WO2005067401A2

WO2005067401A2 - Parking apparatus with failure-free transfer of pallet between lift and cart, and control method for the same

Info

Publication number: WO2005067401A2
Application number: PCT/KR2005/000110
Authority: WO
Inventors: Seong Joon Kim
Original assignee: Otis Elevator Company
Priority date: 2004-01-15
Filing date: 2005-01-13
Publication date: 2005-07-28
Also published as: CN1910331A; HK1100688A1; WO2005067401A3; KR20050075127A; KR100581623B1; CN100460619C

Abstract

The present invention provides a parking apparatus comprising a pallet on which a vehicle rests, a lift moving in a vertical direction with the pallet on top thereof, a lift driving unit for raising and lowering the lift, a cart moving in a horizontal direction with the pallet on top thereof, a transfer unit for transferring the pallet between the lift and the cart, a lift level detector for detecting an arrival of the lift in a transfer level in which the pallet can be transferred between the lift and the cart, a first transfer completion detector for detecting a completion of transfer of the pallet to the cart form the lift, a second transfer completion detector for detecting a completion of transfer of the pallet to the lift from the cart, and a controller sending the lift driving unit a signal for raising the lift in case that the completion of transfer of the pallet to the cart form the lift is not detected by the first transfer completion detector in a given time interval after the controller sends the transfer unit a signal for triggering the transfer of the pallet to the cart form the lift, and the controller sending the lift driving unit a signal for lowering the lift in case that the completion of a transfer of the pallet from the cart to the lift is not detected by the second transfer completion detector in a given time interval after the controller sends the transfer unit a signal for triggering the transfer of the pallet from the cart to the lift.

Description

PARKING APPARATUS WITH FAILURE-FREE TRANSFER OF PALLET BETWEEN LIFT AND CART, AND CONTROL METHOD FOR THE SAME

TECHNICAL FIELD The present invention generally relates to a parking apparatus and a pallet control method, and more particularly to a parking apparatus which can automatically resolve a transfer failure of a pallet between a lift and a cart caused by a difference in the level therebetween. The present invention further relates to a method of controlling the transfer of the pallet in the parking apparatus.

BACKGROUND ART A parking apparatus using a car-elevator includes a lift for raising or lowering a pallet on which a vehicle is carried. It further includes a cart for horizontally moving the pallet transferred from the lift toward a parking space. In Fig. 1, there is shown a parking apparatus of prior art. The parking apparatus includes a lift 1, a pallet 3 mounted upon the lift 1, and a cart 2 positioned on a parking area adjacent a shaft way for the lift 1. Lift 1 is equipped with a plurality of sensors. Front stop lift-sensor 4, front deceleration lift-sensor 5, rear deceleration lift-sensor 6 and rear stop lift-sensor 7 are provided for controlling the position of pallet 3 on lift 1. Further, upper level sensor 9 and lower level sensor 10 are also provided in lift 1 to control the position of lift 1. Cart 2 is also equipped with a plurality of sensors for controlling the position of pallet 3 on cart 2 (i.e., front stop cart-sensor 14, front deceleration cart-sensor 15, rear deceleration cart-sensor 16, and rear stop cart-sensor 17). In the prior art parking apparatus constructed in the above manner, the transfer of pallet 3 from lift 1 to cart 2 is performed in the following manner. When a control signal for transferring the pallet 3 from lift 1 to cart 2 is emitted, pallet 3 is first transferred at a high speed by rotation of driving unit provided in lift 1. The driving unit is also provided in cart 2. When front deceleration cart-sensor 15 detects pallet 3 that is moved at a high speed, then a controller (not shown) sends a signal to the driving unit for reducing the rotational speed thereof. This is so that the pallet 3 begins to move at a low speed. The controller stops the driving unit upon receiving a signal from front stop cart-sensor 14, which emits the signal when it detects pallet 3. However, as shown in Fig. 2, the prior art has a shortcoming in that if lift 1 stays at a lower level than cart 2, then the complete transfer of pallet 3 to cart 2 often fails. This is because the rear wheel 3b of pallet 3, which moves at a reduced speed, cannot climb up the step to cart 2, which is at a higher level than lift 1. In such situation, if the controller does not receive a signal from front stop cart-sensor 14, which emits the signal when it detects pallet 3, within a given time period, the controller determines that a problem has occurred in the parking apparatus. Thus, it stops the whole operation of the parking apparatus so that the above problem must be manually solved by the operators. Further, when transferring the pallet 3 to lift 1, if lift 1 is at a higher level than cart 2, then the complete transfer of pallet 3 to lift 1 often fails as the pallet 3 is caught by the step. In this respect, the controller determines that there is a problem in the parking apparatus and stops the whole apparatus so that the problem also has to be solved manually. As described above, in the prior art parking apparatus, shutting down the parking apparatus is the only emergency procedure when the transfer of the pallet fails due to a level difference between the lift and the cart, in which such failure must be resolved manually by the operators. Therefore, a plurality of operators is necessary to manually fix the problem. Further, since the apparatus is inoperative during the fixing process, an increased amount of time has to be spent by the user.

