BACKGROUND Elevator cars are typically moved by a hoist motor and the car doors are opened and closed by a door motor. The proper voltage and frequency current is provided by a hoist mo- tor inverter to the hoist motor based on instructions from a hoist motor controller, and the proper voltage and frequency current is provided to the door motor by a door motor inverter based on command input from a door motor controller.

There are instances where the hoist motor and the door motor are operated simultane- ously to increase a car's operating efficiency. For example, immediately before the car reaches or leaves a floor, the door motor is driven along with the hoist motor. Also, releveling (aligning the floor of the car with the floor at the entrance) may be performed while doors are opened.

Thus, while high performance, general-use elevators may require that the hoist motor and the door motor be driven simultaneously to increase operating efficiency, certain home elevator applications do not require high operating efficiency. For such elevators, the need to provide separate hoist motor inverters and door motor inverters has contributed to the cost of the product.

What is needed is a means for decreasing the overall cost of a home elevator, or the like.

SUMMARY OF THE INVENTION In order to accomplish this purpose, this invention is equipped with a hoist motor that moves a car, a door motor that opens and closes the car door or doors, an inverter section that simultaneously controls the voltage and frequency of the current provided to the hoist motor and the door motor, and a control section that sends instructions to this inverter section to control the speed at which the car travels and the speed at which the door opens and closes. It is constituted so that the proper voltage and frequency current will be provided to the hoist motor from the inverter section until the car reaches a floor; and, after the car reaches a floor, the proper voltage and frequency will then be provided to the door motor from the same inverter section.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a block diagram that shows one application example of an elevator associated with this invention.

DETAILED DESCRIPTION Referring to Figure 1, elevator car 1 is driven in a hoistway (not shown) and includes a horizontally sliding door 5 driven by door operator motor 6. The car 1 is positioned verti- cally by means of a rope 2 attached to the car 1 and suspended from the elevator drive sheave 3a. The rope 2 terminates at its other end at a counter weight 4 which provides a balancing of the vertical forces on the carl. Drive sheave 3a is rotated by hoist motor 3 which turns an intermediate shaft 3b as shown.

Both the hoist motor 3 and the door motor 6 are variable voltage alternating current motors which may be precisely controlled for speed and position by varying the voltage and frequency of the supplied motor current.

According to the present invention, three phase variable frequency alternating current is supplied to either the hoist motor 3 or the door motor 6 by a controlled inverter section 8 which receives fixed voltage alternating current from a power source 7, such as an electric utility supply line. The voltage and frequency of the output current 11 from the inverter sec- tion 8 is controlled in response to the inputs from a controller 9 as shown in the figure.

During vertical movement of the elevator carl, doors 5 are closed and the inverter section 8 supplies variable frequency and voltage current to the hoist motor 3, only. The speed and position of the car 1 are controlled by the controller 9 so as to precisely deliver the elevator car, and its passengers, to the desired floor in the building served by the elevator.

Upon arriving at the desired floor level, controller door 9 causes the elevator hoist motor 3 the cease operation and initiates a signal 22 to a relay control 10 actuating the power relay 12.

Power relay 12 is operated, in response to the actuator 10, to switch the output 11 of the inverter section 8 from the hoist motor 3 to the door motor 6. After the inverter 8 is con- nected to the door motor 6, controller 9, using a completely different velocity profile, drives the door motor 6 to open the doors to permit ingress and egress of the passengers to the ele- vator car 1.

It would be appreciated by those skilled in the art that the control signals provided to the inverter 8 by the controller 9 will differ in response to the controllers selection of either the hoist motor or the door motor for receiving the inverter output 11. Thus, a single inverter 8 and controller 9 may be used to control both a hoist motor 3 and a door motor 6 in an ele- vator application. Switching relay 11 prevents the simultaneous connection of the hoist mo- tor 3 and the drive motor 6 to the inverter 8.

The system according to the present invention thus eliminates the need for a second inverter and controller as is known in the prior art, in exchange for the requirement that the single remaining inverter 8 drive only one of the hoist motor and the door motor at a given time.

In the event the elevator car were to become misleveled during a period of time in which the door motor 6 was in operation or the doors 5 in an open position, a controller 9, sensing the misleveling of the elevator with the desired floor, would direct inverter 8 to power door motor 6 so as to close doors 5, then command actuator 10 to actuate the relay 12 so as to connect the inverter 8 to the hoist motor 3 and disconnect inverter 8 from door motor 6. The controller 9 would then control the inverter 8 so as to drive hoist motor 3 to position the ele- vator car 1 at the correct position within the hoistway.

Relay 12, shown here schematically as a mechanical relay having a mechanical ac- tuator 10, may alternatively be an electronic switch or any other device or structure which can divert the output 11 of the inverter section 8 between either the hoist motor 3 or the door motor 6, in response to signal 22 from the controller 9.