Patent Application
20160347592
The present invention relates generally to hoists, and more particularly, to hoists having a powertrain comprising a hysteresis clutch.
Hoists are used for lifting loads by means of chains, ropes or other pulling means. Such hoists are driven by a motor, in which case a transmission is provided between the pulling means and the motor.
It must be ensured that any overloading of the pulling means, the transmission or any other components of the hoist—even in the case of a faulty operating status such as, for example, a load being caught on an obstacle—does not result in any damage to the chain pulley block and, in particular, does not result in the dropping of the load. This applies, in particular, if the hoist is used in horizontal pulling operations, for example, in order to drive traversing gears or carriages.
To accomplish this, U.S. Pat. No. 3,573,518 describes a hoist with a powertrain consisting of a motor and a transmission and having a hysteresis clutch. The hysteresis clutch is accommodated in its own housing that is arranged in an extension of the motor housing. The hysteresis clutch is driven by the motor shaft and is itself connected to the input shaft of the transmission. The hysteresis clutch comprises a motor-driven rotor provided with permanent magnets and a disk arranged at a minimal distance from said rotor, said disk consisting of hysteretic magnetizable material. A disk-shaped air gap is formed. In addition, the disk is electrically conductive in order to generate slippage-induced vortices. A thermo-switch connected to the disk is disposed to stop the drive if a slippage occurring on the hysteresis clutch will not disappear after a short time. In doing so, the hysteresis clutch is adapted so that it permits a slippage only in the case of an overload and otherwise effects a non-torsional coupling between the two clutch halves. In addition, the clutch is only effective unidirectionally in upward direction. In opposite direction, the action of the hysteresis clutch is prevented by a freewheel arranged parallel to the hysteresis clutch. The freewheel is disposed to overcome the brake moment of a load pressure brake when the load is being lowered. The motor starting torque required therefor is greater than the torque for lifting the nominal load.
It is an object of the present invention to provide an improved hoist that has a torque limit at which a hysteresis clutch thereof begins to slip without mechanical friction. The torque of the slippage is smaller than the torque of the nominal load. In doing so, the torque of the nominal load is that moment of torsion that occurs on the clutch when the hoist lifts the nominal load, i.e., its maximum permitted load. In doing so, the slippage represents the difference between the rotational speeds of the two clutch halves, divided by the rotational speed of the motor-driven clutch half. Due to the slippage occurring before the load-bearing capacity is reached, the operation of the hoist can be improved in several respects.
When a load is lifted, in particular when it is lifted at a high lifting rate, a chain or an appropriate rope coupled with the load is initially slack. With a fast-moving drive, the latter becomes taut and lifts the load with a jolt. By providing a slippage of the hysteresis clutch before the pulling means builds up a pulling force corresponding to the nominal load, the load shock is cushioned considerably. Damaging reactions on the pulling means, the remainder of the powertrain or the supporting structure of the hoist of the crane system, or the like, are avoided or at least considerably reduced.
Setting the torque of the nominal load greater than the torque limit additionally allows a more intuitive handling of the hoist than before. In particular, when unknown or varying loads are being lifted, the subject hoist provides feedback regarding the size of the load to the operator in the course of daily practical operations. With a constant rotational speed of the motor that is to be driven, loads that are smaller than the nominal load but exceed the torque limit are lifted visibly slower than loads that are smaller than the maximum permitted load (with which the torque limit would be reached). Consequently, the operator perceives when the nominal load is being approached as a result of a noticeably slower lifting of the picked-up load.
Inasmuch as the hysteresis clutch exhibits a slippage already at a partial load that is clearly lower than the nominal load, a gentle startup of the hoist can be achieved even without the use of an inverter control of the motor. For example, the force of acceleration required for accelerating a suspended load in lifting direction causes the slippage to increase at the time the motor is switched on, so that the load can accelerate more slowly than the motor. This also applies to rotational speed reversals when the motor very rapidly changes its rotational speed and, for a time being, increased slippage in the hysteresis clutch allows reduced accelerations of the load and thus a minimization of the acting forces. A similar behavior can also be achieved when the motor is being switched off.