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a parking apparatus, which can automatically solve a transfer failure of a pallet caused by a difference in the level between a lift and a cart. In addition, it is a further object of the present invention to provide a method for controlling the transfer of the pallet. The object and other objects of the present invention can be achieved by providing a parking apparatus comprising: a pallet on which a vehicle rests; a lift moving in a vertical direction with the pallet disposed thereon; a lift driving unit for raising and lowering the lift; a cart moving in a horizontal direction with the pallet disposed thereon; a transfer unit for transferring the pallet between the lift and the cart; a lift level detection means for detecting an arrival of the lift in a transfer level in which the pallet can be transferred between the lift and the cart; a first transfer completion detecting means for detecting a completion of transfer of the pallet to the cart from the lift; a second transfer completion detecting means for detecting a completion of transfer of the pallet to the lift from the cart; and a controller for sending a signal to the lift driving unit for raising the lift in case said completion of transfer of the pallet to the cart from the lift is not detected by the first transfer completion detecting means in a given time interval after the controller sends the transfer unit a signal for triggering the transfer of the pallet to the cart from the lift, the controller further being adapted to send a signal to the lift driving unit for lowering the lift in case said completion of a transfer of the pallet from the cart to the lift is not detected by the second transfer completion detecting means in a given time interval after the controller sends the transfer unit a signal for triggering the transfer of the pallet from the cart to the lift. According to one aspect of the present invention, the lift level detection means comprises an upper sensor mounted on a portion of the lift facing the cart 2 and generating a first signal when the cart exists in front of the upper sensor while generating a second signal, and a lower sensor mounted on a portion of the lift facing the cart 2 and being separated from the upper sensor in a vertical direction, the lower sensor generating a first signal when the cart exists in front of the lower sensor while generating a second signal, wherein the upper sensor and the lower sensor generate the first signal when the lift is in the transfer level. According to another aspect of the present invention, in case of sending said signal for raising the lift, the controller further sends a signal for stopping the raising of the lift upon receiving the second signal from the upper sensor, and in case of sending said signal for lowering the lift, the controller further sends a signal for stopping the lowering of the lift upon receiving the second signal from the lower sensor. According to another aspect of the present invention, the first transfer completion detecting means comprises a stop cart-sensor generating a first signal when the pallet exists in front of the stop cart-sensor while generating a second signal, the stop cart-sensor being mounted on the cart such that it generates the first signal when the transfer of the pallet to the cart is completed. According to another aspect of the present invention, the first transfer completion detecting means further comprises a deceleration cart-sensor generating a first signal when the pallet exists in front of the deceleration cart-sensor while generating a second signal, the deceleration cart-sensor being mounted on the cart such that it informs the controller of a time point at which the pallet should be decelerated to a low speed before the transfer of the pallet to the cart is completed. According to another aspect of the present invention, the controller checks for an elapse of the given time interval by starting a counting of an elapsed time at the time when said deceleration cart-sensor generates the first signal. According to another aspect of the present invention, the second transfer completion detecting means comprises a stop lift-sensor for generating a first signal when the pallet exists in front of the stop lift-sensor while generating a second signal, the stop lift-sensor being mounted on the lift such that it generates the first signal when the transfer of the pallet to the lift is completed. According to another aspect of the present invention, the second transfer completion detecting means further comprises a deceleration lift-sensor for generating a first signal when the pallet exists in front of the deceleration lift-sensor while generating a second signal, the deceleration lift-sensor being mounted on the lift such that it informs the controller of a time point at which the pallet should be decelerated to a low speed before the transfer of the pallet to the lift is completed. According to another aspect of the present invention, the controller checks for an elapse of the given time interval by starting a counting of an elapsed time at the time when said deceleration lift-sensor generates the first signal. According to another aspect of the present invention, the sensors are direct- reflection type optoelectronic sensors. According to another aspect of the present invention, there is provided a method of controlling a transfer of a pallet in a parking apparatus comprising the pallet on which a vehicle rests, a lift moving in a vertical direction with the pallet disposed thereon, and a cart moving in a horizontal direction with the pallet disposed thereon, the method comprising the steps of: a) allowing the lift to arrive at a transfer level at which the pallet can be transferred between the lift and the cart by raising or lowering the lift; b) raising the lift in case the transfer of the pallet to the cart from the lift is not completed in a given time interval after the transfer of the pallet to the cart from the lift is triggered; and c) lowering the lift in case the transfer of the pallet to the lift from the cart is not completed in a given time interval after the transfer of the pallet to the lift from the cart is triggered.

BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a top plan view of a lift, a cart and a pallet of the prior art parking apparatus; Fig. 2 is a side elevational view showing a transfer failure of the pallet due to a level difference between the lift and the cart of the prior art parking apparatus; Fig. 3 is a front elevational view of a lift and a pallet of a parking apparatus constructed in accordance with the present invention; Fig. 4 is a side elevational view of the lift and the pallet shown in Fig. 3; Figs. 5 and 6 are side elevational views showing a transfer of the pallet from the lift to the cart in the parking apparatus of the present invention; and Figs. 7 and 8 are side elevational views showing a transfer of the pallet from the cart to the lift in the parking apparatus of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Herein below, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. Figs. 3 and 4 are a front elevational view and a side elevational view, respectively, of lift 1, cart 2 and pallet 3 of a parking apparatus constructed in accordance with the present invention. Lift 1 is a member adapted to vertically travel through a shaft way (not shown), thus raising and lowering pallet 3 on which a vehicle can be carried. For the vertical travel of lift 1, a lift-driving unit (not shown) is mounted adjacent to the shaft way in order to raise and lower lift 1. Pallet 3 includes wheels 3a, 3b, i.e., a pair of front wheels 3a mounted on a lower surface of a front end and a pair of rear wheels 3b mounted on a lower surface of a rear end, and driven bar 3c formed on a lower surface along a center line. Driven bar 3 c is a member enabling a transfer of pallet 3 by being disposed between transfer rollers lc, 2c, which are mounted on lift 1 and cart 2, respectively. Lift 1 includes on its upper surface a pair of transfer rails la adapted to engage with wheels 3a, 3b of pallet 3, a transfer unit, sensors 6, 7 for detecting a position of pallet 3, and sensors 9, 10 mounted on a lateral surface of lift 1 facing cart 2 to detect a level of lift 1. The transfer unit is provided with a pair of transfer rollers lc which can grasp driven bar 3 c therebetween, base lb supporting the pair of transfer rollers lc, and a driving motor (not shown) for rotating the pair of transfer rollers lc. Deceleration lift-sensor 6 serves to inform a controller (not shown) of a time point at which a speed of pallet 3, which initially moves at a high speed, has to be changed to a low speed in the transfer of pallet 3. In other words, when deceleration lift-sensor 6 detects pallet 3, the controller adjusts a rotational speed of the driving motor to allow pallet 3 to be transferred at a low speed. Stop lift-sensor 7 serves to inform the controller of a complete arrival of pallet 3 onto lift 1 in a transfer of pallet 3 to lift 1 from cart 2. Cart 2 includes a pair of transfer rails 2a that is formed on an upper surface of cart 2 and aligned with transfer rails la of lift 1, a transfer unit, stop cart-sensor 14 and deceleration cart-sensor 15 for detecting the position of pallet 3 on cart 2. The transfer unit of cart 2, which has a configuration substantially similar to that of lift 1, is provided with a driving motor, a base and a pair of transfer rollers 2c. The transfer unit of cart 2 is adapted to grasp driven bar 3 c and serves to move pallet 3 toward cart 2 or lift 1 by cooperating with the transfer unit of lift 1. Deceleration cart-sensor 15 serves to inform the controller of a time point at which a speed of pallet 3, which initially moves at a high speed, has to be changed to a low speed in the transfer of pallet 3 from lift 1 to cart 2. In other words, when deceleration cart-sensor 15 detects pallet 3, the controller adjusts a rotational speed of the driving motor to allow pallet 3 to be transferred at a low speed. Stop cart- sensor 14 serves to inform the controller of a complete arrival of pallet 3 onto cart 2 in the transfer of pallet 3 from lift 1 to cart 2. As to the sensor that can be used in the present invention, a direct-reflection type optoelectronic sensor is preferable, which includes, as one-pieced device, a light emitter for emitting a light