil current has reached the value it had at a predetermined time after switching off or switching on.

[0012] In a further embodiment, it is provided that for each electromechanical switching element, the overtravel range is continuously determined during use, and in the event that this changes during the service life, the predetermined time for pulsing in or out is adjusted within the overtravel range.

[0013] In a further embodiment, continuous monitoring is provided to determine whether the specified condition is met. In a further embodiment, a universal component is provided, comprising an electromechanical switching element having a plurality of contacts and an armature, wherein the armature is configured to move the contacts such that they touch or separate from one another, and an integrated measuring system for determining at least one overtravel range during operation of the electromechanical switching element, and a microcontroller in signal communication with the electromechanical switching element, in which the method is implemented as a software program.

[0014] In a further embodiment, the universal component is designed as a relay socket.

[0015] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which illustrate details of the invention, and from the claims. The individual features can be implemented individually or in combination in a variant of the invention.

[0016] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. They show:

[0017] Figures 1-3 show views of an electromechanical switching element in different switching states according to the prior art.

[0018] Figure 4 shows a diagram with a normal shutdown process and rubbing of the contacts according to an embodiment of the present invention.

[0019] In the following descriptions of the figures, the same elements or functions are provided with the same reference symbols.

[0020] The proposed method is used in products with electromechanical switching elements 10 that have a plurality of contacts 7a, 7b, 7c and an armature 5. In particular, electromechanical switching elements 10 of the proposed invention are installed in universal components such as universal sockets, which are used, for example, in industrial automation (DC industrial networks) or in charging stations for electric vehicles, etc. The electromechanical switching elements 10 used here cannot generally be configured directly after production or based on one or more reference components, since depending on the application scenario, i.e. type of switching element, control voltage, installation position, installation location, etc., different influences act, which can lead to changed properties of the switching properties of the switching element.

[0021] Therefore, according to the invention, an electromechanical switching element 10 is controlled directly at the installation site to reduce errors. This means that the control process is carried out within the universal component. This requires both measurement technology and a microcontroller, which are installed in the universal component. The universal component can be designed as a relay socket.

[0022] In the following, reference is made only to a relay 10 as the electromechanical switching element 10. However, the method can also be used for other electromechanical switching elements, e.g., contactors. In addition to the embodiment shown here, in which a changeover contact is a component of an electromechanical switching element 10, the changeover contact of this type can also be integrated into other devices, such as a changeover switch.

[0023] Figure 1 shows a schematic representation of a three-pole changeover contact according to a general embodiment. In this case, the changeover contact is merely an example of a part of an electromechanical switching element 10 or changeover relay. The electromechanical switching element 10 comprises three terminals assigned to the changeover contact, which are referred to below in accordance with the usual convention as the COM terminal ("common") 2a, the NC terminal 2b (normally closed), and the NO terminal 2c (normally open). Furthermore, the electromechanical switching element 10 comprises two relay coil terminals 3a and 3b, via which a relay coil 3, also referred to as coil 3 for short, of the electromechanical switching element 10 can be energized with a coil current I3.Via the current flow, the relay coil 3 builds up a magnetic field which is guided in a magnetic core 4 and exerts a force on a movable relay armature 5, also referred to as armature 5 for short, which in turn causes a movement of one or more contacts 7a, 7b, 7c (also referred to as contact elements or contact pills) assigned to the respective terminals 2a, 2b, 2c via a slider 6.

[0024] Figure 1 shows a state in which relay 10 is open, i.e. contacts 7a and 7b are in contact with one another. Figure 2 shows a state in which the relay is closed, i.e. contacts 7a and 7c are in contact with one another. Figure 3 shows a so-called overtravel. Here, contact 7a is in contact with contact 7c (relay 10 is closed) and is pressed against contact 7c by slide 6 actuated by armature 5, which is represented by the bending of the upper end of contact 7a. When relay 10 is switched on and off, there is a region in which contacts 7a and 7c are in contact, but armature 5 does not touch coil 3 (more precisely, iron core 8). This means that the connection between contacts 7a and 7c is already conductive, but the bending of the contact elements is still changing; this region is referred to below as the overtravel region.

