SPORTING APPARATUS AND CONTROL METHOD THEREOF

Abstract

A sporting apparatus comprises a structure body, an endless belt, an electricity generating unit and a position sensing unit. The endless belt is disposed on the structure body. The electricity generating unit is disposed in the structure body and transforms kinetic energy, which is transmitted from the endless belt, into electric power. The position sensing unit is disposed in the structure body and senses a position of a user on the endless belt so as to generate a sensing signal. An armature current of the electricity generating unit is adjusted according to the sensing signal for controlling a rotation speed of the endless belt. A control method of the sporting apparatus is also disclosed.

Description

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a sporting apparatus and, in particular, to a sporting apparatus which is rotation speed controllable.

2. Related Art

More and more people are busy in their works and social activities, so they do not have time to do exercise. Consequently, many kinds of sporting apparatuses are invented for these busy people. For example, a running machine 1 as shown in FIG. 1 allows the user to do running exercise anytime and anywhere.

The running machine 1 includes a motor 11 and an endless belt 12. The motor 11 can drive the endless belt 12 to rotate, so that the user can run on the rotating endless belt 12. This allows the user to work out at home or gym.

However, the running machine 1 must be powered on to enable the motor 11 to drive the endless belt 12 to rotate, and the running machine 1 is high power consumption. In addition, when the rotation speed of the endless belt 12 is set already, the user can only passively run following the set rotation speed of the endless belt 12. Since the running machine 1 can not adjust the rotation speed of the endless belt 12 according to the position of the user on the endless belt 12, the user may fall down and get hurt if the running speed of the user does not compete with the rotation speed of the endless belt 12.

Therefore, it is a subject of the invention to provide a sporting apparatus and a control method thereof that do not need the external power for driving and can adjust the rotation speed of the endless belt according to the position of the user on the endless belt so as to prevent the user from getting hurt.

SUMMARY OF THE INVENTION

In view of the foregoing, an objective of the invention discloses a sporting apparatus and a control method thereof that do not need the external power for system driving and can adjust the rotation speed of the endless belt according to the position of the user on the endless belt so as to prevent the user from getting hurt.

To achieve the above objective, the present invention discloses a sporting apparatus comprising a structure body, an endless belt, an electricity generating unit and a position sensing unit. The endless belt is disposed on the structure body. The electricity generating unit is disposed in the structure body and transforms kinetic energy, which is transmitted from the endless belt, into electric power. The position sensing unit is disposed in the structure body and senses a position of a user on the endless belt to generate a sensing signal. Then, an armature current of the electricity generating unit is adjusted according to the sensing signal for controlling a rotation speed of the endless belt.

In one embodiment of the invention, the sporting apparatus further comprises a transmission mechanism disposed in the structure body and connected with the endless belt and the electricity generating unit.

In one embodiment of the invention, the sporting apparatus further comprises a modulation unit electrically connected with the electricity generating unit and the position sensing unit. The modulation unit controls the armature current according to the sensing signal so as to change the rotation speed of the endless belt, so that the user is kept on a specific position of the endless belt. Besides, the modulation unit may control the armature current by pulse width modulation or by modulating an output power of the electricity generating unit.

In one embodiment of the invention, the sporting apparatus further comprises at least a piezo-electric element disposed in the endless belt.

In one embodiment of the invention, the sporting apparatus further comprises a start auxiliary unit, which is electrically connected with the electricity generating unit and provides a start voltage.

To achieve the above objective, the present invention also discloses a control method applied to a sporting apparatus. The sporting apparatus includes an endless belt, and the endless belt rotates to drive an electricity generating unit to generate an armature current. The method includes the following steps of: sensing a position of a user on the endless belt so as to generate a sensing signal, adjusting the armature current according to the sensing signal, and controlling a rotation speed of the endless belt according to the armature current.

In one embodiment of the invention, the step of sensing the position of the user on the endless belt so as to generate the sensing signal is performed by a position sensing unit. The step of adjusting the armature current according to the sensing signal is performed by a modulation unit. The modulation unit controls the armature current by pulse width modulation; otherwise, the modulation unit controls the armature current by modulating an output power of the electricity generating unit. Moreover, the modulation unit alters the armature current so as to change the rotation speed of the endless belt, so that the user is kept on a specific position of the endless belt. The rotation speed of the endless belt increases when the armature current decreases; on the contrary, the rotation speed of the endless belt decreases when the armature current increases.