and a light receiver for receiving the light emitted from the light emitter and then reflected from an object existing (e.g., in front of the sensor). Each of the sensors for detecting the position of pallet 3 generates ON- signal when it detects the light emitted from its light emitter and then reflected from pallet 3 passing by in front of the sensor, while otherwise generating Off-signal. Upper level sensor 9 and lower level sensor 10 are needed to allow vertically traveling lift 1 to arrive at a transfer level at which pallet 3 can be transferred between lift and cart 2. Each of these sensors generates ON-signal when only cart 2 exists in front of it, while otherwise generating Off-signal. Upper level sensor 9 informs the controller of a time point at which a speed of lift 1 , which initially moves at a high speed, has to be changed to a low speed in an upward movement of lift 1 toward the transfer level. When upper level sensor 9 is switched ON, the controller sends the lift- driving unit a signal for changing the rising speed of lift 1 to a low speed. When lower level sensor 10 generates the ON-signal and the controller receives the signal, the controller sends the lift-driving unit a signal for stopping lift 1 that is moved at a low speed. On the contrary, when lift 1 approaches the transfer level during its downward movement, lower level sensor 10 serves to inform the controller of a time point for deceleration at which lift 1, which initially moves at a high speed, has to be decelerated to a low speed, hi other words, when lower level sensor 10 is switched ON, the controller sends the lift-driving unit a signal for changing the lowering speed of lift 1 to a low speed. When upper level sensor 9 generates the ON-signal, the controller sends the lift-driving unit a signal for stopping lift 1 that is moved at a low speed. Referring to Figs. 5 and 6, the operation of the parking apparatus of the present invention will now be described by exemplifying the transfer of pallet 3 from lift 1 to cart 2. When the lift 1 with pallet 3 on which the vehicle is loaded upwardly moves at a high speed to approach the transfer level and the upper level sensor 9 is switched ON, the controller sends the lift-driving unit a signal for reducing the rising speed of lift 1. The controller further sends the lift-driving unit a signal for stopping the lift 1 when lower level sensor 10 is also switched ON. At such time, both the upper level sensor 9 and lower level sensor 10 are in ON-state. In case the lift 1 approaches the transfer level during its downward movement, lower level sensor 10 serves to inform the controller of the time point for deceleration, while upper level sensor 9 serves to inform the controller of the arrival of pallet 3 at the transfer level. Next, when the controller emits a signal for triggering the transfer of pallet 3 from lift 1 to cart 2 from the controller, transfer rollers lc, 2c are rotated at a high speed in a direction for moving pallet 3 from lift 1 to cart 2. Driven bar 3c is linearly moved by the rotation of the pair of transfer rollers lc and, therefore, pallet 3 begins to be transferred from lift 1 to cart 2 at a high speed. Upon receiving the ON-signal from deceleration cart-sensor 15, the controller controls the driving motor, which is connected to the transfer rollers lc, 2c, in order to reduce the speed of pallet 3 being transferred to cart 2. At the same time, the controller starts to count the time elapse by using a timer (not shown) from the moment it receives the ON-signal from deceleration cart-sensor 15. If stop cart- sensor 14 does not generate ON-signal even after the elapsed time exceeds a given time period, the controller assumes that the transfer of pallet 3 has failed (since lift 1 is at a lower level than cart 2) with a step being made between lift 1 and cart 2, in which the wheels of pallet 3 do not climb up the step to cart 2. Next, the controller performs a level-correction procedure for completing the transfer of pallet 3. Although the counting of the elapsed time is started at the time the controller receives the ON-signal from deceleration cart-sensor 15 in the preferred embodiment, various modifications