Patent Application
20070253800
A travel speed pattern generation unit 50 generates a speed pattern for allowing the vehicle 4 to travel from the current position to the target position, and inputs the position in the travel direction and the travel speed of the vehicle 4 to a PID control unit 51, and a control amount by PID control is generated such that the difference from the travel speed pattern is eliminated. A vibration suppression control unit 52 filters the control amount such that the control amount in a natural vibration frequency area in the travel direction of the stacker crane 2 is eliminated or add a control amount for generating vibration in opposite phase such that natural vibration of the stacker crane 2 which may be caused at the time of acceleration and deceleration in the travel direction is offset. An output of the vibration suppression unit 52 corresponds to the total amount of torques applied to the front and rear travel motors 10, 12. For example, the PID control unit 51 generates a target acceleration and deceleration a at each time point. Alternatively, data of a signal from a position sensor in the travel direction such as the laser distance meter may be subjected to second order differentiation with respect to the time to determine the actual travel acceleration and deceleration, and the actual travel acceleration and deceleration may be used instead of the travel acceleration and deceleration a.
A torque allocation unit 53 allocates the control amount outputted from the vibration suppression unit 52 to the front and rear travel motors. The proportion is a ratio between torques generated by the front and rear travel motors 12, 10. The travel acceleration and deceleration a is inputted to the torque allocation unit 53, e.g., from the PID control unit 51. Alternatively, the travel acceleration and deceleration a may be inputted to the torque allocation unit 53 from the travel speed pattern generation unit 50. Alternatively, the distance determined by the laser distance meter 30 may be subjected to second order differentiation to determine the acceleration and deceleration. Data indicating a height position H2 of the elevation frame and the presence of any article on the elevation frame is inputted to the torque allocation unit 53. Preferably, in addition to these items of data, in order to correct the inertial force applied to the elevation frame, the acceleration and deceleration for elevation and descent a2 is inputted. In the case where the acceleration and deceleration for elevation and descent a2 of the elevation frame is considerably small in comparison with the gravitational acceleration g, e.g., in the case where the acceleration and deceleration for elevation and descent a2 is 1/10 of the gravitational acceleration g or less, the acceleration and deceleration for elevation and descent a2 is negligible. Based on these items of data, wheel pressures applied to the front and rear drive wheels, i.e., reaction forces from the travel surface such as the travel rail 3 are detected. Torques in proportion to the wheel pressures are allocated to front and rear servo mechanisms 54, 55. It is sufficient that the torques are allocated in correspondence with the wheel pressures, and it is not essential that the torques are proportional to the wheel pressures. For example, the torques should be substantially proportional to the wheel pressures. The front and rear servo mechanisms 54, 55 drive the front and rear travel motors 12, 10 by servo driving, respectively, monitor the motor current i of each of the travel motors 12, 10, and implement feedback control. For example, the motor current i is proportional to the output torque in each of the travel motors 12, 10.
It is assumed that elastic tires are used for the drive wheels 6, 8.
For balance with the moment of the inertial force −ma, the drive wheels 6, 8 are elastically deformed vertically, and the vehicle 4 is slightly inclined by an angle θ from the horizontal direction. Spring forces of the drive wheels 6, 8 generated by the inclination θ are denoted by F1, F2. The wheel pressures T1, T2 shift the spring forces from the above values by the amounts corresponding to F1, F2. Since the moment of the inertial force −ma is balanced by the moment of the spring forces F1, F2, maH=F1P1+F2P2 is obtained. Next, since the spring forces F1, F2 are expressed by F1=kP1θ, F2=kP2θ, respectively, where k is the spring constant, maH=k74 (P12+P22) is obtained. From the equation, Kθ in the spring force can be calculated. By eliminating the spring forces F1, F2, T1=mg×P2/(P1+P2)+maP1H/(P12+P22) is obtained, and likewise, T2=mg×P1/(P1+P2)−maP2H/(P12+P22) is obtained. After the wheel pressures T1, T2 are calculated, in proportion to these values, the torque allocation unit allocates the torques.
In the description, the proportion of the wheel pressures is determined assuming that elastic tires are used for the drive wheels 6, 8. In the case where elasticity of the drive wheels 6, 8 is negligible, for example, the balance between the moment of force by the gravity or the inertial force around the drive wheel 6 and the moment of force of the wheel pressure T2 applied to the drive wheel 8 should be determined. In this manner, the moment of force T2 can be determined. Likewise, from the balance between the moment of force by the gravity or the inertial force around the drive wheel 8 and the moment of force of the wheel pressure applied to the drive wheel 6, the wheel pressure T1 can be determined. Then, the torques may be allocated in proportion to the proportion of the wheel pressures.
By allocating the torques in proportion to the wheel pressures applied to the drive wheels 6, 8, the following advantages can be obtained.
(1) The torques are allocated optimally to the front and rear drive wheels.
(2) Thus, excess or deficiency does not occur in the torques. That is, idling of the drive wheel due to the excessive torque or output of “creaky” locking sounds by locking of the drive wheel due to the insufficient torque does not occur.
(3) Since locking or idling of the wheels does not occur significantly, the stacker crane can travel at a large acceleration and deceleration.
(4) Since the torques are allocated optimally, vibration of stacker crane does not occur significantly.
(5) Since the torques of the front and rear drive wheels are balanced, the amount of dust generated by the contact between the drive wheels and the travel rail is small.
In the embodiment, the stacker crane having one front wheel and one rear wheel is shown as an example. Alternatively, in the case where a stacker crane having four drive wheels including two front wheels and two rear wheels are used, in the same manner as in the case of the embodiment, the torque allocated to the front wheels is determined, and the torque is divided equally for each of the left and right front wheels (½ of the torque is allocated to each of the left and right front wheels). Likewise, the torque allocated to the rear wheels is determined, and the torque is divided equally for each of the left and right rear wheels (½ of the torque is allocated to each of the left and right rear wheels). In the case where an upper vehicle is provided additionally at the upper portion of the stacker crane, the position of the center of gravity of the vehicle by the portion other than the elevation frame should be determined in consideration of the lower vehicle, the upper vehicle, and the mast. Although the embodiment has been described in connection with the case in which the stacker crane is used, the present invention is also applicable to rail vehicles, automated guided vehicles which travel on the ground without using any rails, and in particular, suitably applicable to travel vehicles having a mast and a elevation frame.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-127257 | May 2006 | JP | national |
