Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B66—HOISTING; LIFTING; HAULING
  • B66D—CAPSTANS; WINCHES; TACKLES, e.g. PULLEY BLOCKS; HOISTS
  • B66D1/00—Rope, cable, or chain winding mechanisms; Capstans
  • B66D1/54—Safety gear
  • B66D1/58—Safety gear responsive to excess of load
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B66—HOISTING; LIFTING; HAULING
  • B66B—ELEVATORS; ESCALATORS OR MOVING WALKWAYS
  • B66B5/00—Applications of checking, fault-correcting, or safety devices in elevators
  • B66B5/02—Applications of checking, fault-correcting, or safety devices in elevators responsive to abnormal operating conditions
  • B66B5/14—Applications of checking, fault-correcting, or safety devices in elevators responsive to abnormal operating conditions in case of excessive loads
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B66—HOISTING; LIFTING; HAULING
  • B66D—CAPSTANS; WINCHES; TACKLES, e.g. PULLEY BLOCKS; HOISTS
  • B66D1/00—Rope, cable, or chain winding mechanisms; Capstans
  • B66D1/28—Other constructional details
  • B66D1/40—Control devices
  • B66D1/42—Control devices non-automatic
  • B66D1/46—Control devices non-automatic electric
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
  • G01L5/0061—Force sensors associated with industrial machines or actuators
  • G01L5/0071—Specific indicating arrangements, e.g. of overload
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
  • H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
  • H02H7/085—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors against excessive load

