The present invention relates to a non-contact power supply device for supplying electric power to a movable body running on a guide rail and to a pickup coil unit mounted on the movable body. More particularly, the pickup coil unit generates induced electromotive force based on a current along the guide rail. The electromotive force generates electric power. The electric power is supplied to the movable body through the pickup coil unit.
A transfer system including a movable body that moves along a guide rail has been proposed and is in use. This system ensures efficient distribution within a factory or a warehouse. A motor is generally used to move a movable body. The motor for moving the movable body is referred to as a drive motor. Electric power, which generally has a voltage of 200 volts, is supplied to the motor via power supply lines (trolley lines) that are laid along the guide rail.
There are two ways to supply electric power to the motor: the trolley system and the non-contact system. In the trolley system, as a collector ring provided in a movable body contacts the power supply lines, electric power is supplied to the movable body. In the non-contact system, a pickup coil is provided on a movable body at a position close to the power supply lines. This pickup coil generates induced electromotive force, and electric power is supplied to the movable body. In the trolley system, contact between a collector ring and a power supply line has a number of drawbacks. Specifically, the contact wears the collector ring and generates particulates and spark. Therefore, the collector ring must be frequently maintained. The non-contact system does not have such drawbacks. Thus, much attention has been focused on the non-contact system, which is superior to the trolley system.
For operating a movable body, electric power needs to be supplied to the drive motor for moving the movable body as well as to a control system. Further, it the movable body has loading equipment (for example, a forklift device) for loading and unloading loads, electric power must be supplied to the loading equipment. Power must also be supplied to relays for sequential control. A power system that has the drive motor and the loading equipment, relays for sequential control and the control system, which includes micro computers, requires different voltages. Specifically, the power system requires relatively high voltage, whereas computers require relatively low voltage. Thus, voltage supplied from the pickup coil is converted into different voltages, each corresponding to one of the devices.
When different voltages are required, the movable body is provided with a power supply unit 61 illustrated in FIG. 10. The power supply unit 61 includes a rectifier circuit 63, a smoothing capacitor 64 and chopper circuits 65, 66, 67. A pickup coil 62 is connected to the input terminals of the rectifier circuit 63. The chopper circuit 65, which outputs the highest voltage (for example DC 300V), is connected to a drive motor 69, with an inverter 68 located in between. The chopper circuit 66, which outputs a lower voltage (for example, DC24V) is connected to relays (not shown) for sequential control. The chopper circuit 67, which outputs the lowest voltage (for example, DC12V) is connected to a controller (not shown) having a central processing unit (CPU). The voltage generated in the single pickup coil 62 is initially rectified by the rectifier circuit 63 and then converted by the chopper circuits 65-67 into voltages required by the individual devices.
The power system and the control system in the movable body require largely different voltages. In the above described prior art movable body, the power system and the control systems share the single coil 62. The chopper circuits 65 to 67 therefore must have the same withstand voltage even if the devices connected to the chopper circuits 65 to 67 require different voltages. In other words, the chopper circuit 67, which outputs the lowest voltage, must have a high withstand voltage. This increases the cost of the chopper circuits 65 to 67. Further, since the chopper circuits 65 to 67 share the common electric power source, a surge current caused by switching of the relays affects the other systems, and noise in the power system affects the control system.
Non-contact systems have a so-called drooping characteristic, which means that the greater the output current becomes, the lower the output voltage becomes. For example, the power system of a stacker crane includes a drive motor for moving the crane and an elevator motor for elevating loads. When the crane is moved and a load is elevated simultaneously, a large amount of current is fed to the motors, while the voltage supplied to the motors is lowered. This may result in insufficient electric power for the motors.