are available. For example, the counting of the elapsed time may begin at the time when the controller sends the signal for rotating the transfer rollers lc, 2c, or at the time when the controller receives OFF-signal from deceleration lift-sensor 6 or stop lift-sensor 7. In other words, the counting of the elapsed time may be started at different time points. Therefore, the given time period may have different values depending upon the selected time points and can be determined by considering the time period data obtainable by measurements in a real pallet transfer process in which no transfer failure of pallet 3 occurs. For example, time period data may be a time period between the moment when the controller sends the signal for rotating the transfer rollers lc, 2 and the moment when stop cart- sensor 14 generates the ON-signal, or a time period between the moment when the controller receives the OFF-signal from deceleration lift-sensor 6 or stop lift-sensor 7 and the moment when stop cart-sensor 14 generates the ON-signal. In the correction procedure, the controller raises lift 1 at a decelerated speed until upper level sensor 9 emits an OFF-signal. Since the level difference hindering the transfer of pallet 3 is removed or the destination becomes lower than lift 1 during the rising of lift 1, the transfer of pallet 3 from lift 1 to cart 2 is resumed by the continuous rotation of transfer rollers lc, 2c. Upon receiving an ON-signal from stop cart-sensor 14, the controller sends the driving motor a signal for stopping the rotation of transfer rollers lc, 2c and the transfer of pallet 3 from lift 1 to cart 2 is finished. Regarding the level-correction process of raising lift 1, various modifications are available in addition to the process used in the preferred embodiment. In one modification, the controller may be programmed to raise lift 1 at the decelerated speed only for a predetermined time period without assistance by such sensor. As such, the pallet 3 can be completely transferred to cart 2 during the rising of lift 1 by the continuous rotation of transfer rollers lc, 2c. However, the process of the modification has a shortcoming compared to the process of the preferred embodiment in that it has to be accompanied by annoying tests for determining the time period for which lift 1 is raised. Referring to Figs. 7 and 8, a process of the transfer of pallet 3 from cart 2 to lift 1 is now described. Under a situation where lift 1 moves upwardly at a high speed to approach the transfer level, when upper level sensor 9 is switched ON, the controller sends the lift- driving unit a signal for reducing the rising speed of lift 1. The controller further sends the lift-driving unit a signal for stopping the lift 1 when lower level sensor 10 is switched ON. At this time, both the upper level sensor 9 and lower level sensor 10 are in ON-state. In case the lift 1 approaches the transfer level during its downward movement, lower level sensor 10 informs the controller of the time point for deceleration and the controller stops the downward movement of lift 1 upon receiving an ON-signal from upper level sensor 9. Next, when the controller emits a signal for triggering the transfer of pallet 3 from cart 2 to lift 1, transfer rollers lc, 2c are rotated at a high speed in a direction for moving pallet 3 from cart 2 to lift 1. Driven bar 3c is linearly moved by the rotation of the pair of transfer rollers lc. Therefore, pallet 3 begins to be transferred from cart 2 to lift 1 at a high speed. Upon receiving the ON-signal from the deceleration lift-sensor 6, the controller controls the driving motor, which is connected to the transfer rollers lc, 2c, in order to reduce the speed of pallet 3 being transferred. At the same time, the controller starts counting the time elapsed from the moment it receives the ON-signal from deceleration lift-sensor 6 by using the timer. If stop lift-sensor 7 does not generate an ON-signal even after the elapsed time exceeds a given time period, the controller assumes that the transfer of pallet 3 has failed (since lift 1 is at an upper level than cart 2), thus making a step between lift 1 and cart 2 while the wheels of pallet 3 do