JP7677255B2 - Friction drive roller winch - Google Patents

Description

The present invention relates to a winch that can be used to let out and take up a tether that connects a tethered flying object, such as a kite or balloon, to the ground in a kite system, and more specifically, to tension control technology for a friction drive roller (capstan drum) type winch.

In a kite system, a winch capable of continuous operation is useful as a ground facility for taking in and out a long tether that connects a tethered aircraft to the ground under conditions that vary from high tension to low tension depending on the operating altitude and distance. Known winch structures include a system in which a single spool is used to store the tether and generate and control tension, and a friction drive roller system or a capstan drum system (hereinafter referred to as the "FDR system"). The FDR system is a system in which a powered pulley called a capstan drum or friction drive roller is placed between the spool and the load, and the pulley generates tension by pulling. As an example of the former structure, Patent Document 1 discloses a winch in which a rope winding drum (spool) is rotated by an electric motor, and the electric motor is controlled so that the rope tension obtained from a rope tension detection device becomes the target tension. As an FDR type winch, Patent Document 2 proposes a configuration in which a means for constantly applying back tension to the capstan when the wire is wound is mechanically configured to prevent the wire from being wound around the capstan. Patent Document 3 discloses a configuration having a capstan that generates torque in the direction in which the tape in a video tape recorder is fed from the supply reel through the playback head to the take-up reel, and proposes that a mechanism is provided to constantly generate back tension on the tape from the capstan to the supply reel, and that in a mode in which tape feeding is stopped intermittently, a torque is generated on the capstan to offset the back tension even when tape feeding is stopped, stabilizing the tape running.

Japanese Unexamined Patent Publication No. 60-252593 Japanese Patent Application Publication No. 2-255431 JP 10-3713 A

In the winch for the tether connecting the above-mentioned tethered aircraft to the ground, the tension between the load (the tethered aircraft) fluctuates greatly, so an FDR-type winch that generates tension using a friction drive roller is advantageously used. In the case of an FDR-type winch, it is necessary to always apply an appropriate tension to the tether on the spool side (upstream side) of the friction drive roller (hereinafter referred to as "FDR"). This is because if the back tension of the tether on the upstream side of the FDR is not applied, the tether will not be pressed against the circumferential surface of the FDR, and sufficient friction force will not be generated between the tether and the circumferential surface of the FDR, causing the tether to slip on the circumferential surface of the FDR, and the desired tension will not be generated between the load and the FDR. Furthermore, if there is no back tension, and the spool is rotating at high speed due to the tether being pulled out with high load tension, if the load tension suddenly drops, the spool will rotate more than necessary due to inertia, causing excess tether to be sent out from the spool, which can easily cause the tether to float up from the FDR or become tangled.

In the above kite system, the altitude and distance of the tethered aircraft from the ground fluctuate greatly, so the tension of the tether and the length of the tether that is released change greatly, and there are also cases where the tension of the tether connected to the tethered aircraft should be set to zero (for example, when the tethered aircraft is gliding or landing). On the other hand, conventional general FDR type winches are basically configured to steadily pull a load that hardly changes. In that case, when back tension is applied to the tether between the FDR and the spool, tension is always applied to the tether on the load side, so the tension cannot be set to zero. In addition, when the tension on the load side falls below the back tension, it is difficult to change the back tension in accordance with the desired reduction in tension on the load side (as mentioned above, if the back tension is lowered too much, the tether will float up from the FDR or become tangled). Therefore, when using an FDR-type winch in a kite system, it is advantageous to have a configuration that can control the tension of the tether between the load and the FDR to a desired tension of 0 or more, even when back tension is acting on the tether between the FDR and the spool.

Thus, one object of the present invention is to provide a configuration in an FDR-type winch as described above that can control the tension of the tether between the load and the FDR to a desired tension of 0 or more even when back tension is acting on the tether between the FDR and the spool.

According to the present invention, the above problem is solved by a friction drive roller type winch for paying out and taking up a tether connected to a load, comprising:
a spool for winding and storing the tether;
a spool rotational torque imparting device that imparts a rotational torque to the spool;
a friction drive roller around which the tether is wound between the load and the spool;
a drive roller rotation torque imparting device that imparts a rotation torque to the friction drive roller;
a control device for controlling the rotational torque applied by the spool rotational torque application device and the drive roller rotational torque application device so that the tension of the tether between the load and the friction drive roller coincides with a target tension,
This is achieved by a winch configured so that the control device generates a rotational torque in the spool rotational torque imparting device in a direction to wind the tether toward the spool side so that a first tension of a predetermined value or more is generated between the spool and the friction drive roller, and when the magnitude of the target tension on the load side exceeds the magnitude of the first tension, the drive roller rotational torque imparting device generates a rotational torque in a direction to wind the tether toward the spool side, and when the magnitude of the target tension on the load side falls below the magnitude of the first tension, the drive roller rotational torque imparting device generates a rotational torque in a direction to pay out the tether from the spool side.

