Safety switch and associated methods

Patent metadata

Field	Value
Publication number	US-10304648-B2
Application number	US-201715815087-A
Country	US
Kind code	B2
Filing date	Nov 16, 2017
Priority date	Nov 17, 2015
Publication date	May 28, 2019
Grant date	May 28, 2019

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 processor coupled to the polychotomous cable pull sensor configured to determine a rate of change of the value of the reading from the sensor and determine an occurrence of a cable pull event, the determination based on the determined rate of change of the value, and determine whether the rate of change of the value of an electrical resistance through the polychotomous cable pull sensor is below a threshold rate of change value, and adjust an 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.

First claim

What is claimed is:

1. A cable pull switch comprising:
a polychotomous cable pull sensor configured to provide a reading comprising at least one of a plurality of values, the reading corresponding to at least one of a tension on a pull cable or a linear displacement of a first end of a cable;
at least one processor coupled to the polychotomous cable pull sensor, the processor configured to:
determine a rate of change of the value of the reading from the sensor;
determine an occurrence of a cable pull event, the determination based at least in part on the determined rate of change of the value;
continuously monitor the reading;
periodically adjust an upper pull threshold value at a fixed interval of time if the rate of change of the value of the reading from the sensor is below a rate of change threshold; and
periodically adjust a lower slack threshold value at the fixed interval of time if the rate of change of the value of the reading from the sensor is below a rate of change threshold.

2. The cable pull switch of claim 1 , wherein the at least one processor is further configured to:
determine whether the rate of change of the value of an electrical resistance through the polychotomous cable pull sensor is below a threshold rate of change value; and
adjust an 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 polychotomous cable pull sensor.

3. The cable pull switch of claim 1 , wherein the at least one processor is further configured to:
determine whether the reading 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 reading is below the lower slack threshold value.

4. The cable pull switch 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.

5. The cable pull switch of claim 1 further comprising:
a substrate configured to couple to a first end of the pull cable and configured to experience a variable mechanical stress related to a tension exerted by the pull cable; and
an electrical strain gauge bonded to the substrate and configured to alter an electrical resistance through the electrical strain gauge in proportion to the variable mechanical stress experienced by the substrate.

6. The cable pull switch of claim 5 further comprising:
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.

7. The cable pull switch of claim 5 , wherein the at least one processor is further configured to:
receive an indication of the value of the electrical resistance through the electrical strain gauge;
determine whether the value of the electrical resistance through the electrical 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 electrical strain gauge exceeds the upper pull threshold value.

8. The cable pull switch of claim 5 , wherein the at least one processor is further configured to:
determine whether the value of the electrical resistance through the electrical 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 electrical strain gauge is below the lower slack threshold value.

9. The cable pull switch of claim 5 , wherein the variable mechanical stress is proportionate to the stress exerted by the pull cable.

10. The cable pull switch of claim 5 , wherein the substrate is a metal substrate.

11. A cable pull switch comprising:
a polychotomous cable pull sensor configured to provide a reading comprising at least one of a plurality of values, the reading corresponding to at least one of a tension on a pull cable or a linear displacement of a first end of a pull cable;
at least one processing device coupled to the cable pull sensor, the processing device configured to:
receive the reading from cable pull sensor;
determine whether a value of the reading is outside of a non-tripped value window, a first limit edge side of the non-tripped value window comprising a pull threshold value, the pull threshold value being indicative of a cable pull event;
generate an output signal indicative of the cable pull event in response to determining that the value of the reading is outside of the non-tripped value window on the first limit edge side;
continuously monitor the reading;
determine a rate of change of the value of the reading from the sensor;
periodically adjust an upper pull threshold value at a fixed interval of time if the rate of change of the value of the reading from the sensor is below a rate of change threshold;
periodically adjust a lower slack threshold value at the fixed interval of time if the rate of change of the value of the reading from the sensor is below a rate of change threshold; and
determine an occurrence of a cable pull event, the determination based at least in part on the determined rate of change of the value.

12. The cable pull switch of claim 11 , wherein the at least one processing device is further configured to:
determine whether the value of the reading is outside of the non-tripped value window, a second limit edge side of the non-tripped value window comprising a slack threshold, the slack threshold indicative of a cable slack event; and
generate an output signal indicative of the cable slack event in response to determining that the value of the reading is outside of the non-tripped value window on the second limit edge side.

13. The cable pull switch of claim 11 , wherein the at least one processing device is further configured to:
determine whether the reading 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 reading is below the lower slack threshold value.

14. The cable pull switch of claim 11 , 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 f

Assignees

• 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

• H01H2239/052

  Strain gauge · CPC title

• H01H71/50 Primary

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

• G08B21/187

  Machine fault alarms · CPC title

• H03K2217/94026

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