not climb up the step to lift 1. Next, the controller performs a level- correction procedure for completing the transfer of pallet 3. As previously mentioned in the description regarding the transfer of pallet 3 from lift 1 to cart 2, the counting of the elapsed time may begin at the time when the controller sends the signal for rotating the transfer rollers lc, 2c, or at the time when the controller receives OFF-signal from deceleration cart-sensor 15 or stop cart- sensor 14. In other words, the counting of the elapsed time may be started at different time points. Therefore, the given time period may have different values depending upon the selected time points and can be determined by considering the time period data measured in tests in which no transfer failure of pallet 3 occurs. For example, time period data may be a time period between the moment when the controller sends the signal for rotating the transfer rollers lc, 2 and the moment when stop lift-sensor 7 generates the ON-signal, or a time period between the moment when the controller receives the OFF-signal from deceleration cart-sensor 15 or stop cart-sensor 14 and the moment when stop lift-sensor 7 generates the ON-signal. hi the level-correction procedure, the controller lowers lift 1 at a decelerated speed until lower level sensor 10 emits an OFF-signal. Since the level difference hindering the transfer of pallet 3 is removed or the destination becomes lower than cart 2 during the downward movement of lift 1, the transfer of pallet 3 from cart 2 to lift 1 is resumed by the continuous rotation of transfer rollers lc, 2c. Upon receiving an ON-signal from stop lift-sensor 7, the controller sends a signal to the driving motor for stopping the rotation of transfer rollers lc, 2c and the transfer of pallet 3 from cart 2 to lift 1 is finished. Regarding the level-correction process of lowering lift 1, various modifications are available in addition to the process used in the preferred embodiment, hi one modification, the controller may be programmed to lower lift 1 at the decelerated speed only for a predetermined time period (not being assisted by such sensor). The process of the present invention for resolving the transfer failure due to the level difference between the lift and the cart can be summarized as follows. First, lift 1 is lowered or raised to approach the transfer level at which pallet 3 can be transferred between lift 1 and cart 2. Next, in the transfer of pallet 3 to cart 2 from lift 1, if the transfer of pallet 3 to cart 2 is not completed even after the predetermined time period, lift 1 is raised. In the transfer of pallet 3 to lift 1 from cart 2, if the transfer of pallet 3 to lift 1 is not completed even after the predetermined time period, lift 1 is lowered. Meanwhile, if the controller does not receive the ON-signal from stop cart- sensor 14 or stop lift-sensor 7 even after the rising of lift 1 or the lowering of lift 1 for correcting the level difference, the controller stops the whole operation of the parking apparatus to allow the operators to manually fix the problem. The controller may be equipped with an additional timer (not shown), hi the transfer of pallet 3 to cart 2 from lift 1, the additional timer counts elapsed time from the moment when upper level sensor 9 generates the OFF-signal during the upward level correction of lift 1. hi the transfer of pallet 3 to lift 1 from cart 2, the . additional timer counts elapsed time from the moment when lower level sensor 10 emits the OFF-signal during the downward level correction movement of lift 1. The controller is programmed to stop the whole operation of the parking apparatus when it does not receive the ON-signal from stop cart-sensor 14 or stop lift-sensor 7 even after the elapsed time exceeds a given time period. The counting of the elapsed time may have different starting points of time. The given time period described above may be determined by considering the time period data obtainable by measurements in a real pallet transfer process in which the transfer of pallet 3 is completed through the transfer failure and the accompanied process of level correction of lift 1 for solving the transfer failure.