In the above configuration, the "load" may be any object connected to the tether and moored or held at any position via the winch, for example, but not limited to, a moored aircraft when the winch is used in a kite system. The "spool" is a reel-like member having a cylindrical or columnar shape, around which the tether is wound as described above, and for storing the tether, the length of which is adjusted according to the distance to the load's holding position. The "friction drive roller (FDR)" is a roller also called a capstan drum, around which the tether connected between the load and the spool is wound several times, and is a member that has the function of balancing the frictional force acting between the peripheral surface and the tether and the tension between the load, thereby adjusting the tension between the load and the spool in the tether. The "spool rotation torque imparting device" and the "drive roller rotation torque imparting device" may be any device that imparts rotation torque to the spool and the FDR, respectively, and may typically be a motor. The "target tension" is a target value of the tension for pulling the load, and may be determined appropriately depending on the load. For example, if the load is a tethered aircraft, the target tension may be determined appropriately based on the target and actual values of the altitude, the target and actual values of the ascent and descent speeds, etc. The "control device" may be any device that controls the rotational torque generated in the spool rotational torque imparting device and the drive roller rotational torque imparting device so that the tension of the tether between the load and the FDR matches the target tension, and may be an electronic control device or a computer device. The tension of the tether between the load and the FDR and the tension between the FDR and the spool may each be detected by a tension sensor.

In the above-mentioned configuration of the present invention, first, a rotational torque is generated in the spool by the spool rotational torque imparting device in a direction to wind the tether toward the spool side so that a first tension (i.e., back tension) of a predetermined value or more is generated between the spool and the FDR, thereby generating back tension in the tether between the spool and the FDR. The predetermined value for the first tension is a tension that presses the tether against the peripheral surface of the FDR and generates a frictional force sufficient to suppress slippage in the circumferential direction of the FDR between the tether and the peripheral surface of the FDR, and the first tension may be an appropriately set value equal to or greater than the predetermined value. On the other hand, in the FDR, when the magnitude of the target tension on the load side exceeds the magnitude of the first tension, i.e., the magnitude of the back tension, a rotational torque is generated by the drive roller rotational torque imparting device in a direction to wind the tether, and when the magnitude of the target tension on the load side falls below the magnitude of the first tension, a rotational torque is generated in the drive roller rotational torque imparting device in a direction to send out the tether. That is, in the present invention, the magnitude and direction of the torque generated in the FDR are determined so that the difference between the tensions of the tether before and after the FDR is equal to the target tension minus the back tension, while a back tension of a predetermined value or more is always generated in the tether between the spool and the FDR. In this configuration, the rotational torque of the FDR is generated and adjusted not only in the winding direction of the tether but also in the releasing direction of the tether, while the back tension that winds the tether around the circumferential surface of the FDR is always acting on the tether between the spool and the FDR. Therefore, when the tension required for the tether connected to the load falls below the back tension, the rotational torque of the FDR in the releasing direction of the tether can offset the back tension, and the tension of the tether connected to the load can be appropriately adjusted not only in the range above the back tension, but also in the range below the back tension.

According to the above-mentioned configuration of the present invention, when the target tension of the tether connected to the load is 0, a rotational torque is applied to the FDR in the direction of feeding out the tether so that the tension of the tether between the load and the FDR is set to 0 with a first tension being generated in the tether between the spool and the FDR. In other words, even if the tension of the tether connected to the load is 0, tension acts on the tether at the spool and the FDR, and a force is generated that presses the tether against each of the peripheral surfaces, so that the tether is prevented from floating up at the spool and the FDR, and tangles in the tether can be avoided.

