Electricity: electrical systems and devices – Control circuits for electromagnetic devices – For relays or solenoids
Patent
1996-11-05
1998-10-06
Gaffin, Jeffrey A.
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
For relays or solenoids
361 78, H01H 4728
Patent
active
058186816
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an electromagnetic relay drive circuit for driving an electromagnetic relay fitted to a control circuit, which takes safety into consideration. In particular, the present invention relates to a fail-safe electromagnetic relay drive circuit which takes into consideration faults due to fusing of the electromagnetic relay contact points.
BACKGROUND ART
In general, it is necessary with drive control systems for machines where safety is of concern, that the configuration to be such that a high energy output indicating safety is received when, for example, a movable region of a machine is in a safe condition (a safe condition even if the machine is operating). This is because with a control system wherein a high energy output is received when the movable region of the machine is in a danger condition (a danger condition when the machine is operating), then if a fault occurs in the constituent elements of the control system so that the high energy output ceases to be produced, or the generated high energy output is not received, then since no high energy output is received, a safe condition is judged and control for the safe condition (control for operation of the machine) is carried out, even though the movable region of the machine may be in a dangerous condition. On the other hand, with a control system configured such that a high energy output is received when the movable region of the machine is in a safe condition, then even if the high energy output ceases due to a fault in the constituent elements of the system, since non receipt of a high energy output has the meaning of a danger condition, then the danger condition cannot be mistaken for a safe condition, as with the beforementioned arrangement. Therefore, when safety information is represented by two values with a logic value of "1" for the safe condition and a logic value of "0" for the unsafe condition, the logic value of "1" must be transmitted as a high energy condition, and the logic value of "0" as a low energy condition or zero. For example, in the case where the release of a brake is carried out at the time of safety to thereby start the operation of a movable portion of a machine, at this time the energy for brake release must be a high energy condition meaning safety. This way of thinking is disclosed for example in U.S. Pat. No. 5,345,138.
With drive control systems for machines wherein safety is of concern, an electromagnetic relay is often used. In this case, the construction is such that when the movable region of the machine is in a safe condition, a high energy condition output indicating safety is received, thus switching on the make contact points of the electromagnetic relay to enable operation of the machine.
For example, with an electromagnetic relay drive circuit wherein safety information output from a sending side, is transmitted in a high energy condition to a receiving side electromagnetic relay via external line terminals to thereby advise of a safe condition, then a high energy output is generated from the sending side when safety is indicated by the safety information, and when the remote receiving side electromagnetic relay connected by an external line portion via the external line terminals is thus excited so that the make contact points comes on, a safe condition is indicated, and for example, an operation permit signal is output for a movable portion of a machine.
However, in the case where an electromagnetic relay is used in the transmission of safety information, faults such as fusing of the relay contact points must be carefully considered. A construction is therefore required which can check for the presence of contact point fusion in the electromagnetic relay, and output an operation permit signal for the movable portion of a machine only when there is no contact point fusion and the movable region of the machine is in a safe condition, and which does not err on the danger side, even in the event of contact point fusion.
Moreover, to make a fail-safe circuit con
REFERENCES:
patent: 4291359 (1981-09-01), Dieterle
patent: 4661880 (1987-04-01), Futsuhara
patent: 5027114 (1991-06-01), Kawashima et al.
patent: 5345138 (1994-09-01), Mukaidono et al.
patent: 5559664 (1996-09-01), Dogul et al.
Futsuhara Koichi
Sakai Masayoshi
Gaffin Jeffrey A.
Medley Sally C.
The Nippon Signal Co. Ltd.
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