As mentioned above, the sporting apparatus of the invention is configured with an electricity generating unit for transforming kinetic energy transmitted from the endless belt into electric power and a position sensing unit for sensing a position of a user on the endless belt so as to generate a sensing signal. Furthermore, the armature current of the electricity generating unit is adjusted according to the sensing signal for controlling a rotation speed of the endless belt. Therefore, the sporting apparatus does not need the external power and can adjust the rotation speed of the endless belt according to the position of the user on the endless belt. Accordingly, the user can be kept on the specific position of the endless belt so as to protect the user from falling down and getting hurt due to that the running speed of the user does not compete with the rotation speed of the endless belt. As a result, in the sporting apparatus and control method thereof of the invention, the external power is not necessary and the user can be protected from falling down and getting hurt.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the subsequent detailed description and accompanying drawings, which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is a schematic diagram showing a part of the conventional running machine;

FIG. 2 is a schematic diagram showing a sporting apparatus according to an embodiment of the invention;

FIG. 3 is a block diagram of the sporting apparatus according to the embodiment of the invention;

FIGS. 4A to 4F are block diagrams of several aspects of parts of the sporting apparatus according to the embodiment of the invention;

FIG. 5 is a block diagram of another aspect of parts of the sporting apparatus according to the embodiment of the invention; and

FIG. 6 is a flow chart of a control method of the sporting apparatus according to the embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.

A sporting apparatus 2 according to an embodiment of the invention will be described hereinafter with reference to FIGS. 2 and 3, wherein FIG. 2 is a schematic diagram showing the sporting apparatus 2, and FIG. 3 is a block diagram of the sporting apparatus 2.

The sporting apparatus 2 comprises a structure body 21, an endless belt 22, an electricity generating unit 23, and a position sensing unit 24. Moreover, the sporting apparatus 2 further comprises a transmission mechanism 25 and a modulation unit 26. To be noted, the sporting apparatus 2 of the invention is not the conventional running machine, so that the external power is not necessary for the sporting apparatus 2. In the embodiment, the kinetic energy generated by a user can rotate the endless belt 22 so as to enable the electricity generating unit 23 of the sporting apparatus 2 to generate electricity. In addition, the electricity generated by the electricity generating unit 23 can be applied to drive elements of the sporting apparatus 2 or to charge an energy storage device. Besides, it can also be applied to a load or be sold to the power company. However, the applications of the generated electricity are not limited to this embodiment.

The endless belt 22 is disposed on the structure body 21 through two rotation shafts, so that it can rotate relative to the structure body 21. In other words, the endless belt 22 is disposed on the structure body 21, and the structure body 21 stands still while the endless belt 22 rotates. In this case, the endless belt 22 is a rubber belt for example. Of course, it can also be a track.

The electricity generating unit 23 is disposed in the structure body 21, and it is used to transform kinetic energy, which is transmitted from the endless belt 22, into electric power. The electricity generating unit 23 can be, for example but not limited to, a permanent-magnet generator, an induction generator, or a DC generator (including brush and commutator).

The transmission mechanism 25 is disposed in the structure body 21 and connected with the endless belt 22 and the electricity generating unit 23. Thus, the transmission mechanism 25 can transmit kinetic energy of the rotating endless belt 22 to the electricity generating unit 23. In other words, when the user runs on the endless belt 22, the endless belt 22 is rotated and the transmission mechanism 25 can transform kinetic energy of the rotating endless belt 22 into torque and then transmit the torque to the electricity generating unit 23. Thus, the electricity generating unit 23 can generate electricity. In addition, since the electricity generating unit 23 is a generator, an armature current Ia of the electricity generating unit 23 is in positive proportion with the counter torque of the electricity generating unit 23. When the armature current Ia of the electricity generating unit 23 is altered, the counter torque of the electricity generating unit 23 is relatively changed in proportion. Accordingly, the transmission mechanism 25 can also change the rotation speed of the endless belt 22 depending on the counter torque variation of the electricity generating unit 23. In other words, when the counter torque of the electricity generating unit 23 is altered, the transmission mechanism 25 can change the rotation speed of the endless belt 22 according to the counter torque variation of the electricity generating unit 23. In this embodiment, the transmission mechanism 25 is, for example but not limited to, a set of planetary gears, a gear box, or a set of belts.