In an embodiment, the rotational torque T _spool generated on the spool may be given by the following formula using the back tension (target value) F _backside , the winding radius r _spool of the tether on the spool, the moment of inertia I _spool , and the angular acceleration d ² θ _spool /dt ² (assuming that the winding direction of the tether is >0 and there is no slippage of the tether on the spool; the same applies below).
T _spool = r _spool・F _backside +I _spool・d ² θ _spool /dt ² … (1a)
That is, the rotational torque _Tspool generated in the spool may be a value obtained by adding an inertia term to the torque generating the back tension. However, since the inertia term is 0 while the rotational speed is constant, the target value of the rotational torque _Tspool may be given by _rspool · _Fbackside . On the other hand, the rotational torque _Tdrive generated in the FDR may be given by the following formula using the back tension (target value) _Fbackside , the tension _Ffrontside on the load side, the winding radius _rdrive of the tether of the FDR, the _moment of inertia _Idrive , and the angular acceleration ^d2θdrive / ^dt2 .
T _drive = r _drive・(F _frontside −F _backside ) +I _drive・d ² θ _drive /dt ² …(1b)
That is, the rotational torque _Tdrive generated in the FDR may be a value obtained by adding an inertia term to the rotational torque that generates tension obtained by subtracting the back tension from the tension on the load side. However, since the inertia term is 0 while the rotational speed is constant, the target value of the rotational torque _Tdrive may be _rdrive ·( _Ffrontside - _Fbackside ). As can be understood from the formula (1b), when _Ffrontside < _Fbackside (when the rotational speed is constant), _Tdrive < 0, that is, the rotational torque is applied in the direction of letting out the tether.

In the above configuration of the present invention, the back tension may be set so that the tether is pressed against the spool and the FDR with an appropriate pressing force, and in one embodiment, the back tension may be maintained constant regardless of the tension of the tether between the load and the FDR. In another embodiment, when a rotational torque is generated in the direction in which the tether is fed out to the drive roller rotational torque imparting device, the rotational torque generated in the direction in which the tether is wound on the spool rotational torque imparting device may be reduced so that the tension of the tether between the spool and the FDR does not fall below a predetermined value. When a rotational torque is generated in the direction in which the tether is fed out to the drive roller rotational torque imparting device, that is, when the magnitude of the tension of the tether between the load and the FDR is smaller than the magnitude of the back tension, the tension in the load direction is low, so that the tether is likely to be wound on the spool side. In this case, the back tension may be reduced as described above to suppress excessive winding of the tether on the spool side.

Thus, according to the above-mentioned configuration of the present invention, in an FDR-type winch, when back tension is applied to the tether between the spool and the FDR, the tension of the tether between the load and the FDR can be controlled to be lower than the back tension. As already mentioned, in a kite system, the altitude, distance, and moving speed of the tether-connected flying object fluctuate greatly, and the magnitude of the tension to be generated in the tether fluctuates within a range of 0 or more. In such a system, the above-mentioned winch according to the present invention can appropriately adjust the tension to be generated in the tether while keeping the tether between the spool and the FDR under back tension, so that it is expected that the occurrence of winch troubles such as tether tangling can be suppressed. The configuration of the winch of the present invention may be used for any purpose, not limited to kite systems.

Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the present invention.

Fig. 1(A) is a schematic diagram of a kite system to which the winch according to the present embodiment is applied, and Fig. 1(B) is a block diagram showing the configuration of a control device for controlling the rotational torque of a spool and an FDR in the winch according to the present embodiment. FIG. 2 is a diagram for explaining the relationship between the tether tension and rotational torque in the winch spool and FDR according to this embodiment. 3A and 3B are graphs showing the tension F generated in the spool and the FDR with respect to the tension (target value) F _frontside in the tether between the load and the winch according to the present embodiment. (A) is a first embodiment, and (B) is a second embodiment. FIG. 4 is a diagram for explaining the relationship between the spool of a winch having a plurality of FDRs according to this embodiment and the tension of the tether and the rotational torque in the FDRs.

1... Kite system 2... Tethered aircraft (kite)
3... Tether 4... Winch 5... Spool 5m... Spool rotation motor (spool rotation torque imparting device)
6...Friction drive roller (FDR)
6 m... Friction drive roller (FDR) rotation motor (drive roller rotation torque imparting device)
7... Pulley 10... Tension sensor of tether between spool and FDR 11... Tension sensor of tether between FDR and load 20... Rotational torque control device

