This new patent (US Pat. No. 7,063,306) cites two previous patents with crane and winch control systems, but states that these systems do not provide all the features sometimes desired for the safe and efficient operation of a winch. The new electronic winch monitoring system is claimed to overcome the disadvantages of conventional systems.
How it works
In the aspect first described, the winch’s fixed-ratio, reduction gearbox (316) connects the input and output shafts of the winch drive, with a primary brake (315) of interleaved friction and spacer plates connected to the input shaft.
The input shaft is driven by a hydraulic motor powered by a pump with any prime mover. The pump and motor will be typically of the variable displacement type, with a motor control unit regulating the speed, torque and direction of the motor. The two may be connected in closed or open circuit as required. The winch drum (302) is connected to the output shaft for bi-directional operation. It carries a suitable length of wire rope wound onto the drum in concentric layers.
An auxiliary brake (314) of similar design to the primary brake, but larger, is connected to the output shaft. This is normally of a fail-safe type, requiring hydraulic power to release it. The monitoring assembly is equipped with the necessary sensors (306, 308, 310, 312, etc) to provide signals to the monitoring system, which, in turn provides the required output to the brake control section and any data logging or display equipment.
The monitoring system in Fig 1 comprises an electronic control unit (304 – ECU), a system pressure sensor on the drive motor, an input speed sensor (306), an oil data sensor on the primary drive gearbox, an output speed sensor (308) and a rope layer sensor (310).
The ECU includes a programmable memory unit for storing instructions and data, a processor unit for executing instructions from the memory unit to which this is connected, and one or more input ports connected to the processor and leads to external sensors at the auxiliary brake, motor control unit and other devices. The ECU can be interfaced with a computer for programming and data transfer.
There is a system pressure sensor at the inlet to the hydraulic motor. The pressure will normally be proportional to the load on the winch drum. Typically the input and output speed sensors at the motor or input shaft, and output shaft respectively, are of magnetic (Hall-effect) type but other types can be used. An oil data sensor in the drive gearbox measure the lubricating oil temperature and/or the oil quality, also sending data signals to the ECU.
Fig 2 shows the detail of the winch drum and rope layer sensor. This enables the moment arm of the winch mechanism, or the effective winch radius (RE), to be known. It is the sum of the drum radius (RH) and the changing radial thickness of the rope layers (RR). The rope layer sensor (56) enables RR to be measured by measuring DR. That shown is an ultrasonic device, but other types can be used. The ECU can then calculate the effective winch radius within one rope width. More sensors can be used for greater accuracy.
Functions
The electronic winch monitor (EWM) can carry various monitoring and control duties including:
– Gear Train Monitoring
The ECU of the EWM can compare the actual input/output speed ratio with the previously known ratio. If it is not within a preset range, the ECU will send brake actuation signals to the auxiliary brake circuit, reducing the hydraulic pressure to close the brake, using a non-linear pressure-time profile (Fig 3) in some designs. It can also send a signal to the winch operator to indicate a fault, possibly with the gearbox.
– Drum Over-speed Monitoring
Similarly the ECU can compare the output speed with a preset maximum allowable value. If the actual speed exceeds this stored value then the ECU will signal to auxiliary winch brake to operate and indicate a fault to the operator.
– Minimum Rope Indication
The ECU will initiate the same actions if the signal or signals from the rope layer sensor show that a preset minimum number of rope layers on the drum have been reached
– Dynamic System Monitoring
The ECU can convert the signals from the various sensors previously mentioned into standardised unit, which can be sent to the operator display or a PC for viewing and/or logging.
– Winch Duty Cycle Histogram
The ECU monitors and stores data on the winch system speeds, hydraulic system pressure and the operating hours. This data can be displayed on a histogram on the display so that the operator or technician can determine the severity and duration of winch operation, including peak operating parameters.
– Constant Speed/Constant Load Operation
Using relevant sensor signals the ECU can calculate the load (for example, the pull) on the rope and the rope speed. If these are required to be constant, the ECU can send motor control signals to change the motor displacement and/or speed accordingly.
– Winch Data Storage
The memory unit of the ECU can store data, including winch manufacturer’s information, to be accessed by winch service personnel.
– Winch Service Interval Data
The sensor signals can enable the ECU to determine how often servicing of the winch is required based on the operating hours, severity of the duty cycle and/or monitored gear oil temperature and contamination levels.
– Safer Braking
The auxiliary winch brake is designed to stop and hold the load in case of gearing failure, failure of the primary brake, or loss of hydraulic braking. As well as being able to hold the full rated static load, it can further stop dynamic loads within the designed torque and energy limits. The auxiliary brake is therefore totally independent, and redundant to, any braking action from the primary brake or hydraulic drive.
In some circumstances the load being braked will be much less than the full hoist capacity, resulting in high G-forces when the brake is applied quickly. Such an application are man-baskets used in offshore installations (Fig 1 – 320). Conventional brakes may be difficult for the operator to modulate precisely by manual means with an on-off switch, possibly resulting in either dangerous G-forces from sudden braking on the personnel being carried, or impact on the surface below from insufficient braking. Conventional systems may employ hydraulic line orifices to attempt to control severe brake applications, but the inventors claim improved performance by the EWM system.