The position sensing unit 24 is disposed in the structure body 21 and senses a position of the user on the endless belt 22 so as to generate a sensing signal SS. For example, the position sensing unit 24 may comprise an ultrasonic sensor, an infrared sensor, or a piezo-electric sensor. In this embodiment, the position sensing unit 24 is an ultrasonic sensor. In addition, the armature current Ia of the electricity generating unit 23 is adjusted according to the sensing signal SS. Once the armature current Ia changes, the counter torque of the electricity generating unit 23 is relatively changed so as to control the rotation speed of the endless belt 22.

The modulation unit 26 is electrically connected with the electricity generating unit 23 and the position sensing unit 24, and the modulation unit 26 controls the armature current Ia according to the sensing signal SS. When the modulation unit 26 alters the armature current Ia, the counter torque of the electricity generating unit 23 and the rotation speed of the endless belt 22 are relatively changed. Thus, the user is kept on a specific position of the endless belt 22. In this embodiment, the specific position of the endless belt 22 represents the center region B of the endless belt 22 in FIG. 2.

In other words, if the running speed of the user does not compete with the rotation speed of the endless belt 22 (e.g. when the running speed of the user is faster, or the rotation speed of the endless belt 22 is slower), the user may step forward and be located in front of the region B of the endless belt 22 as shown in FIG. 2. In this case, the position sensing unit 24 detects that the user is located in front of the region B of the endless belt 22, so that it outputs the sensing signal SS to the modulation unit 26. Then, the modulation unit 26 modulates the armature current Ia of the electricity generating unit 23 according to the sensing signal SS. Herein, the modulation unit 26 controls to decrease the armature current Ia. Moreover, since the armature current Ia is in positive proportion with the counter torque, the counter torque of the electricity generating unit 23 is relatively decreased. The decrease of the counter torque of the electricity generating unit 23 achieves the effect of reducing the load of the running endless belt 22, which means that the user can feel an easier level while running on the endless belt 22. Consequently, the rotation speed of the endless belt 22 is increased, so that the user is shifted back to the region B of the endless belt 22.

Alternatively, when the running speed of the user is slower, or the rotation speed of the endless belt 22 is faster, the user may step backward and be located in back of the region B of the endless belt 22 as shown in FIG. 2. In this case, the position sensing unit 24 detects that the user is located in back of the region B of the endless belt 22, so that it outputs the sensing signal SS to the modulation unit 26. Then, the modulation unit 26 modulates the armature current Ia of the electricity generating unit 23 according to the sensing signal SS. Herein, the modulation unit 26 controls to increase the armature current Ia, so that the counter torque of the electricity generating unit 23 is relatively increased too. The increase of the counter torque of the electricity generating unit 23 achieves the effect of increasing the load of the endless belt 22 that means the user can feel a tougher level while running on the endless belt 22. Consequently, the rotation speed of the endless belt 22 is decreased, so that the user is shifted forward to the center region B of the endless belt 22. As a result, when the running speed of the user is not compete with the rotation speed of the endless belt 22, it is possible to dynamically adjust to shift the user to the region B of the endless belt 22.

The procedures of using the modulation unit 26 to adjust the armature current Ia of the electricity generating unit 23 will be described hereinafter with reference to FIGS. 4A to 4D. FIGS. 4A to 4D are block diagrams of several aspects of parts of the sporting apparatus 2 for using the modulation unit 26 to adjust the armature current Ia. To make the descriptions more clear, the blocks of the structure body 21, the endless belt 22, and the transmission mechanism 25 are omitted in FIGS. 4A to 4D. In this embodiment, the electricity generated by the electricity generating unit 23 is applied to a variable load L for example.

As shown in FIG. 4A, when receiving the sensing signal SS generated from the position sensing unit 24, the modulation unit 26a can modulate the equivalent resistance of the variable load L (e.g. the value of the load) to control the armature current Ia.