Definitions

• the present invention relates to a method of and a device for indicating overload and interrupting the lifting of an overload when a hoist is used that is driven by an asynchronous induction motor.
• the work loads are hooked on to a lifting hook or similar device. Via one or more wire ropes, the hook will then be connected to a winding drum, driven by an induction motor. Between the winding drum and the induction motor may be gear mechanisms in order to adapt suitable motor revolutions per minute to convenient lifting speed. The load will be lifted when the wire is wound on the winding drum and vice versa.
• the induction motor may advantageously be provided with slip rings connected to fixed or variable resistances. The purpose of this is to get a smooth starting of the lifting and to limit the starting currents of the motor.
• the hoist is dimensioned for the rated work load.
• the hoisting apparatus comprises a slip-ring induction motor 1 with its stator winding 2 connected to a feeder cable 3 via a switch 13 and a power meter 7.
• the rotor gap of the induction motor is denoted by numeral 9.
• An instrument transformer 8 is connected for measuring the rotor frequency.
• a power meter 7, the instrument transformer 8 and a switch 13 are connected to a computer 5.
• the hoist is provided with a winding drum 6, a lifting wire 11 and a lifting hook 12 in which a load 10 is suspended.
• the input power P 1 of the induction motor 1 is transmitted to the stator winding 2 via the feeder cable 3.
• the power may be divided up into two parts, namely P 2 and P 2 - 4 ⁇ P 2 indicates the copper losses appearing in the stator winding 2 and may be considered to be constant within the actual working range.
• P 2-4 indicates the power transmitted between stator 2 and rotor 4.
• T m is the torque of the by motor 1.
• Equations (1) and (2) have been taken from the book "Elektriska maskiner” by Karl Erik Hallenius, 2nd Edition, Malmö, Liber laromedel 1977, PP 10:38 - 10:81.
• Equation (3) has been taken from the book "TEFYMA; Handbok for grundlaggande teknisk fysik, fysik och matematik” by Ingelstam-Rönngren-Sjöberg, Sjöbergs förlag, Sweden/Bromma 1984, p 69.
• the revolutions per minute, ⁇ may be established anywhere within the system by means of a suitable measuring device. According to the figure, an instrument transformer 8 is used that measures the revolutions per minute by measuring the rotor circuit frequency which is proportional to the speed of rotation. In computer 5, the frequency amount will be converted into an amount of speed of rotation ⁇ .
• Equations (1) to (3) result in:
• T L K P 1 - A - B ⁇ (6)
• K, A, and B are constants.
• T L (Mx +Mo) (a + g) ⁇ r (7) l ⁇ h&xe.
• M x weight of work load 10
• Mo the weight of other parts suspended from the winding drum 6, such as wire 11, hook 12 etc;
• g the acceleration due to gravity
• a the instantaneous acceleration of the work load, and
• r the imaginary radius experienced by the motor.
• the force F x exerted on the hoisting machinery is
• the hook loading F x K 1 ⁇ P 1 - A 1 - B 1 ⁇ , (10) the hook loading F x may be calculated when knowing constants K 1 , P 1 and A 1 , i.e. the hook loading may be estimated, Hook K 1 , P 1 and A 1 , i.e. the hook loading may be estimated.
• Hook loading F x consists of the real load 10 plus the dynamic addition of the load, but in this application, the dynamic addition is small as compared with the real load 10.
• the rotor was provided with 4 resistances 9 connected in series, which we could uncouple in 5 steps.
• the values were also entered into Diagram 1 with load 10 along the horizontal axis and the power along the vertical axis. According to the diagram, the power without work load amounted to 29.12 kW, and the power is directly proportiona to the load weight 10. If these values are put into equation 10 above, the constants K 1 and A 1 will be defined as 6.3 and 183 resp. B.
• the power input at the known work load of 15.6 tons, we measured the power input at 3 different regulating steps with 2, 1 and 0 resistances, 9, respectively, switched into the rotor circuit.
• the power input (kW) on the vertical and the time (seconds) when measuring, will be clear from diagram 2. It can be seen that the power input on step 1 amounts to about 54 kW at a constant lifting speed.
• Diagram 3 drawn by the computer and showing the power on the vertical and time on the horizonal: a) a short current peak appeared just when starting. b) a shorter period with constant power occured due to the fact that the hoist brake was not yet released. c) A period of about 4 seconds with falling power followed; then the power stabilized. According to continued testing, the lifting speed was stabilized to constant speed at the same time. D. Diagram 4 shows a corresponding hoisting of the work load of 10.5 tons.
• Diagram 5 shows the rotor current as a function of time from start-up until having stabilized at a minimum value.
• the time between two currents peaks increased; accordingly, the slip between the angular velocity of rotor 4 and the synchronous angular velocity of motor 1 decreased.
• the slip S was analyzed the variations of the current.
• the slip S indicated as the synchronous rpm ⁇ s minus the actual rpm ⁇ , divided by the synchronous rpm accordingly
• Diagram 6 shows the power input as a function of time from start-up on the one hand and the slip at corresponding times on the other. It is clear that the angular velocity of the rotor nears a constant value; accordingly, the angular velocity increases asymptotically from zero at start when starting.
• the interferences at the end are due to the fact, that we are dividing by a small value.
• the acceleration nears asymptotically zero.
• an overload protecting device can be obtained which will stand up to most standards, and which may be adapted to different standards by a simple reprogramming of the computer. If a standard prescribes that overload may appear, however, only during a predetermined period for example 0.5 seconds, the computer can be programmed to initiate the switching off of the motor's supply current, provided that all calculations during such a period indicate overload. The time concerned is usually 0.2 - 1.0 seconds, and at least three calculations should be done during the period. Alternatively the computer can be programmed to initiate switching-off when a preset number of calculations have estimated overload, provided-that at least this number of calculations are made during the predefined period of time.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Control And Safety Of Cranes (AREA)
• Jib Cranes (AREA)
• Amplifiers (AREA)
• Control Of Eletrric Generators (AREA)
• Heat Treatment Of Steel (AREA)
• Control Of Electric Motors In General (AREA)

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Publications (1)

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Cited By (1)

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Citations (4)

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• 1986
  • 1986-09-26 SE SE8604084A patent/SE454625B/sv not_active IP Right Cessation
• 1987
  • 1987-09-25 EP EP87906477A patent/EP0402353A1/en not_active Withdrawn
  • 1987-09-25 US US07/358,367 patent/US5039028A/en not_active Expired - Fee Related
  • 1987-09-25 AU AU80238/87A patent/AU8023887A/en not_active Abandoned
  • 1987-09-25 WO PCT/SE1987/000433 patent/WO1988002478A1/en not_active Application Discontinuation
• 1988
  • 1988-05-24 DK DK281988A patent/DK281988A/da not_active Application Discontinuation

Patent Citations (4)

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