In particular, the hysteresis clutch allows the efficient absorption of vibrations due to the damping effect that is not a function of the rotational speed of said clutch. Such vibrations are triggered by switching the motor on and off, by rotational speed reversals or also by the polygon effect in chain pulleys (vibration triggering of the tensioned chain as a result of changing radii on the chain wheel). In this manner, it is possible to prevent that the load-bearing capacity is being exceeded due to the resonant vibrations of the chain and that a shutdown or other counter-measures are necessitated.
The torque limit at which the hysteresis clutch begins to develop a slippage different from zero can be set—appropriate for the purpose—for example, to at most to 0.95 times, 0.9 times, 0.8 times or to the nominal load torque or to another ratio thereto. The lower the torque limit is set, the more slippage is allowed by the hysteresis clutch during normal operation and the greater are the aforementioned effects.
Preferably, the hysteresis clutch features an increasing transmitted torque with increasing slippage. In doing so, it is ensured that torques above the torque limit can be transmitted. In this way, the hysteresis clutch can allow the lifting of loads that are minimally greater than the nominal load. The slippage may be up to 1 (i.e., 100%). Preferably, the force generated by the hoist at slippage 1 is within a tolerance range of forces that do not lead to any damage of the hoist or its supporting structures.
The hysteresis clutch can be designed to allow a longer period of operation at high slippage, without the motor being switched off. In this case, the hysteresis clutch provides a passive protection of the hoist and its supporting structure, in which case the forces limited by the hysteresis clutch may be trusted when dimensioning said hoist and said supporting structure. This allows the minimization of the otherwise to be implemented added safety features in dimensioning the system, without having to accept a reduction of safety.
The hysteresis clutch can be connected to a rotary speed detector. The latter comprises at least one means that is a function of the rotational speed and/or the rotary angle such as, e.g., a rotational speed sensor, a centrifugal switch, a resolver or the like. The rotational speed detecting means may be configured as an absolute value generator or an incremental generator. Preferably, the rotational speed detecting means is associated with at least the output-side clutch half in order to monitor said half in view of its rotational speed. Optionally, another rotational speed detecting means can detect and monitor the input-side clutch half. This rotational speed detecting means may also be installed in the motor. Rotational speed detecting means of any of the aforementioned designs will be generically referred to hereinafter as “rotational speed sensor”.
An analyzing device can compare the rotational speeds detected by the rotational speed sensors and determine, in particular, the rotational speed differences. The rotational speed difference (motor-side clutch rotational speed minus the transmission-side clutch rotational speed) divided by the motor-side clutch rotational speed represents the slippage. Preferably, the slope of the torque/slippage characteristic rises linearly. Above the torque limit, the detected slippage may be used as a measure for the force applied by the hoist. This also applies to non-linear torque/slippage relationships.
Referring to an advantageous embodiment, the hysteresis clutch is arranged in an oil bath. This oil bath can be part of the oil filling of the transmission or it may represent a separate oil volume. The hysteresis clutch may be arranged in the transmission housing. In both cases, the oil bath can be used efficiently for cooling the hysteresis clutch in that said bath absorbs the thermal energy generated on one clutch half and discharges it to the housing of the hoist in order to conduct the thermal energy into the environment. In particular, the hysteresis clutch may be in contact with an oil flow that is formed by the transmission oil. As a result of this, the energy transformed by the slippage into thermal energy can be discharged in such an efficient manner that the continuous operation of the hoist with slippage is made possible.
Preferably, the hysteresis clutch has a cylindrical design with a permanently magnetic rotor on the inside and a hollow cylindrical hysteresis ring on the outside, said ring potentially being subject to considerable heating during operation. By arranging said ring on the outside, simple and efficient cooling is possible.
The air gap of the hysteresis clutch may be free of oil or, if needed, also be filled with oil. In the latter case, the oil present in the air gap may result in an additional transmission of torque due to its viscosity and/or due to its hydrodynamic effects. It is possible to utilize the reduction of the oil viscosity concomitant with the heating of the oil in the air gap for the reduction of the torque transmission with an existing overload in order to keep the operator from further overloading the hoist.
Preferably, the hysteresis clutch has a size-adjustable air gap. Referring to a cylindrical air gap, an axial adjustment of at least one clutch half—with the radial air gap width remaining the same—can be used for the axial size reduction of said air gap width in order to adjust the torque limit as desired.