For instance, if the running speed of the user is faster, the user may step forward and is located in front of the region B of the endless belt 22 (see FIG. 2). In this case, the position sensing unit 24 detects that the user is located in front of the region B of the endless belt 22, so that it outputs the sensing signal SS to the modulation unit 26a for decreasing the armature current Ia of the modulation unit 26a. In practice, the modulation unit 26a outputs a control signal CS to the load L for decreasing the power inputted to the load L. Accordingly, the armature current Ia of the electricity generating unit 23 is decreased. Consequently, the counter torque of the electricity generating unit 23 is decreased too, so that the rotation speed of the endless belt 22 increases. This can automatically shift the user back to the region B of the endless belt 22 (see FIG. 2).

Referring to FIG. 4B, the modulation unit 26b comprises at least one voltage modulation element 261 and a capacitor C. When receiving the sensing signal SS generated from the sensing unit 24, the modulation unit 26b can control the armature current Ia by the voltage modulation element 261.

For instance, if the user steps forward and is located in front of the region A of the endless belt 22 (see FIG. 2), the position sensing unit 24 outputs the sensing signal SS to the modulation unit 26b for decreasing the armature current Ia. In this case, the voltage modulation element 261 controls to increase the voltage differential between two ends of the capacitor C. Accordingly, the voltage differential between the terminal voltage of the capacitor C and the output voltage of the electricity generating unit 23 decreases, so that the armature current Ia decreases. Consequently, the counter torque of the electricity generating unit 23 is decreased too, so that the rotation speed of the endless belt 22 increases. This can automatically shift the user back to the region B of the endless belt 22 (see FIG. 2).

Referring to FIG. 4C, the modulation unit 26c at least comprises a voltage modulation element 261, a current sensor 262, a switch Q, and an inductance L1. When receiving the sensing signal SS generated from the position sensing unit 24, the modulation unit 26c can use the current sensor 262 and the switch Q to control the armature current Ia. In this embodiment, the inductance L1 can be an additional configured component or substituted by the coils of the electricity generating unit 23. In addition, if the modulation unit 26c is coupled to a pure resistor, the voltage modulation element 261 can be omitted.

The current sensor 262 can sense the current flowing through the inductance L1, which is the armature current Ia, and output a signal to the controller (not shown in FIG. 4C) of the modulation unit 26c, so that the controller can control the switch Q. The switch Q is controlled by pulse width modulation so as to control the armature current Ia. In other words, the duty cycle of the switch Q is controlled by pulse width modulation, so that the armature current Ia is controlled.

For instance, if the user steps backward and is located in back of the region B of the endless belt 22 (see FIG. 2), the position sensing unit 24 outputs the sensing signal SS to the modulation unit 26c for increasing the armature current Ia. In this case, the current sensor 262 determines that the current flowing through the inductance L1 is low, so the current sensor 262 outputs a signal to the controller of the modulation unit 26c. Accordingly, the controller of the modulation unit 26c can control the duty cycle of the switch Q for increasing the turn-on period of the switch Q. Accordingly, the current flowing through inductance L1 (the armature current Ia) can be increased. Consequently, the counter torque of the electricity generating unit 23 is increased too, so that the rotation speed of the endless belt 22 decreases. This can automatically shift the user forward to the region B of the endless belt 22 (see FIG. 2).

Referring to FIG. 4D, the current sensor 262 of the modulation unit 26d is disposed at another location different from that shown in FIG. 4C. In this case, the current sensor 262 senses the current flowing through the switch Q and then outputs a signal to the controller (not shown in FIG. 4D) of the modulation unit 26d, so that the controller can control the switch Q. In other words, the current sensor 262 detects the current value of the switch Q during the turn-on period of the switch Q. This detected current value also represents the current flowing through the inductance L1. Similarly, this aspect can also control the armature current Ia as described in the previous aspect of FIG. 4C.

Moreover, if the electricity generating unit 23 is a three-phase generator, the outputted armature current Ia is a three-phase current. Referring to FIG. 4E, the modulation unit 26e may further include a three-phase full-bridge rectifying unit 263, which is composed of six diodes. In addition, the output of the electricity generating unit 23 is rectified by the three-phase full-bridge rectifying unit 263 in advance.