Basic configuration of the winch The winch of this embodiment may be used as a winch 4 connected to an aircraft 2 such as a kite or balloon in a kite system 1 as shown in FIG. 1A, for example, to pull out and reel in a tether 3 for mooring the aircraft 2 in the air. In short, the winch 4 is an FDR type winch having a spool 5 for winding and storing the tether 3, and a friction drive roller 6 (hereinafter referred to as "FDR") around which the tether 3 is wound and rotated between the spool 5 and the tethered aircraft 2. In short, in a system using the winch 4, one end of the tether 3 wound around the periphery of the spool 5 is pulled out from the spool 5, wound around the periphery of the FDR 6 several times, and then connected to the tethered aircraft 2 (the tether may be wound around a pulley 7 provided at an appropriate position). In this configuration, since a frictional force acts between the tether 3 and the circumferential surface of the FDR 6, when the tethered aircraft 2 is lifted into the air by wind, the tension acting on the tether 3 on the side of the tethered aircraft 2 from the FDR 6 is not transmitted as is to the spool 5, and the tension acting on the tether 3 between the FDR 6 and the spool 5 is the tension minus the tension generated by the rotational torque acting due to the frictional force between the tether 3 and the circumferential surface of the FDR 6. As a result, when the tether 3 is pulled out and wound on the spool 5 to adjust the length of the tether 3 according to the distance from the spool 5 to the tethered aircraft 2, the winding force of the tether 3 around the circumferential surface of the spool 5 is stabilized, and damage or entanglement of the tether 3 can be prevented.

Configuration of the Rotational Torque Control Device In the above-mentioned winch configuration, the spool 5 and the FDR 6 are connected to rotational motors 5m and 6m, respectively, and rotational torque is applied from these motors. The tension of the tether 3 connected to the load is adjusted by controlling the rotational torque applied to the spool 5 and the FDR 6. Referring to FIG. 1B, the rotational torque in the spool 5 and the FDR 6 is controlled by a rotational torque control device 20. The control device 20 may be an electronic control device or a computer device. In the control device 20, first, a target value (target tension) Ff_t of the tension for pulling the tether 3 connected to the load is determined by a target tension determination unit 20a based on the state (difference between the required altitude and the actual altitude, the moving speed, etc.) of the load (tethered aircraft 2). Then, by referring to the target tension Ff_t, the control command determination unit 20b determines the magnitude and direction of the rotational torque to be generated by the rotational motors 5m, 6m, as described below, and control commands _Cspool , _Cdrive for the rotational torque are given to the rotational motors 5m, 6m, and the rotational torque is applied to the spool 5 and the FDR 6 by the rotational motors 5m, 6m. The rotational torque control may be feedforward control based on the target tension Ff_t, but may also be performed by feedback control by referring to the actual value of the tension in the tether 3. In that case, a tension sensor 10 for detecting the tension of the tether 3 between the spool 5 and the FDR 6 and a tension sensor 11 for detecting the tension of the tether 3 between the FDR 6 and the load 2 may be provided, and the rotational torque may be controlled using the detection values of these tension sensors.

As mentioned in the Summary of the Invention section, in the configuration of the winch 4 described above, it is preferable to always apply back tension between the spool 5 and the FDR 6 in the winding direction of the tether 3 in order to press the tether 3 against the circumferential surface of the FDR 6 to generate a frictional force between the tether 3 and the circumferential surface of the FDR 6 for transmitting the rotational torque of the FDR 6 to the tether 3, and to prevent over-rotation of the spool 5 in the payout direction of the tether. Therefore, in controlling the above rotational torque, the control command determination unit 20b is further configured to determine the rotational torque to be generated by the rotation motors 5m and 6m by referring to the back tension Fb_t to be generated in the tether 3 between the spool 5 and the FDR 6.

Improvement of rotational torque control in FDR 6 (a) Overview As described above, when back tension is constantly applied to the tether 3 between the spool 5 and the FDR 6, the back tension is always added to the tension of the tether between the FDR 6 and the load 2. In this regard, in the case of a conventional winch, for example, a winch for pulling lumber at a forestry site, the tension required for pulling a load does not fluctuate significantly, and a situation does not occur in which the tension falls below the back tension while pulling the load. In contrast, when pulling a tethered aircraft 2 of a kite system, the tethered aircraft 2 takes various states in the air, such as stationary, ascending, descending, forward, backward, gliding, etc., so the tension (target tension) required for the tether 3 connected to the tethered aircraft 2 and pulling it fluctuates significantly. And, in particular, in the tether 3 connected to the tethered aircraft 2 of a kite system, a situation occurs in which a target tension below the back tension is required. Therefore, as already mentioned, in the winch for the tether that moors the tethered aircraft 2 of the kite system, it is preferable that the target tension can be set arbitrarily within a range of 0 or more while always generating back tension in the tether 3 between the spool 5 and the FDR 6. Therefore, in this embodiment, a rotational torque is always applied to the spool 5 in the winding direction of the tether, and while back tension is applied to the tether 3 between the spool 5 and the FDR 6, the rotational torque applied to the FDR 6 is applied not only in the winding direction of the tether but also in the releasing direction of the tether, so that the tension of the tether between the FDR 6 and the load 2 can be arbitrarily set within a range of 0 or more.

