Electricity: motive power systems – Automatic and/or with time-delay means
Reexamination Certificate
2001-03-30
2002-10-01
Hsieh, Shih-Yung (Department: 2837)
Electricity: motive power systems
Automatic and/or with time-delay means
C318S132000, C318S254100, C318S362000, C318S369000, C318S371000, C318S373000, C318S375000, C318S376000, C318S383000, C318S280000, C318S283000, C198S571000, C198S577000, C198S781080
Reexamination Certificate
active
06459224
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zone control method in a roller conveyor which can be suitably applied to a roller conveyor system, and a zone controller.
2. Background Art
An example of conventional roller conveyor systems is one disclosed in JP-A-11-199030 so constructed that a conveyance line is divided into a plurality of control zones, and a zone controller is provided for each of the control zones, to perform zero pressure accumulation (ZPA) type conveyance by zone control.
In the conventional conveyor system, a conveying motor roller and a free roller are provided for each zone, the motor roller and the free roller are connected to each other by a hanging belt wound around each other, and a photoelectric switch for detecting load presence and a zone controller (a drive board) for driving the motor roller are provided for the zone. Each of the zone controllers is so constructed as to rotate and stop the motor roller in response to a load presence signal detected by the photoelectric switch, a driving command signal from the drive board in the upstream zone, and a conveying state signal from the zone controller in the downstream zone.
In order to stop the motor roller, a short-circuit brake is generally used.
When the motor roller is braked by the short-circuit brake, however, a braking torque is approximately constant. Accordingly, the number of rotations of the motor roller until the roller is completely stopped varies, and the position where a conveyed article is stopped, which hereinafter may be called “the actual stop position”, is not determined depending on the magnitude of an inertial force due to the difference in the weight of the article. Further, the larger the weight of the conveyed article is, the larger the amount of slip of the article with respect to the roller in a case where the roller is stopped is. This makes it difficult to control the position where the roller is stopped.
FIG. 8
is a pulse waveform diagram showing a rotational pulse signal by a motor contained in a motor roller in a case where only a box containing no product is conveyed and is stopped by a short-circuit brake.
FIG. 9
is a pulse waveform diagram showing the rotational pulse signal in a case where a product having a weight of 30 kgf is contained in the box, and the box is conveyed and is stopped by the short-circuit brake. The rotational pulse signal is one in which two pulses are generated every time the motor rotates once, and is generated from an output signal of a magnetic pole position detector such as a Hall element of the motor. The motor roller contains a decelerator with a deceleration ratio of 1 to 11, and is so constructed as to rotate once when the motor rotates 11 times. 22 pulses are generated in the pulse signal every time the motor roller rotates once. It is assumed that the circumferential length of the motor roller is approximately 120 mm. If no slip occurs, the box shall be conveyed by (120/22=) 5.45 mm for each of pulses composing the rotational pulse signal.
As shown in
FIG. 8
, when only the box is conveyed, it is stopped after an elapse of three pulses since the short-circuit brake was started. The position where the box is stopped is spaced 136 mm apart from the position where the short-circuit brake is started. The amount of slip is (136−3×5.45=) 120 mm. On the other hand, when the product having a weight of 30 kgf is conveyed, as shown in
FIG. 9
, the box is stopped after an elapse of 16 pulses since the short-circuit brake was started. The position where the box is stopped is spaced 1110 mm apart from the position where the short-circuit brake was started. The amount of slip is (237−16×5.45=) 150 mm.
In a case where the position where the box is stopped thus varies depending on the weight of the conveyed article, when the motor roller is started again to start the conveyance, a time period elapsed until the conveyed article is moved to the subsequent zone differs. Accordingly, zero pressure accumulation type conveyance is interfered with. Therefore, smooth conveyance cannot be performed. Further, the conveyed articles may collide with each other unless a clearance is given between the articles.
SUMMARY OF THE INVENTION
An object of the present invention is to make it possible to stop, in a roller conveyor system for carrying out zone control, a conveyed article at an approximately constant position without varying the position where the article is stopped in a desired control zone even if the weight of the article varies.
In order to attain the above-mentioned object, the present invention takes the following technical measures.
Specifically, the present invention is directed to a roller conveyor system for carrying out zone control, characterized in that in stopping an article in a predetermined control zone, such stop control is carried out that the conveyed article is stopped with high precision at a predetermined stop position by decelerating and stopping a motor in a plurality of braking systems. Consequently, it is possible to perform a stable zero pressure accumulation operation and separate articles. Accordingly, highly precise positioning is allowed irrespective of the weight of the article. Therefore, it is easy to read and classify the articles.
Preferably, a load presence sensor is provided at the center in the direction of conveyance of the control zone, thereby making it possible to carry out the stop control irrespective of whether the direction of conveyance is a forward direction or a reverse direction. Further, it is possible to set the stop position on the basis of the number of pulses composing a rotational pulse signal which is proportional to the number of rotations of the motor. Even if the stop control is started from a certain point at a certain distance to the predetermined stop position, therefore, the conveyed article can be accurately stopped at the predetermined stop position with relatively high precision. Further, the precision of the stop position can be enhanced while decreasing the number of sensors.
A motor is an electric equipment for converting electrical energy (electric power) into mechanical energy (mechanical power), and such state is an electrically-driven state. However, the motor becomes a generator or a brake in its connected state depending on its manner of use. An electricity-generating state, an electrically-driven state and a braking state are generally called three states of the motor.
In a self-excited drive motor having a predetermined main magnetic flux, for example, a DC motor or a blushless motor, the three states of the motor are defined as follows. That is, the electricity-generating state is a state where mechanical power is converted into electric power at the power supply (that is, a state where when a rotor is rotated at a speed of not less than no-load angular velocity (generally zero) by an external force, a part of the mechanical power supplied to the rotor is outputted as electric power). The electrically-driven state is a state where electric power is converted into mechanical power and the mechanical power is applied to a load (that is, a state where when a positive constant torque load which is not more than a starting torque is connected to a rotor, a part of electric power supplied to the motor is applied to the load as mechanical power). The braking state is a state where a braking function is produced in a rotor by consuming mechanical power and electric power (that is, a state where when a rotor is rotated in the reverse direction by an external force, both mechanical power applied to the rotor and electric power applied by the power supply are consumed by a resistor of a motor armature circuit and converted into heat).
A motor braking system can be switched by switching the state of the motor. In the case of the electrically-driven state, mechanical power is applied to a load (a conveyed article). However, a part of switching of the braking system in the present invention may i
Itoh Kazuo
Kujihashi Yoshiyuki
Tachibana Toshiyuki
Hsieh Shih-Yung
Itoh Electric Company Limited
Smith Tyrone
Wood Phillips Katz Clark & Mortimer
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