Friday, January 7, 2011

System and method for measuring winch line pull

Various types of winches are used in conjunction with mobile lift devices to engage and support loads in a wide variety of environments. The primary purpose of many mobile lift devices is to move a load from a first position to a secondposition, whether by sliding or lifting the load. In particular, mobile lift devices may be used for hoisting, towing, and/or manipulating a load, such as a disabled vehicle, a container, or any other type of load. Mobile lift devices incorporating aload moving device, such as wreckers having a rotatable boom assembly, generally include devices for stabilizing the mobile lift device during operation of the load moving device. In using a winch in conjunction with a mobile lift device, it istypically useful to monitor the line pull of the winch while manipulating the load. However, in certain cases, it is difficult to determine the line pull of a winch when multiple winches are being used to manipulate the load (e.g., one winch is beingused to tie-off the load moving device and another winch is being used to recover the load). It would be advantageous to develop a monitoring system for determining a line pull of a winch when the load moving device is engaging a load.

Accordingly, there is a need for an improved mobile lift device having a monitoring system for monitoring the line pull of a winch. There is also a need for an improved mobile lift device having one or more sensors coupled to a monitoringsystem, in order to generate a signal representative of a torque generated by a motor of the winch, in order to retract the cable onto a drum of the winch. There is also a need for an improved mobile lift device having one or more sensors coupled to amonitoring system, in order to generate a signal representative of a number of layers of the cable retracted onto the drum, wherein a layer of the cable is formed by a single wrap of the cable onto the drum. There is also a need for an improved mobilelift device having a load moving device with one or more sheaves supported at the distal end of the load moving rotatable in at least two axis. There is also a need for an improved mobile lift device having a load moving device that is coupled to arotator to permit the load moving device to rotate about at least two axis relative to the mobile lift device.

One embodiment of the invention pertains to a control system for determining a line pull of a winch. The system comprises a first sensor configured to measure a torque generated by the winch to retract a cable and a second sensor configured tomeasure a number of layers of the cable retracted by the winch, wherein a layer of the cable is formed by a single wrap of the cable onto a container. The system further comprises a monitoring circuit coupled to the first and second sensors, wherein themonitoring circuit is configured to determine the line pull of the winch based on the torque generated by the winch and the number of layers of cable retracted onto the container.

Another embodiment of the invention pertains a method for determining a line pull of a winch, such that the winch includes a motor and a drum coupled to the motor. The steps of the method comprise calculating a torque generated by the motor ofthe winch, measuring a number of layers of a cable retracted by the winch onto a container, wherein the retracting of the cable creates one or more layers of the cable on the container; and determining the line pull of the winch based on the torque andthe number of layers of the cable retracted onto the container.

Another embodiment of the invention pertains a method for determining a line pull of a winch, the winch including a drum and a motor, such that the winch is coupled to a cable, wherein the cable is configured to retract onto the drum, creatingone or more layers of cable on the drum. The motor of the winch is configured to generate a torque to manipulate a load via the cable. The steps of the method comprise measuring the torque generated by the motor to manipulate the load and calculating aforce based on the measured torque. The steps further comprise determining a number of layers of the cable retracted onto the drum, wherein a layer of the cable is formed by a single wrap of the cable onto the drum, and calculating a cable radius of thenumber of layers of cable retracted onto the drum. The steps further comprise determining the line pull of the winch based on the measured torque generated by the motor and the cable radius, and displaying the line pull to an output device.

Another embodiment of the invention pertains to a mobile lift device, comprising a chassis for movement over a surface, a rotator supported by the chassis, a boom coupled to the rotator to permit the boom to pivot about at least two axes relativeto the chassis, and a first sheave supported at the distal end of the boom, wherein the sheave rotatably supported to rotate about at least two axes relative to the boom. The device further comprises a first winch supported at the rotator, the winchincluding a motor for and a drum couple to the motor and a cable supported by the first winch and the first sheave. The device further comprises a first sensor configured to measure a torque generated by the motor to retract the cable onto the drum anda second sensor configured to measure a number of layers of the cable retracted onto the drum, wherein a layer of the cable is formed by a single wrap of the cable onto the drum. The device further comprises a monitoring circuit coupled to the first andsecond sensors, the monitoring circuit being configured to calculate the line pull of the winch based on the torque generated by the motor and the number of layers of cable retracted onto the drum.

Another embodiment of the invention pertains to a monitoring system for determining a line pull of a winch coupled to a load moving device. The winch has at least one cable attached to a load to lift or slide the load, wherein the winch includesa motor for generating a torque and a drum coupled to the motor to house the cable. The system comprises a first sensor configured to generate a first signal representative of the torque generated by the motor to retract the cable onto the drum and asecond sensor configured to generate a second signal representative of a number of layers of the cable retracted onto the drum, wherein a layer of the cable is formed by a single wrap of the cable onto the drum. The system further comprises a monitoringcircuit coupled to the first and second sensors, wherein the monitoring circuit is configured to determine the line pull of the winch based on the generated force and a cable radius, such that the cable radius is calculated by the radius of the number oflayers of cable retracted onto the drum.

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