[0025] Figure 4 shows the temporal progression of a switching-off process for an electromechanical switching element 10, e.g., formed as a relay, according to the prior art. A normalized measured variable x / X_max is indicated on the ordinate. Here, the region B0 denotes the state in which the relay 10 is closed, i.e. the armature 5 is attracted to the coil 3; more precisely, the armature does not touch the coil 3, but rather the yoke or iron core 8 and detaches from it in regions B1 and B2, and the contacts 7a and 7c abut one another (as in Fig. 2), so that conductivity exists (denoted by the short dashed line L1). The region B1 denotes the state of the overtravel (as in Fig. 3), at which the armature 5 is detachable from the coil 3, but the contacts 7a, 7c are not yet detachable from one another.Area B2 shows the state in which the relay 10 is open, i.e. the contacts 7a, 7c are separated from each other, so that there is no longer any conductivity between the contacts 7a, 7c (as in Fig. 1 ). The solid line represents the coil current I3. It can be seen that during the switch-off process the coil current I3 decreases until it reaches a current minimum (minimum current) at time t_01. This current minimum is defined by the release of the armature 5 from the iron core 8 of the coil 3 (and can be detected shortly after the release). At time t_01, at which the armature 5 begins to release, the coil current I3 increases again, which can be determined mathematically, for example, via the derivative (change from negative to positive). At this time t_01, area B0 changes into area B1 (overtravel). At the time t_12, when the contacts 7a, 7c open, the overtravel area B1 is left (area B2, in which the contacts 7a, 7c are open).The period d_02 refers to the time period between t_01 and t_12, in which the armature 5 is detached from the iron core 8 of the coil 3, but the contacts 7a, 7c are still in contact with each other.

[0026] The aim of the invention is to detect a faulty switching state that prevents contacts 7a / 7b or 7a / 7c from separating from one another, or in which contacts 7a / 7b or 7a / 7c touch but do not conduct, and to automatically correct this faulty switching state. This is achieved by re-energizing armature 5 within the overtravel range B1, causing contacts 7a, 7c to move and rub against one another, as described below. In particular, the opening process, i.e., contacts 7a, 7c, is considered. However, the proposed method can also be applied during opening. Depending on the installation, there are two switch-off errors in the changeover contact (NO 2c-COM 2a; COM 2a-NC 2b), but also switch-on errors for these contact pairs, so that a total of four errors are corrected in the changeover relay: contacts NO 2c-COM 2a do not release, NO 2c-COM 2a do not conduct, COM 2a-NC 2b do not release, COM 2a-NC 2b do not conduct.

[0027] Since the focus below is on the switch-off process, the method is described only with reference to contacts 7a and 7c. The corresponding parameters, e.g., I1, t_on, d_on, L2, are also shown in Figure 4 to clarify the operation of the method.

[0028] The excitation, in this embodiment a renewed switching on or pulsing (since no complete switching on process is carried out), takes place at a time t_on within the overtravel range B1 , i.e. within the time period d_02. Advantageously, the time t_on is chosen so that it is at a (temporal) distance from t_01 and t_12. The choice of the time t_on can be made arbitrarily by the microcontroller. From this time t_on, the coil current, referred to below as I1, increases again (shown in Figure 4 as a dashed line starting at t_on), preventing the contacts 7a, 7c from releasing. However, they are still excited within the overtravel range and are moved from one another by the spring force on different trajectories, so that the contacts rub against one another or forces are exerted on a connection between the contacts.As the coil current 11 rises again, the contacts 7a, 7c are pressed together again. When the coil current 11 reaches a predetermined current value, which was selected during the turn-off process at a time t_off, the device is turned off again, causing the contacts 7a, 7c to be excited again and moved from one another by the spring force along different trajectories, so that the contacts rub against one another, or forces are exerted on a connection between the contacts. This can be repeated several times. This creates friction between the contacts 7a, 7c without them separating from one another, i.e., without a complete switching cycle being completed. The switching element 10 is therefore fully conductive even while the contacts are rubbing.The coil current I3 (11) thus oscillates between a (predetermined, freely selected) maximum current and a (defined by the release of the armature 5) minimum current, which always causes a movement of the armature 5 in the overtravel range B1.