The EWM may be equipped to electronically control a pressure and/or flow from a solenoid valve (312) to give a predetermined and repeatable modulated hydraulic pressure signal to release and reapply the auxiliary brake. It can be further adapted to sense the operational parameters of the winch and ‘memorise’ the data so that, should a failure occur, the conditions just prior to the failure will be known.
The EWM can be programmed to apply the auxiliary brake automatically to provide a controlled and planned stopping distance based on the stored conditions data, so that the maximum accelerations on the load are limited and personnel in the man-basket will not be injured or thrown off.
It can also limit the stopping distance to a reasonable amount expected to be available, or according to a pre-programmed, derived and tested equation or matrix of values. Thus the winch can be successfully and optimally applied to a much broader range of loads, speeds and direction of operation. This not only optimises the conditions for man-basket operation, but extends a more controlled application to bigger loads and speeds.
Fig 3 shows the graph of a suitable non-linear pressure versus time profile for the hydraulic pressure in the auxiliary brake release circuit, and also a graph of the current control versus time for the brake control valve.
The overall profile of pressure versus time has two distinct sections. Before fault indication (section 902), the current supplied to the hydraulic circuit proportional valve is at a maximum (Imax), as is the pressure in the hydraulic brake release circuit (pmax).
Fault indication is received at time to. This is the start of the first section of the predetermined profile 904. It can be seen that, while the control current curve drops immediately, the hydraulic pressure curve may have a time lag due to circuit flow characteristics. Prototype experiments have shown the values of tI to be 0-80 ms.
The control unit then initiates the second section of the profile designated 906. This is the ‘ramp’ section within which the current is reduced gradually, allowing the hydraulic pressure to track it closely. At time tf the brake control current and brake release circuit pressure remain constant, and the auxiliary brake piston is fully retracted, as the brake is applying its full pressure. In prototypes experiments the ramp times are within the range 1500-5000ms, being well suited to minimising G-forces.
The patent discloses equations as one method of calculating the optimum ramp times for specific winching conditions. It is believed that suitable equations will provide a load velocity versus distance with a substantially parabolic profile.
Fault treatment
In the event of an indicated fault, the EWM can also be used to determine whether there has been a true gear train failure or a ‘false positive’ indication, prior to returning the winch control to the operator. The variation in speed ratio used for fault detection would indicate a discontinuity between the movement of the input and output shafts through the gears. A diagnostic subsystem will preferably take control of the winch upon fault indication so that control is not passed back to the operator until a series of diagnostic tests have been run and passed. The results and tests will be logged for future reference.
In order to reduce the occurrence of ‘false positives’ the EWM signals a fault only when the value of the difference between the calculated speed ratio and the stored predetermined fixed ratio exceeds a predetermined acceptable range value. This allows for possible signal interference, measurement errors, etc. Data conditioning processes such as simple sampling windows and averaging sampling windows based on time periods may also be used to reduce ‘false positives’. The size of the time windows can also be varied dynamically in order to cater for the higher incidence of measurement errors that may occur during slower winch drum speeds.
Fig 4 shows an enlarged operator control console for the EWM including one of several possible ‘drop down’ windows (1116) on the display and input/output control panel 1102. It includes context-sensitive (programmable) touch-screen buttons (1103) for operator control and information functions. The console also includes an array of indicator lights (1104) and hard-wired switches (1106 and 1108).
The ‘drop down’ screen shown provides the operator with information regarding the fault and instructions for further action. This happens in the case of a gear train fault indication causing the EWM to automatically take control from the operator and stop the winch. Other display screens that can be provided include those instructing the operator to perform diagnostic tests of the winch following a gear train fault indication. The patent includes a full description with a flow chart of the winch diagnostic subsystem.
About the patent
This article is an edited version of US patent 7,018,159. The inventors are Mark E Sanders of Broken Arrow, Oklahoma and David E Johnson of Coweta, Oklahoma. The assignee is PACCAR Inc. headquartered in Bellevue, Washington State, the Winch Division of which has plants in Broken Arrow and Okmulgee, Oklahoma.
Disclaimer
This article is an edited version of the patent and may omit legally or technically important text. To see the full patent go to www.hoistmagazine.com/patents
Marketing
The Winch Division of PACCAR Inc. manufactures planetary hoists, recovery and tractor winches, and utility truck products under the trade names of Braden, Carco and Gearmatic.
Designs referred to in the patent are being actively marketed as the EWM system and offered with the Braden CH Series of winches. In addition, the maintenance monitoring feature is being offered as an independent system known as the Braden Electronic Maintenance Modules or EMM. It can be ordered as an option on new winches or as a kit for retrofitting to any Braden Planetary Winch. The module mounted on the winch will show basic information, but more details can be downloaded to a PC.