INDUSTRIAL APPLICABILITY hi accordance with the present parking apparatus and a method of controlling the transfer of the pallet, since the level difference between the lift and the cart is removed or the destination becomes lower than the departure by the upward correction movement or the downward correction movement of the lift by a predetermined magnitude by using existing sensors, the transfer failure of the pallet between the cart and the lift is remarkably reduced so that the number of operators for providing a manual solution may be reduced. Therefore, product reliability of the parking apparatus is increased.

Claims

1. A parking apparatus comprising: a pallet on which a vehicle rests; a lift moving in a vertical direction with the pallet on top thereof; a lift driving unit for raising and lowering the lift; a cart moving in a horizontal direction with the pallet on top thereof; a transfer unit for transferring the pallet between the lift and the cart; a lift level detection means for detecting an arrival of the lift in a transfer level in which the pallet can be transferred between the lift and the cart; a first transfer completion detecting means for detecting a completion of transfer of the pallet to the cart from the lift; a second transfer completion detecting means for detecting a completion of transfer of the pallet to the lift from the cart; and a controller sending the lift driving unit a signal for raising the lift in case said completion of transfer of the pallet to the cart from the lift is not detected by the first transfer completion detecting means in a given time interval after the controller sends the transfer unit a signal for triggering the transfer of the pallet to the cart from the lift, and the controller sending the lift driving unit a signal for lowering the lift in case said completion of a transfer of the pallet from the cart to the lift is not detected by the second transfer completion detecting means in a given time interval after the controller sends the transfer unit a signal for triggering the transfer of the pallet from the cart to the lift.

2. The parking apparatus of claim 1, wherein said lift level detection means comprises: an upper sensor mounted on a portion of the lift facing the cart 2 and generating a first signal when the cart exists in front of the upper sensor while generating a second signal otherwise; and a lower sensor mounted on a portion of the lift facing the cart 2, being separated from the upper sensor in a vertical direction, the lower sensor generating a first signal when the cart exists in front of the lower sensor while generating a second signal otherwise, wherein the upper sensor and the lower sensor generate the first signal when the lift is in the transfer level.

3. The parking apparatus of claim 2, wherein in the case of sending said signal for raising the lift, the controller further sends a signal for stopping the raising of the lift upon receiving the second signal from the upper sensor, and in the case of sending said signal for lowering the lift, the controller further sends a signal for stopping the lowering of the lift upon receiving the second signal from the lower sensor.

4. The parking apparatus of claim 1, wherein said first transfer completion detecting means comprises a stop cart-sensor generating a first signal when the pallet exists in front of the stop cart-sensor while generating a second signal otherwise, the stop cart-sensor mounted on the cart such that it generates the first signal when the transfer of the pallet to the cart is completed.

5. The parking apparatus of claim 4, wherein said first transfer completion detecting means further comprises a deceleration cart-sensor generating a first signal when the pallet exists in front of the deceleration cart-sensor while generating a second signal otherwise, the deceleration cart-sensor mounted on the cart such that it informs the controller of a time point at which the pallet should be decelerated to a low speed before the transfer of the pallet to the cart is completed.

6. The parking apparatus of claim 5, wherein said controller checks an elapse of the given time interval by starting a counting of an elapsed time at the time when said deceleration cart-sensor generates the first signal.

7. The parking apparatus of claim 1, wherein said second transfer completion detecting means comprises a stop lift-sensor generating a first signal when the pallet exists in front of the stop lift-sensor, while generating a second signal otherwise, the stop lift-sensor mounted on the lift such that it generates the first signal when the transfer of the pallet to the lift is completed.

8. The parking apparatus of claim 7, wherein said second transfer completion detecting means further comprises a deceleration lift-sensor generating a first signal when the pallet exists in front of the deceleration lift-sensor, while generating a second signal otherwise, the deceleration lift-sensor mounted on the lift such that it informs the controller of a time point at which the pallet should be decelerated to a low speed before the transfer of the pallet to the lift is completed.

9. The parking apparatus of claim 8, wherein said controller checks an elapse of the given time interval by starting a counting of an elapsed time at the time when said deceleration lift-sensor generates the first signal.

10. The parking apparatus of one of claims 2 through 9, wherein said sensors are of a direct-reflection type optoelectronic sensor.

11. A method of controlling a transfer of a pallet in a parking apparatus provided with the pallet on which a vehicle rests, a lift moving in a vertical direction with the pallet on top thereof, and a cart moving in a horizontal direction with the pallet on top thereof, the method comprising the steps of: a) allowing the lift to arrive at a transfer level at which the pallet can be transferred between the lift and the cart, by raising or lowering the lift; b) raising the lift in case that the transfer of the pallet to the cart from the lift is not completed in a given time interval after the transfer of the pallet to the cart from the lift is triggered, and c) lowering the lift in case that the transfer of the pallet to the lift from the cart is not completed in a given time interval after the transfer of the pallet to the lift from the cart is triggered.