[0029] The turn-off time t_off is selected somewhere between the maximum current (maximum coil current I3) indicated by "1" on the ordinate in Figure 4 and the minimum current (present at time t_01). In this embodiment, the turn-off time t_off is selected at approximately 2 / 3 of the full coil current I3. However, a different turn-off time t_off, and thus a different turn-off coil current I3, can also be selected for each control. For example, excitation can occur in a range from 90% to 40% of the coil current I3.

[0030] The off-duty d_off results from the selected time t_off and the switch-on time t_on. The switch-on duration d_on results from the period between the switch-on time t_on and the time t_off2 at which the coil current I1 reaches the same level as the switch-off coil current I3 at the time t_off. The sum of d_off and d_on results in the frequency of the (pulse width) signal for control, and the ratio of d_off and d_on results in the duty cycle of the signal. A high frequency of 50 Hz or more is preferably achieved, in this embodiment 200 Hz. The method is advantageously terminated at the earliest when successful contacting of the contacts 7a, 7b (when switching on) or release of the contacts 7a, 7c (when switching off) is detected. Monitoring is advantageously carried out continuously or at predetermined times.If no corresponding detection is possible after a specified period of time, relay 10 is switched off and an error signal is output.

[0031] The result of the proposed renewed excitation is that the contacts 7a, 7c rub against each other several times, but are not opened (separated from each other), so that the conductive connection between them remains, as indicated by the dotted line L2 in Figure 4. The term "multiple" means that the pulsing and depulsing (in the switching-off process) or the pulsing and depulsing (in the switching-on process) is repeated several times, preferably until the fault condition is no longer detected, whereby a limitation to a duration or frequency of the rubbing can be provided.

[0032] Furthermore, during excitation, a complete switching cycle is not completed. Rather, a new excitation occurs within the overtravel range B1, i.e., within the period d_02 between the release of armature 5 and the release of contacts 7a, 7c at a time t_on, i.e., before contacts 7a, 7c separate from each other.

[0033] The process is event-based and is advantageously executed when a fault condition has been detected, i.e., when contacts 7a, 7c do not release or when a conductive connection can no longer be established due to deposits. The friction resulting from the multiple pulsing (during the switch-off process) or the pulsing (during the switch-on process) loosens contaminants between the contacts or rubs off applied material.

[0034] However, the method can also be executed under conditions other than a currently detected fault condition, e.g., preventively. It can be executed based on the detection of an impending fault condition, i.e., preventively. If, for example, oscillation in the coil current I3 is detected at the end of a switching operation, it can be concluded that the switching element 10 is in a state of degradation (deterioration in the contact quality of the contacts 7a, 7b, 7c). Although no fault condition has yet been detected in which the contacts 7a, 7c no longer separate from one another (when the relay 10 is switched off) or do not establish a conductive connection (when the relay 10 is switched on), the fault condition is already becoming apparent and is therefore expected. The method can then be executed preventively.

[0035] In a less preferred embodiment, the method can also be carried out preventively after a fixed number of switching operations of the relay 10.

[0036] As already mentioned, the procedure can be carried out both in the switch-on process and in the switch-off process, since in both processes the error condition can occur that the contacts 7a / 7c, 7a / 7b do not separate from each other or do not conduct.

[0037] In order for the method to be carried out, at the beginning of the use of the electromechanical switching element 10, i.e. after installation in the application, data (coil current I3, times t) are collected during each switching operation in order to be able to determine the overtravel range B1. As already described above, this can be determined from the time difference between the first change in sign of the time derivative of the coil current and the first change in the conductivity of the contacts 7a / 7c, 7a / 7b. By collecting the data during as every switching operation as possible, the overtravel range B1 can be adjusted, which can shift over its service life, for example, due to the aging of the relay 10. The method is therefore adaptive.