(b) Rotational Torque Control in Spool and FDR In this embodiment, the rotational torque applied to the spool 5 and FDR 6 may be controlled as follows.

Referring to FIG. 2, first, in the spool 5, the relationship between the tension (back tension) F _backside generated in the tether 3 and the rotational torque T _spool is given by the following equation of motion (the winding direction of the tether is positive; the same applies below).
I _spool・d ² θ _spool /dt ² =T _spool −r _spool・F _backside …(2a)
Here, I _spool is the moment of inertia of the spool, d ² θ _spool /dt ² is the angular acceleration of the spool, and r _spool is the radius of the surface around which the tether is wound around the spool. The back tension F _backside is a target value of tension that is appropriately set so that the tether 3 does not substantially slip in the circumferential direction on the circumferential surface of the FDR 6, and can be determined in advance by experiment or the like. Therefore, the rotational torque applied to the spool 5 is
T _spool = r _spool・F _backside +I _spool・d ² θ _spool /dt ² … (1a)
In addition, the angular acceleration d ² θ _spool /dt ² is 0 when the angular velocity is considered to be constant, so the target value of the rotational torque T _spool applied to the spool 5 is expressed as follows:
T _spool = r _spool・F _backside …(3a)
may be given by

On the other hand, in the FDR 6, the relationship between the tension F _frontside and back tension F _backside generated in the load side tether 3, and the rotational torque T _drive is given by the following equation of motion.
I _drive・d ² θ _drive /dt ² =T _drive −r _drive・(F _frontside −F _backside )…(2b)
Here, I _drive is the moment of inertia of the FDR, d ² θ _drive /dt ² is the angular acceleration of the FDR, and r _drive is the radius of the winding surface of the tether of the FDR. The tension F _frontside generated in the load side tether 3 is the target tension Ff_t, and as already mentioned, is set appropriately based on the load condition such as the difference between the required altitude and the actual altitude of the tethered aircraft 2, the moving speed, etc. Therefore, the rotational torque applied to the FDR 6 is
T _drive = r _drive・(F _frontside −F _backside ) +I _drive・d ² θ _drive /dt ² …(1b)
In addition, _the angular acceleration ^d2θdrive / ^dt2 is 0 when the angular velocity is considered to be constant, so the target value of the rotational torque _Tdrive applied to the FDR 6 is
T _drive = r _drive・(F _frontside −F _backside ) …(3b)
As can be seen from the formula (3b), when the tension F _frontside generated in the tether 3 on the load side exceeds the back tension F _backside , the rotational torque T _drive is >0 and is applied in the winding direction of the tether, whereas when the tension F _frontside generated in the tether 3 on the load side is below the back tension F _backside , the rotational torque T _drive is <0 and is applied in the releasing direction of the tether.

3A, when a rotational torque is applied to the spool and FDR as described above, the tension of the tether between the spool and FDR is _Tspool / _rspool as shown by the dotted line in the figure, and the target tension _Ffrontside for pulling the load is further added with the tension _Tdrive / _rdrive (thick solid line in the figure) given by the FDR, and becomes _Tspool / _rspool + _Tdrive / _rdrive (thin solid line in the figure). As shown in the figure, the tension _Tdrive / _rdrive given by the FDR becomes 0 at the tension Fc where the target tension _Ffrontside = _Fbackside , and becomes < 0 in the range where _Ffrontside < _Fbackside , and when _Ffrontside = 0, _Tdrive / _rdrive = _-Fbackside . That is, when the target tension is 0, a rotational torque may be applied to the FDR such that the tension generated by the rotational torque of the FDR cancels out the tension generated by the rotational torque of the spool.