Referring to a hysteresis clutch having a conical air gap, an axial adjustment of at least one of the clutch halves can be used to adjust the air gap in view of its radial width, as well as its axial width, and its length, respectively. By adjusting the size of the air gap, it is possible to adjust or set the torque limit and/or the form and/or the slope of the torque/slippage characteristic.
An advantageous embodiment of the hoist has a powertrain comprising at least one brake, wherein at least one of the brakes is arranged on the transmission side, viewed from the hysteresis clutch. If the brake connected to the transmission is designed for a brake torque that is at least as great as the sum of the maximum load torque and the maximum torque that can be applied by the hysteresis clutch or the motor—depending on which is the lesser—a safety-oriented drive can be produced. The brake will be able to hold the load even if the motor is rotating uncontrolled in any direction, while the hysteresis clutch limits the transmitted torque to a value that can still be safely absorbed by the brake. Should such an error status continue to exist, the hysteresis clutch that operates mechanically in a contactless manner can reach a temperature at which one or more permanent magnets become weaker or demagnetize entirely. As a result of this, the torque transmission is attenuated or interrupted. Additional heating and dangerous overheating of the drive are thus prevented. This applies to hoists with thyristor-controlled drives, as well as to hoists with power mains-controlled drives.
This arrangement offers several advantages:
When an emergency switch is actuated, the brake stops the transmission and the pulling device. In the hysteresis clutch, the kinetic energy of the rotating motor is converted into thermal energy—without overloading the transmission or the clutch. This concept is particularly suitable for use in motors exhibiting a high rotational speed of more than 1500 or even more than 3000 revolutions per minute, these exhibiting a particularly high kinetic energy during operation.
Furthermore, this concept is suitable for safety-oriented drives. For example, if the motor is driven via an inverter that does not comply with the regulations for a safety-oriented inverter, the desired safety can still be achieved by the combination of brake and hysteresis clutch. This is true, in particular, when the maximum transmittable torque that is transmitted with a slippage of 1 and the torque due to the nominal load can be absorbed by the brake with sufficient safety.
In conjunction with a hysteresis clutch that is configured so as to be adjustable in view of its torque limit, there is the additional possibility of the controlled load lowering in an error situation. To accomplish this, the motor is blocked with a suitable tool or object so that it can no longer rotate. If a motor-side brake is provided, such brake may also be used to block the motor. Then the torque limit of the hysteresis clutch is slightly reduced by manual adjustment, and then the manual release of the transmission-side brake is tried. This is repeated until the torque limit has been reduced to a point at which the load is capable of at least slowly rotating the hysteresis clutch. Once this adjustment has been achieved, the transmission-side brake may be held manually released until the load has been deposited in a controlled manner on the ground or on another support. In doing so, an uncontrolled clutch slip of the load is excluded due to the positive slope of the torque/slippage characteristic.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings.
While the invention is susceptible of various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention.
Referring now more particularly to
The transmission 16 is a reduction gear 16 that transforms a high rate of revolutions of the motor into a low rate of revolutions of the pocket wheel 13 in order to raise and lower loads. Preferably, the transmission 16 is a non-self-locking toothed gearing. However, if needed, it may also comprise self-locking components such as a worm gear.
The powertrain 14 is connected to a transmission-side brake 17. Preferably, this may be a disk brake comprising a brake disk 18 that is associated with brake blocks 19, 20. Preferably, these are tensioned by the force of a spring 22 toward the brake disk 18. They may be released by one or more electromagnets 21 in order to free the brake disk 18.
As shown schematically in
Optionally, at least one of the clutch halves 24, 25 may be connected to a rotational speed sensor; in the simplest case, this is a centrifugal switch. Alternatively, it is also possible to connect both clutch halves 24, 25 to rotational speed sensors 27, 28, each generating a signal corresponding to the rotational speed of the clutch halves 24 and 25, respectively. The signals may be switching signals, analog signals or digital signals that characterize the rotational speed and/or the phase relationship of the clutch halves 24, 25 to each other. The signals may be input in a unit 29 for determining the rotational speed, detecting slippage and/or determining slippages. The detected slippage and/or the rotational speed(s) can be utilized as control criterion for operating the motor 15 and/or the brake 17. The load quantity can be determined based on the slippage.