[0038] In order to record the data and carry out the adjustment, a universal component is provided which has both the required measuring technology, e.g. for measuring current, and a microcontroller which can perform the corresponding calculations and controls the relay 10. The method is implemented as a software program in the microcontroller. It also serves to control the relay 10, e.g. using a PWM signal. One advantage of the method is that many system failures caused by faulty relays 10 can be prevented. In addition, the system has a short response time, which means that the operation of the system can continue uninterrupted. A further advantage of the method is that the friction can be stopped immediately if the device is not switched on again, since there is no oscillation behavior. In addition, the technical implementation as a self-contained universal switching component ensures minimal application effort for the user.

[0039] List of reference symbols

[0040] COM port

[0041] 2b NC connection

[0042] 2c NO connection

[0043] 3 Relay coil

[0044] 3a, 3b relay coil connections

[0045] 4 magnetic core

[0046] 5 relay armatures

[0047] 6 sliders

[0048] 7a-7c Contact elements

[0049] 8 iron core

[0050] 10 electromechanical switching element, e.g. relay

[0051] BO anchor position contacts closed

[0052] B1 Anchor position overstroke (overstroke range)

[0053] B2 anchor position contacts open

[0054] I3 coil current

[0055] 11 Coil current during rubbing

[0056] I3_max, I1_max Maximum coil current

[0057] I3_min Minimum value of coil current L1, L2 Conductivity t Time t_off Switch-off time t_off2 Switch-off time friction t_on Switch-on time t_12 Time at which contacts open t_01 Time at which armature releases d_02 Period / duration overtravel d_off Switch-off duration d_on Switch-on duration

Claims

Patent claims 1 . Method for controlling an electromechanical switching element (10), comprising at least several contacts (7a, 7b, 7c), a coil (3) with an iron core (8) and an armature (5), wherein - in case a given condition is met, - in the switching-off process, pulsing and unpulsing of the switching element (10) is carried out several times at a predetermined time (t_on) within an overtravel range (B1) in such a way that the coil current (I3, I1) flowing into the coil (3) oscillates between a predetermined maximum value (I3_max; I1_max) and a minimum value (I3_min), so that the armature (5) moves within the overtravel range (B1) and as a result the contacts (7a, 7b, 7c) rub against one another without separating from one another, the minimum value (I3_min) being defined as the current value at the time (t_01) at which the armature (5) begins to separate from the iron core (8).

2. Method according to claim 1, wherein the predetermined condition is a detected fault condition in which the contacts do not contact when switched on or do not release when switched off, or wherein the predetermined condition is a detection of a deterioration in the contact quality of the contacts (7a, 7b, 7c).

3. Method according to claim 1 or 2, wherein the switch-on period (d_on) or the switch-off period is selected until the coil current (11) has reached the value which it had at a predetermined time (t_off) after switching off or switching on.

4. Method according to one of the preceding claims, wherein for each electromechanical switching element (10) the overtravel range (B1) is determined continuously during use, and in the event that this changes during the service life, the predetermined time (t_ein) for pulsing in or out is adapted within the overtravel range (B1).

5. Method according to one of the preceding claims, wherein continuous monitoring is carried out to determine whether the predetermined condition is met.

6. Universal component (100), comprising: - an electromechanical switching element (10) having a plurality of contacts (7a, 7b, 7c) and an armature (5), wherein the armature is arranged to move the contacts (7a, 7b, 7c) such that they touch or separate from each other, and - an integrated measuring technology for determining at least one overtravel range (B1) during operation of the electromechanical switching element (10), and - a microcontroller in signal communication with the electromechanical switching element (10), in which the method according to one of the preceding claims is implemented as a software program.

7. Universal component (100) according to claim 6, which is designed as a relay socket.

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