Slip sensing method and apparatus

Slip sensing means for sensing slip between an object and object supporting means having at least one supporting surface, said slip sensing means comprising

• thermal responsive means located at the supporting surface of the object supporting means and adapted for intimate engagement with the face of an object supported thereby,
• means for electrically heating said thermal responsive means to maintain the temperature thereof and the localized temperature of the object at the point of engagement therewith above ambient temperature, the temperature at the surface of the object decreasing with distance from the heated thermal responsive means, the temperature of the thermal responsive means at least momentarily changing with initial engagement thereof with the object and with slip of the object along the object supporting means after said initial engagement, and
• means for detecting change in the thermal responsive means in response to temperature change thereof due to slip of the object along the object supporting means for sensing said slip,
• said thermal responsive means comprising a thermistor,
• said means for electrically heating said thermistor comprising a resistor bridge, one arm of which bridge comprises said thermistor,
• a load resistor,
• a source of d.c. potential connected across one pair of opposed bridge junctions through said load resistor,
• operational amplifier means having a pair of input terminals connected across the other pair of opposed bridge junctions, and
• means for connecting the operational amplifier means output to the one bridge junction to which said thermistor and load resistor are connected, said thermistor providing a negative feedback path for said operational amplifier means.

A method of sensing slip between an object and object supporting means comprising,

• locating at least one thermal responsive element at the object supporting surface for intimate engagement with an object supported by the object supporting means,
• passing current through the thermal responsive element for heating the same to a temperature greater than ambient temperature and for localized heating of the object to substantially the temperature of the heated thermal responsive element, the temperature of the supported object decreasing toward ambient temperature with increased distance from the heated thermal responsive element,
• controlling current flow through the thermal responsive element to maintain the same at substantially constant temperature, and
• sensing changes in current flow through the thermal responsive element in response to change in temperature of the object at the heated thermal responsive element to provide an indication of relative slip between the object and the object supporting means.

A method of sensing slip between an object and object supporting means comprising,

• locating at least one thermal responsive element at the object supporting surface for intimate engagement with an object supported by the object supporting means,
• heating the thermal responsive element to a temperature greater than ambient temperature for localized heating of the object to substantially the temperature of the heated thermal responsive element, the temperature of the supported object decreasing toward ambient temperature with increased distance from the heated thermal responsive element,
• sensing temperature changes of the thermal responsive element to provide an indication of relative slip between the object and object supporting means,
• including said thermal responsive element in the negative feedback path of an operational amplifier and as one arm of a resistor bridge, input to the operational amplifier being obtained from one pair of opposed bridge terminals, and,
• supplying the other pair of opposed bridge junctions with a d.c. potential source through a load resistor, current flow through the load resistor being indicative of thermal responsive element temperature.

A method of sensing slip between an object and object supporting means comprising,

• locating at least one thermal responsive element at the object supporting surface for intimate engagement with an object supported by the object supporting means,
• heating the thermal responsive element to a temperature greater than ambient temperature for localized heating of the object to substantially the temperature of the heated thermal responsive element, the temperature of the supported object decreasing toward ambient temperature with increased distance from the heated thermal responsive element, and
• sensing temperature changes of the thermal responsive element to provide an indication of relative slip between the object and object supporting means,
• the step of heating the thermal responsive element includes controlling power to the thermal responsive element to maintain the same at a substantially constant temperature, and
• said step of sensing temperature changes of the thermal responsive element includes sensing changes in power supplied to the thermal responsive element to provide an indication of relative slip between the object and object supporting means.

A circuit arrangement for maintaining a thermistor at a substantially constant temperature and for sensing changes in resistance thereof for use in a slip detector, comprising

• a resistor bridge in which said thermistor comprises one arm of the bridge,
• a load resistor,
• a source of d.c. potential connected across one pair of opposed bridge junctions through said load resistor,
• an operational amplifier having a pair of input terminals connected across the other pair of opposed bridge junctions, and
• means for connecting the operational amplifier output to the one bridge junction to which said thermistor and load resistor are connected, the voltage across the load resistor being related to the temperature of the thermistor.