Patent Application
20210138812
Equipment and machinery is often capable of injuring a user when it is operated unsafely. For example, a printing system may can cause injury if it is operated with a cover or a door open, e.g., a cover or a door located in a compartment such as a compartment within a carriage. Therefore, the open cover or door can be considered as an unsafe condition. Safety interlock mechanisms are designed to prevent equipment and machinery from operating when an unsafe condition exists.
Examples will now be described, by way of non-limiting examples, with reference to the accompanying drawings, in which:
Safety interlock mechanisms are mechanisms that comprise a set of switches mechanically coupled to and/or actuated by a part of a system such as, e.g., a door and electrically coupled to a relay and/or a load. The main purpose of the safety interlock mechanism is to prevent a load from being powered if a safety condition is not fulfilled, e.g., if a door is open.
Safety interlock mechanisms are relevant mechanisms within any device that may potentially cause risk on a user. Interlock mechanisms are of such an importance that several jurisdictions recommend specific certifications to be able to sell products including them.
It is useful for safety interlock mechanisms to comply with several certifications to prevent their malfunction and, furthermore, it is a further feature for interlock mechanisms comprising a plurality of switches to be able to determine the status of each of the switches as to have the ability to warn the user exactly which switch of the set of switches presents the unsafe situation.
In the foregoing, reference is made to the accompanying drawings. The examples in the description and drawings should be considered illustrative and are not to be considered as limiting to the specific example or element described. Multiple examples may be derived from the following description and/or drawings through modification, combination or variation of certain elements. Although certain features are shown and described in conjunction they may be applied separately, also if not specifically claimed. Furthermore, it may be understood that examples or elements that are not literally described may be derived from the description and drawings by a person of ordinary skill in the art.
The switches 50, 51, 52 are coupled to an actuator 20, 21, 22 for example, mechanically coupled. In the example of
Further, the interlock mechanism is connected, on one side to a source Vin and, on the other side to a relay 41 which upon receiving a voltage from the source Vin energizes a circuit 42.
Since the interlock mechanism 1 comprises a set of serially connected switches, it suffices that one of the switches 50, 51, 52 does not have the contact towards the relay 41 in a conductive state to de-energize the relay and, as a consequence, disable the circuit 42. It is useful to de-energize a relay if an unsafe condition occurs and, further, it is also useful to know specifically where the unsafe condition occurred, i.e., which switch is not in conductive state.
Therefore, the interlock mechanism 1 comprises a detection circuit 3 associated to at least one of the switches 50, 51, 52 and connected to its second contact, e.g., the normally closed contact. The detection circuit 3 according to an example is a detection circuit that is isolated from the relay 41 as to prevent that a malfunction of the detection circuit erroneously activates it. In
The detection circuit 3 is, in an example, an active circuit, i.e., a circuit comprising an energy source. In a further example, the detection circuit is a circuit able to inject a current through the switches 50, 51, 52 while the switches are conductive in the contact that is connected to the detection circuit 3, i.e., the second contact. In such an example, the circuit may comprise a set of auxiliary resistors 500, 501, 502 on the intermediate nodes 53, 54 to close the detection circuit when the second contact is active.
If there is an unsafe condition, the first actuator 20 acts on the first switch 50 and closes the detection circuit 3. Then, if VM is a voltage higher than Vi, (for example 110% Vi or 110% higher than the maximum voltage calculated for the corresponding intermediate node) a current flow occurs from the detector source 31 through the measurement resistor 32, the second contact of the switch 50, and the auxiliary resistor 500. In this case, a voltage drop occurs on the measurement resistor 32 which is indicative that an unsafe condition may be occurring on the compartment associated to the first actuator 20.
In this case, a voltage measurement circuit connected to the measurement resistor 32 may be used to establish that the first switch 50 is detecting an unsafe condition. This same working principle can be extended to the second actuator 21 and the third 22.
A relevant feature of having an active detection circuit 3 is that, even if the adjacent serially connected switches are open, the circuit is able to inject a current to the intermediate node 53, 54, while it is isolated from the relay 41 and, in consequence, allows for a safe measurement.
The detection circuit 3 of
In the foregoing, to explain the working principle of the detection circuit, reference will be made to the second switch 51, however, a similar functioning applies to other switches within the interlocking mechanism 1.
On the first condition, if the second actuator 21 is on an active position the switch is on a position wherein the first contact is in conductive state. In this case, the drain resistor 37 does not close a circuit so there is no voltage drop on the emitter -base of the transistor 34, therefore, the transistor is on an off state and there is also no current trough the collector-drain arrangement of the transistor. Therefore, a detector 33 connected to the drain will detect a zero.
On the second condition, if the second actuator 21 is on passive state, the switch moves to a position wherein the second contact is in conductive state. In this case, the drain resistor 37 closes the circuit together with at least one of the auxiliary resistors 500, 501, 502.
Even thought, the example of
An example safety interlock mechanism comprises:
In an example, the mechanism comprises a plurality of detection circuits connected to the plurality of interlock switches.
Also, the detection circuit may issue a detection signal to be communicated to a controller, the detection signal can be further used to prompt the user of an unsafe condition, to trigger an alert, and/or to trigger additional protection circuits.
In a further example, the actuator is mechanically coupled to a cover or a door. In this case, the unsafe condition may be that a door is open, i.e., the actuator is coupled to the door so that an open door does not activate the actuator and a closed door activates it.
As for the electronics, the detection circuit may comprise a transistor in a switch configuration. For example, the transistor may be a PNP bipolar junction transistor with a base-emitter connection and with the base connected to the interlock switch, the emitter connected to a supply source and the issuing a detection signal. In another example, the transistor may be a P-channel field effect transistor with a source-gate connection and with the gate connected to the interlock switch, the source connected to a supply source and the drain issuing a detection signal.
In the mechanism, the plurality of interlock switches may be serially connected by an intermediate node and the detection circuit may comprise a supply source with a voltage higher than a highest voltage of the intermediate node. For example, the supply source is a source with a voltage higher than 110% the highest voltage of the intermediate node.
An example printing system comprises a plurality of compartments with respective covers and a safety interlock mechanism comprising:
In an example, the compartments are selected from: printing agent storage, carriage, moving parts than can trap the operator, etc.
In a further example, the detection circuit is connected to each of the plurality of interlock switches.
The system may also comprise a controller to receive a detection signal from the detection circuit. The detection signal may be use as an alert or as a trigger to another circuit. Further, the controller may issue a prompt signal to the user when the detection circuit determines a change in the position of the actuator.
In an example, the detection circuit comprises a transistor in a switch configuration. The transistor may be, e.g., a transistor in a switch configuration.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/054269 | 9/29/2017 | WO | 00 |
