Safety switch and associated methods

Patent metadata

Field	Value
Publication number	US-9824841-B2
Application number	US-201514943650-A
Country	US
Kind code	B2
Filing date	Nov 17, 2015
Priority date	Nov 17, 2015
Publication date	Nov 21, 2017
Grant date	Nov 21, 2017

Abstract

A cable pull switch includes a polychotomous sensor configured to provide a reading of at least one of a plurality of values, the reading corresponding to a tension on a pull cable or a linear displacement of an end of a pull cable. A processing device is configured to receive the reading, determine whether a value of the reading is outside of a non-tripped value window, a limit edge being a pull threshold value, and responsively generate an output signal indicative of a cable pull event. Other features and improvements are described.

First claim

What is claimed is:

1. An apparatus comprising:
a cable pull switch including:
a substrate configured to couple to a first end of a pull cable and configured to experience a variable mechanical stress related to a tension exerted by the pull cable;
an electrical strain gauge bonded to the substrate and configured to alter an electrical resistance through the strain gauge in proportion to the variable mechanical stress experienced by the substrate; and
at least one processing device coupled to the strain gauge, the processing device configured to:
receive an indication of the value of the electrical resistance through the strain gauge;
determine whether the value of the electrical resistance through the strain gauge exceeds an upper pull threshold value, the upper pull threshold value being indicative of a cable pull event; and
generate an output signal indicative of the cable pull event in response to determining that the electrical resistance through the strain gauge exceeds the upper pull threshold value;

wherein the at least one processing device is further configured to:
determine a rate of change of the value of the electrical resistance through the strain gauge; and
adjust the upper pull threshold value dependent upon the rate of change of the value of the electrical resistance through the strain gauge.

2. The apparatus of claim 1 wherein the at least one processing device is further configured to:
determine whether the value of the electrical resistance through the strain gauge is below a lower slack threshold value, the lower slack threshold value indicative of a cable slack event; and
generate an output signal indicative of the cable slack event in response to determining that the electrical resistance through the strain gauge is below the lower slack threshold value.

3. The apparatus of claim 2 wherein the at least one processing device is further configured to:
determine whether the value of the electrical resistance through the strain gauge is below a lower slack adjustment margin threshold value, the lower slack adjustment margin threshold value being greater than the lower slack value;
generate an output signal indicative of a requirement to increase the tension exerted by the pull cable in response to determining that the electrical resistance through the strain gauge is below the lower slack adjustment margin threshold value;
determine whether the value of the electrical resistance through the strain gauge is above an upper pull adjustment margin threshold value, the upper pull adjustment margin threshold value being less than the upper pull threshold value;
generate an output signal indicative of a requirement to decrease the tension exerted by the pull cable in response to determining that the electrical resistance through the strain gauge is below the lower slack adjustment margin threshold value.

4. The apparatus of claim 3 wherein the processing device is further configured to generate an output signal indicating that the tension exerted by the pull cable is acceptable in response to determining that the electrical resistance through the strain gauge is above the lower slack adjustment margin threshold value and that the electrical resistance through the strain gauge is above the lower slack adjustment margin threshold value.

5. The apparatus of claim 3 further comprising a at least one of a visual indicator or an audible indicator coupled to the at least one processing device and configured to output at least one of a visual indication or an audible indication corresponding to the output signal indicative of a requirement to at least one of increase or decrease the tension exerted by the pull cable.

6. The apparatus of claim 1 wherein the variable mechanical stress is proportionate to the stress exerted by the pull cable.

7. The apparatus of claim 1 wherein the substrate is a metal substrate.

8. The apparatus of claim 1 wherein the at least one processing device is further configured to:
lower the upper pull threshold value inversely proportional to the rate of change of the value of the electrical resistance through the strain gauge.

9. The apparatus of claim 1 wherein the at least one processing device is further configured to:
determine whether the rate of change of the value of the electrical resistance through the strain gauge is below a threshold rate of change value; and
adjust the upper pull threshold value to a new upper pull threshold value that is based on a present reading of the value of the electrical resistance through the strain gauge.

10. The apparatus of claim 1 further comprising:
a pull cable excitation module configured to:
couple to a second end of the pull cable;
enter a pull cable excitation state by varying a tension exerted on the second end of the pull cable; and
communicate with the cable pull switch to initiate the pull cable excitation state;

wherein the cable pull switch is configured to:
detect at the first end of the pull cable the varying tension exerted on the second end of the pull cable during the pull cable excitation state; and
generate an output signal indicative of a pull cable failure in response to failing to detect the varying tension during the pull cable excitation state.

11. The apparatus of claim 1 wherein the cable pull switch further comprises a spring loaded shaft coupled to the substrate, the spring loaded shaft configured to be coupled to the pull cable and to slide along a longitudinal axis of the shaft to translate a tension exerted by the pull cable to the substrate.

Assignees

• Rockwell Automation Tech Inc
• Rockwell Automation Tech Inc

Inventors

• Tsang Andrew L
• Sacherski Burt
• Tambeau Steven Robert
• Ananthanarayanan Arvind
• Dogul James Edward
• Bubar Todd

Classifications

• G08B13/122 Primary

  for a perimeter fence (features peculiar to electrified fences A01K3/00) · CPC title

• H03K2217/94026

  Automatic threshold calibration; e.g. threshold automatically adapts to ambient conditions or follows variation of input · CPC title

• H01H2239/052

  Strain gauge · CPC title

• H01H3/0226 Primary

  operated by a pull cord · CPC title

• H01H71/50 Primary

  Manual reset mechanisms {which may be also used for manual release} · CPC title