The three-phase full-bridge rectifying unit 263 and the switch Q can be integrated for both rectifying and controlling the armature current Ia. Referring to FIG. 4F, the functions of the three-phase full-bridge rectifying unit 263, the diode D and the switch Q of FIG. 4E are integrated as a rectify-control unit 264 of FIG. 4F. In this case, switches Q1 to Q6 are separately controlled by different pulse width modulations, so that the rectifying and modulating of the armature current Ia can be both achieved. In addition, as shown in FIG. 4F, the coil of the electricity generating unit 23 is used to substitute the inductance L1. Otherwise, it is possible to partially integrate the switches Q with the diodes as shown in FIG. 4E. For example, the upper three diodes of the three-phase full-bridge rectifying unit 263 may perform the rectifying function, while the lower three diodes thereof are integrated with the switches Q for both rectifying and modulating of the armature current Ia (not shown). In addition, the currents Iu, Iv and Iw outputted from the electricity generating unit 23 are in three-phase balance, so the sum of the currents Iu, Iv and Iw is equal to zero (Iu+Iv+Iw=0). Thus, only two current sensors 262 are needed and configured at any two phases outputted from the electricity generating unit 23 for measuring two of the currents, and the current of the residual one phase can be obtained by calculation. For example, as shown in FIG. 4F, after two current sensors 262 sense the currents Iu and Iv outputted from the electricity generating unit 23, the current Iw of the residual phase can be obtained by calculation.

In addition, the sporting apparatus 2 may further comprise at least one piezo-electric element (not shown), which is disposed on the endless belt 22. The configuration of the piezo-electric element can transform the instant impact as the user steps on the endless belt 22 into voltage. The piezo-electric element can utilize the piezo-electric effect to transform mechanical energy into electricity. In other words, the piezo-electric element can generate extra electricity due to the piezo-electric effect, so that the total generated electricity of the sporting apparatus 2 can be increased.

FIG. 5 is a block diagram of another aspect of parts of the sporting apparatus 2 according to the embodiment of the invention. To make the descriptions more clear, the blocks of the structure body 21, the endless belt 22, and the transmission mechanism 25 are also omitted in FIG. 5.

The sporting apparatus 2 may further include a start auxiliary unit 27, which is electrically connected with the modulation unit 26. The start auxiliary unit 27 provides a start voltage V_start before the sporting apparatus 2 is started, so that the armature current Ia can be inhibited while the sporting apparatus 2 is just started and/or is in a low speed. This configuration can decrease the counter torque of the electricity generating unit 23, so that the user can easily drive the endless belt 22 to start rotating. The start voltage V_start can be provided from the city power, battery, or other energy storage device. In addition, it is possible to enable the start auxiliary function by using a sensor to detect the user and/or by pressing a button before the running exercise.

Before the user starts to run on the sporting apparatus 2, the electricity generating unit 23 is controlled to stop providing electricity to the load, and a capacitor of the modulation unit 26 can be charged to a value of the start voltage V_start. When the user starts to run on the sporting apparatus 2, the electricity generating unit 23 is in low speed so that the generated electricity is lower than the start voltage V_start of the capacitor. In this case, the electricity generating unit 23 does not output the armature current Ia, so that the counter torque of the electricity generating unit 23 is not induced. Accordingly, the user can feel that the load for running on the endless belt 22 is lower, so the user can easily drive the endless belt 22 to rotate. After the endless belt 22 is rotated, the electricity generating unit 23 starts to output the electricity to the load.

In other aspects, the electricity generating unit 23 can be used as a start motor (not shown). In more specific, when the user starts to run on the sporting apparatus 2, the current is generated and flows into the electricity generating unit 23 so as to drive the electricity generating unit 23 to rotate. Accordingly, the endless belt 22 is driven to rotate. This configuration can also make the user feel it is easy to run on the endless belt 22.