As shown schematically in
With reference to
The hoist 10 described thus far operates as follows:
The hoist 10 can be used for moving loads (lifting or even pulling in an inclined or horizontal direction), with the loads being connected to the pulling means 11. This may take place on the free end of the pulling means 11 or via a loose roller arranged in a snatch block if the free end of the pulling means 11 is fastened at a fixed suspension point, e.g., the transmission housing 30. When the motor 15 rotates, it transmits the driving torque—via the hysteresis clutch 23 and the transmission 16—to the pocket wheel 13 or to another winding wheel in order to lift or otherwise move the load. If the weight of the load is lower than a force limit F0, this action may take place without any substantial slippage of the hysteresis clutch 23. If the weight of the load is greater than the force limit F0, but smaller than the nominal load-bearing capacity FNom, a slippage occurs on the hysteresis clutch 23. The force limit F0 on the hysteresis clutch 23 corresponds to a torque limit M0. When this torque limit M0 is reached, the slippage s is just still zero. When the torque limit M0 is exceeded, said slippage increases. In so doing, the hysteresis clutch 23 preferably shows a linear characteristic 34, i.e., the transmitted torque M increases with increasing slippage s. When the nominal load-bearing capacity FNom is reached, the nominal torque MNom is applied to the hysteresis clutch 23, this resulting in the slippage sNom. The nominal slippage sNom ranges between 0 and 1. For example, it may be 5% or 10% greater. Preferably, it is selected in such a manner that the nominal load can still be lifted smoothly, however at a clearly reduced speed, in order to signal to the operator that the nominal load has been reached.
If higher speeds (e.g., nominal speed) are to be reached with nominal load, the gear reduction may be accomplished, i.e., set in such a manner that, despite slippage, the desired higher speed is reached. The advantage of such a selection of transmission is that partial loads can be moved more rapidly and that the work efficiency is thus increased.
It should be noted that the torque/slippage characteristic must not necessarily be linear. As indicated in
Furthermore, by setting the torque limit M0 lower than the torque limit MNom a smooth operation 10 can be achieved even if the motor 15 is operated without an inverter with mains current at a fixed rotational speed.
With the use of the optional motor-side brake 17a—either as the only brake or in combination with the transmission-side brake—a shock-like stress of the pulling means 11 can also be prevented or minimized during a stopping operation.
If two brakes 17, 17a are being used, they must be activated in such a manner that, first, the motor-side brake 17a is braking and, subsequently—delayed—the transmission-side brake 17 is braking. After the motor-side brake 17a has been actuated, the motor rotational speeds 36 and 38 drop rapidly. The load is decelerated gently by the hysteresis clutch 23 that now acts like a hysteresis brake. The gentle deceleration of the load is shown by dashed lines in
From the foregoing, it can be seen that the hoist 10 in accordance with the invention includes a powertrain 14 that comprises a hysteresis clutch 23. The clutch transmits torques of a driving motor 15 to a transmission 16 and, in so doing, drives a pulling means 11. The hysteresis clutch 23 is adjusted in such a manner that it exhibits a slippage clearly different from zero already before the nominal load-bearing capacity FNom on the pulling means is reached. If the hoist is operated within the range of or near its nominal load-bearing capacity FNom , the device operates at continuous slippage. The resultant waste heat is preferably discharged, via an oil bath, to the wall of the transmission housing which, in so doing, acts as a cooling surface.
The subject hoist 10 allows slimmer dimensioning and displays improved operating properties. Its hysteresis clutch 23 allows the use as a hysteresis brake with controlled emergency load lowering; it acts as a vibration damper for absorbing load vibrations; it can act as a safe torque-limiting unit in the case of an emergency switch-off while the load is being stopped by means of the transmission-side brake 17 and the motor 16 is continued to be operated, and/or it can act for the operator as a load indicator as a result of load-dependent changes of the load lifting rate at constant motor rotational speed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2014 101 654.8 | Feb 2014 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/052651 | 2/9/2015 | WO | 00 |
