Safety switching device and method for failsafe shutdown of an electric load

• US 7,573,693 B2
• Filed: 11/16/2005
• Issued: 08/11/2009
• Est. Priority Date: 05/23/2003
• Status: Expired due to Fees

• Current Assignee: PILZ GmbH & Company
• Original Assignee: PILZ GmbH & Company
• Inventors: Hornung, Guenter
• Primary Examiner(s): PALADINI, ALBERT WILLIAM
• Application Number:
  US11/280,637
• Publication Number:
  US 20060077613A1
• Time in Patent Office: 1,364 Days
• Field of Search: 361/111, 361/118, 361/119
• US Class Current: 361/111
• CPC Class Codes: H01H 47/004 using plural redundant serial connected relay operated contacts in controlled circuit
• CPC Class Codes: H02H 9/047 Free-wheeling circuits

Abstract

The invention relates to a safety switching device for the failsafe shutdown of an electric load, such as an electrically driven machine. The safety switching device has a signal processing part for receiving and evaluating an input-side switching signal, which, for example, originates from an emergency stop switch. It also has at least one switching element which, controlled by the signal processing part, provides an output-side switching signal for shutting down the load. An anti-surge element is provided for canceling reaction voltage spikes when the load is shut down. The anti-surge element has at least a first and a second anti-surge operating mode, which can be activated as an alternative to one another.

Claims

1. A safety switching device for failsafe shutdown of an electric load in response to an input-side switching signal provided from a safety transmitter, the safety switching device comprising:

a signal processing part for receiving and evaluating the input-side switching signal from the safety transmitter,

at least one switching element adapted to provide an output-side switching signal for shutting down the load, the at least one switching element being controlled by the signal processing part in response to the input-side switching signal, and

at least one anti-surge element for canceling voltage spikes when the load is shut down,

wherein the anti-surge element has at least a first and a second anti-surge operating mode configured to be activated as an alternative to one another,

wherein the anti-surge element has a low response threshold in the first anti-surge operating mode and a high response threshold in the second anti-surge operating mode, and

wherein the anti-surge element is switched over from the first to the second anti-surge operating mode if the signal processing part triggers a safety shutdown by appropriately controlling the at least one switching element.

2. The safety switching device of claim 1, wherein the signal processing part is configured to select between the first and the second anti-surge operating mode.

3. The safety switching device of claim 1, wherein the signal processing part has a first operating state, during which the load is switched on, and a second operating state for shutting down the load.

4. The safety switching device of claim 3, wherein the anti-surge element is in the first anti-surge operating mode during the first operating state, and it is in the second anti-surge operating mode during the second operating state.

5. The safety switching device of claim 3, wherein the signal processing part is designed, in its first operating state, to switch off the at least one switching element in a continuing pulsed manner.

6. The safety switching device of claim 1, further comprising an overvoltage protection element which is arranged in parallel to the at least one switching element.

7. The safety switching device of claim 6, wherein the anti-surge element has a low response threshold in the first anti-surge operating mode and a high response threshold in the second anti-surge operating mode, and wherein the overvoltage protection element has a third response threshold, which is higher than the low response threshold of the anti-surge element.

8. The safety switching device of claim 1, wherein the anti-surge element comprises a switchable semiconductor component as an anti-surge component.

9. The safety switching device of claim 7, wherein the switchable semiconductor component is a thyristor.

10. The safety switching device of claim 7, wherein the switchable semiconductor component is integrated in the safety switching device.

11. The safety switching device of claim 1, wherein the at least one switching element is a semiconductor switching element.

13. The safety switching device of claim 1, wherein the safety transmitter is at least one of an emergency stop button, a guard door, a light barrier arrangement and two-handed control switches.

12. A method for failsafe shutdown of an electric load in response to an input-side switching signal provided from a safety transmitter, comprising the steps of:

receiving and evaluating the input-side switching signal from the safety transmitter,

shutting down the load as a function of the input-side switching signal, and

canceling voltage spikes by means of an anti-surge element when the load is being shut down,

wherein the anti-surge element has at least a first and a second anti-surge operating mode, which are activated as an alternative to one another,

wherein the anti-surge element has a low response threshold in the first anti-surge operating mode and a high response threshold in the second anti-surge operating mode, and

wherein the anti-surge element is switched over from the first to the second anti-surge operating mode when the load is being shut down.

14. A safety switching device for failsafe shutdown of an electric load, the safety switching device comprising:

a signal processing part for receiving and evaluating an input-side switching signal,

at least one switching element adapted to provide an output-side switching signal for shutting down the load, the at least one switching element being controlled by the signal processing part, and

at least one anti-surge element for canceling voltage spikes when the load is shut down, and

an overvoltage protection element arranged in parallel to the at least one switching element,

wherein the anti-surge element has at least a first and a second anti-surge operating mode configured to be activated as an alternative to one another,

wherein the anti-surge element has a low response threshold in the first anti-surge operating mode and a high response threshold in the second anti-surge operating mode, and

wherein the overvoltage protection element has a third response threshold, which is higher than the low response threshold in the first anti-surge operating mode but lower than the high response threshold in the second anti-surge operating mode.