FIG. 6 is a flow chart of a control method of the sporting apparatus 2 according to the embodiment of the invention. The control method of the sporting apparatus 2 includes the following steps of: sensing a position of a user on the endless belt 22 so as to generate a sensing signal SS (step S01), adjusting the armature current Ia according to the sensing signal SS (step S02), and controlling a rotation speed of the endless belt 22 according to the armature current Ia (step S03). In this embodiment, the step S01 of sensing the position of the user on the endless belt 22 so as to generate the sensing signal SS is performed by a position sensing unit 24. The step S02 of adjusting the armature current Ia according to the sensing signal SS is performed by a modulation unit 26. Accordingly, the rotation speed of the endless belt 22 can be changed so as to keep the user at a specific position on the endless belt 22. In addition, the rotation speed of the endless belt 22 increases when the armature current Ia decreases; on the contrary, the rotation speed of the endless belt 22 decreases when the armature current Ia increases.

The other elements of the sporting apparatus 2 and their technical features are described hereinabove, so the detailed description thereof is omitted.

In summary, the sporting apparatus of the invention is configured with an electricity generating unit for transforming kinetic energy transmitted from the endless belt into electric power, and a position sensing unit for sensing a position of a user on the endless belt so as to generate a sensing signal. Furthermore, the armature current of the electricity generating unit can be adjusted for controlling a rotation speed of the endless belt. Therefore, the sporting apparatus does not need the external power and can adjust the rotation speed of the endless belt according to the position of the user on the endless belt. Accordingly, the user can be kept on the specific position of the endless belt so as to protect the user from falling down and getting hurt due to that the running speed of the user does not compete with the rotation speed of the endless belt. As a result, in the sporting apparatus and control method thereof of the invention, the external power is not necessary and the user can be protect from falling down and getting hurt.

Although the present invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the present invention.

Claims

1. A sporting apparatus, comprising: a structure body;an endless belt disposed on the structure body;an electricity generating unit disposed in the structure body and transforming kinetic energy transmitted from the endless belt into electric power; anda position sensing unit disposed in the structure body and sensing a position of a user on the endless belt so as to generate a sensing signal, wherein an armature current of the electricity generating unit is adjusted for controlling a rotation speed of the endless belt.

2. The sporting apparatus according to claim 1, further comprising: a transmission mechanism disposed in the structure body and connected with the endless belt and the electricity generating unit.

3. The sporting apparatus according to claim 1, further comprising: a modulation unit electrically connected with the electricity generating unit and the position sensing unit, wherein the modulation unit controls the armature current according to the sensing signal.

4. The sporting apparatus according to claim 3, wherein the modulation unit adjusts the armature current according to the sensing signal for changing the rotation speed of the endless belt, so that the user is kept on a specific position of the endless belt.

5. The sporting apparatus according to claim 3, wherein the modulation unit controls the armature current by pulse width modulation.

6. The sporting apparatus according to claim 3, wherein the modulation unit controls the armature current by modulating an output power of the electricity generating unit.

7. The sporting apparatus according to claim 1, further comprising: at least a piezo-electric element disposed in the endless belt.

8. The sporting apparatus according to claim 1, further comprising: a start auxiliary unit electrically connected with the electricity generating unit, wherein the start auxiliary unit provides a start voltage.

9. A control method applied to a sporting apparatus, wherein the sporting apparatus comprises an endless belt, and the endless belt rotates to drive an electricity generating unit to generate an armature current, the method comprising the following steps of: sensing a position of a user on the endless belt so as to generate a sensing signal;adjusting the armature current according to the sensing signal; andcontrolling a rotation speed of the endless belt according to the armature current.

10. The method according to claim 9, wherein the step of sensing the position of the user on the endless belt so as to generate the sensing signal is performed by a position sensing unit.

11. The method according to claim 9, wherein the step of adjusting the armature current according to the sensing signal is performed by a modulation unit.

12. The method according to claim 11, wherein the modulation unit controls the armature current by pulse width modulation.

13. The method according to claim 11, wherein the modulation unit controls the armature current by modulating an output power of the electricity generating unit.

14. The method according to claim 11, wherein the modulation unit alters the armature current so as to change the rotation speed of the endless belt, so that the user is kept on a specific position of the endless belt.

15. The method according to claim 9, wherein when the armature current decreases, the rotation speed of the endless belt increases.

16. The method according to claim 9, wherein when the armature current increases, the rotation speed of the endless belt decreases.