In the above configuration, as shown in Fig. 3A, the back tension F _backside may be constant regardless of the target tension F _frontside generated in the load side tether 3. In this regard, in a range where the target tension F _frontside is lower than the back tension F _backside , the target tension F _frontside becomes relatively small, and the tether is easily wound onto the spool. Therefore, in order to prevent the tether from being excessively wound onto the spool, as shown in Fig. 3B, the back tension F _backside may be reduced together with the reduction in the target tension F _frontside in a range where F _frontside < F _backside . The minimum value Fo of the back tension F _backside may be set through experiments or the like so that the tension is such that a sufficient pressing force is applied to the tether to prevent the tether from slipping on the FDR circumferential surface.

(c) Configuration using multiple FDRs In the winch of this embodiment, multiple FDRs (6_1, 6_2) may be provided. In this case, as shown in Fig. 4, the tension on the downstream side (load side) of the tether in each FDR 6_1, 6_2 is the tension on the upstream side (spool side) plus T _drive(i) /r _drive(i) (i is the FDR number). The total tension added by the FDR is F _frontside - F _backside , and the distribution of the rotational torque applied to each FDR may be determined by any method.

(d) Estimation of the Winding Radius of the Tether on the Spool In the above-described control of the rotational torque, the radius r _drive of the winding surface of the tether on the FDR hardly changes, but the radius r _spool of the winding surface of the tether on the spool (and the moment of inertia I _spool ) changes depending on the amount of wound tether. In this regard, in order to control the rotational torque more accurately, a value detected by a sensor or the like may be used for r _spool , or it may be estimated from the motion history of the spool.

Specifically, the moment of inertia I of the spool with the tether wound thereon is calculated by using the radius ro of the spool without the tether wound thereon, the moment of inertia Io, the width d of the spool, and the density ρ of the _tether .
I _spool = Io + 1/2・ρ・d・(r _spool ⁴ −ro ⁴ ) …(4)
In addition, I _spool is given by the following equation (2a): I _spool = (T _spool - _{r spool} · F _backside ) / (d ² θ _spool / dt ² ) (5)
Here, since parameters other than r _spool are known values or measured values, it is possible to numerically calculate r _spool (>ro) that satisfies the equation obtained by eliminating the moment of inertia I _spool from equations (4) and (5).

Thus, in this embodiment, when the target value of the tension of the tether towing the load falls below the back tension of the tether between the spool and the FDR, tension in the direction of sending out the tether is applied to the FDR, making it possible to adjust the tension of the tether towing the load within a range of 0 or more while always applying back tension to the tether between the spool and the FDR. With this configuration, even if the tension of the tether between the load fluctuates significantly, the tether is kept stably wound around the FDR, and problems such as tether tangling can be suppressed. The winch of this embodiment described above may be used in any FDR-type winch for any purpose, not just in kite systems.

The above description is given in relation to an embodiment of the present invention, but many modifications and variations are easily possible for those skilled in the art, and it will be apparent that the present invention is not limited to the embodiment exemplified above, but can be applied to various devices without departing from the concept of the present invention.

Claims (3)

1. A friction drive roller type winch for letting out and reeling in a tether connected to a load, comprising:
a spool for winding and storing the tether;
a spool rotational torque imparting device that imparts a rotational torque to the spool;
a friction drive roller around which the tether is wound between the load and the spool;
a drive roller rotation torque imparting device that imparts a rotation torque to the friction drive roller;
a control device for controlling the rotational torque applied by the spool rotational torque application device and the drive roller rotational torque application device so that the tension of the tether between the load and the friction drive roller coincides with a target tension,
The control device causes the spool rotational torque imparting device to generate a rotational torque in a direction to wind the tether toward the spool side so that a first tension of a predetermined value or more is generated between the spool and the friction drive roller, and when the magnitude of the target tension toward the load side exceeds the magnitude of the first tension, the drive roller rotational torque imparting device generates a rotational torque in a direction to wind the tether toward the spool side, and when the magnitude of the target tension toward the load side falls below the magnitude of the first tension, the drive roller rotational torque imparting device generates a rotational torque in a direction to pay out the tether from the spool side. The winch of claim 1, in which, when the target tension is 0, a rotational torque is applied to the friction drive roller in a direction that pays out the tether so that the tension of the tether between the load and the friction drive roller is set to 0 in a state in which the first tension is generated in the tether between the spool and the friction drive roller. A winch according to claim 1 or 2, which reduces the rotational torque generated in the spool rotational torque applying device in the direction of winding the tether when the drive roller rotational torque applying device applies a rotational torque in the direction of letting out the tether, so that the tension of the tether between the spool and the friction drive roller does not fall below the predetermined value.

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