Electric floor cleaner with a soft start function

An electric floor cleaner is of the type arranged to drive a three-phase motor, whose rated voltage is substantially equal to a voltage obtained by voltage doubling and rectifying a single-phase commercial power line and then by converting a voltage doubled d.c. voltage into three-phase a.c. by an inverter. The voltage and frequency of the three-phase a.c. output from the inverter are controlled for a predetermined period of time after a power switch is put into a turned on state from a turned off state. It is therefore possible to reduce the starting current to a small value enabling the use of a larger rated output motor than a motor in a conventional system within an allowable current limit of a commercial power line.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention generally relates to electric floor cleaners, and more 
particularly to an electric floor cleaner of the type having a three-phase 
a.c. motor driven by three-phase a.c. obtained by converting single phase 
a.c. from a single phase power source. 
2. Description of the Prior Art 
In conventional electric floor cleaners or polishers, there is a 
relationship between a brush-driving motor and power source voltage in 
theory as follows: 
(a) A system in which a two-phase 100 volt driving motor is connected to an 
output side of an inverter whose input is 100 volt and output is 100 volt. 
This system is referred to as system A. In this specification, the words 
"inverter system" are used to mean a system which converts an a.c. input 
into a d.c. by way of a rectifier, and then the d.c. is converted into a 
desired a.c., and an inverter which simply converts a.c. to d.c. is 
referred to as "inverter". 
(b) A system in which a three-phase 100 volt driving motor is connected to 
an output side of an inverter whose input is 100 volt and output is 100 
volt. This system is referred to as system B. 
(c) A system in which a single-phase 100 volt driving motor is operated 
through primary voltage control. This system is referred to as system C. 
(d) A system in which a single-phase 100 volt driving motor is driven 
directly by commercial power source This system is referred to as system 
D. 
(e) A system in which a d.c. driving motor is operated where commercial 
power is converted into d.c. by utilizing thyristors or the like. This 
system is referred to as system E. 
(f) A system in which a three-phase 200 volt driving motor is connected to 
an output side of an inverter whose input is 200 volt and output is 200 
volt where the inverter is connected to an output side of a transformer 
whose input is 100 volt and output is 200 volt. This system is referred to 
as system F. 
The above mentioned conventional systems A to F have the following 
advantages and disadvantages. 
SYSTEM A 
(DISADVANTAGES) 
Since the motor is of special type, the required frame is bulky. 
Starting current is twice the normal operation current. 
Cost is high. 
SYSTEM B 
(DISADVANTAGES) 
The inverter system is bulky. 
Transistors have control current which are large. 
A standard motor is not available. 
The size of the motor is large. 
Cost is high. 
SYSTEM C 
(DISADVANTAGES) 
The size of the motor is twice that of standard motors. 
A feedback circuit and a TG (tachometer generator) are required. 
A motor of a very special type is required. 
The starting current is large. 
Efficiency is very poor. 
(ADVANTAGES) 
The required controller is small in size. 
SYSTEM D 
(DISADVANTAGES) 
The upper limit of the motor output within the allowable current limit, 
which will be described later, is low. 
The degree of shock on starting is high. 
There are considerable magnetic vibrations. 
The starting current is large. 
Variable speed is not available. 
The size of the motor is twice that of a standard motor. 
Efficiency is very poor. 
(ADVANTAGES) 
A standard motor and standard parts can be utilized. 
Cost is low. 
SYSTEM E 
(DISADVANTAGES) 
The maintenance of carbon brushes is troublesome. 
The upper limit of the motor output is low. 
The motor is large in size. 
Cost is several times higher than other systems. 
(ADVANTAGES) 
The required controller is small in size. 
SYSTEM F 
(DISADVANTAGES) 
A large-sized transformer is required. 
(ADVANTAGES) 
A standard inverter can be used. 
Among the above described systems A to F, systems D and E are actually 
used. 
Generally, the allowable current which can be taken from a single plug 
socket or convenience outlet of a commercial power line in a building is 
20 amperes, and it is limited to disconnecting loads which require current 
more than the allowable current. 
In recent years since computers or the like are often used in building, it 
is very important to avoid power supply cut-off resulting from excess 
demand above the allowable current. Therefore, careful attention must be 
used to avoid using a polisher where the current is above a given 
allowable value. 
In the above mentioned systems D and E, it may be dangerous to use a 
driving motor of 0.75 kilowatt or more. 
In systems using a single-phase motor as system D, strong electromagnetic 
vibrations are transmitted to the hands of an operator holding a polisher 
handle, and in the worst cases, operators often suffer from an 
occupational disease due to long time use of such a polisher. 
In order to solve this problem, the present inventors invented, prior to 
the present invention, an electric floor cleaner having a three-phase 200 
volt driving motor which is driven by three-phase 200 volt a.c. obtained 
by an inverter system connected to a single-phase 100 volt power source. 
This electric floor cleaner is capable of increasing the upper limit of a 
motor's output without exceeding the allowable current limit and is also 
capable of reducing the occurrence of occupational diseases and 
undesirable influences both caused from electromagnetic vibrations. More 
specifically, this novel electric floor cleaner according to the prior 
invention is of a driving method in which a three-phase 200 volt driving 
motor is connected to an output side of an inverter system with an input 
of a single-phase 100 volt and an output of three-phase 200 volt. 
However, even if a three-phase motor is driven by producing three-phase 200 
to 240 volt power using an inverter system having a voltage doubler 
rectifier connected to a commercial power source of 100 volts to 120 
volts, and an inverter, it was only possible to increase motor output as 
high as 1.0 kilowatt within allowable current of a single plug socket of a 
single-phase commercial power source line because of the influence of 
starting current which flows on the motor starting. 
SUMMARY OF THE INVENTION 
Thus, the present invention is an improvement of the above-described 
conventional electric floor cleaner of three-phase motor driving system. 
It is therefore an object of the present invention to provide a new and 
useful electric floor cleaner which is capable of increasing motor output 
within an allowable current limit of a single-phase commercial power 
source line. 
A further object of the present invention is to provide an electrical floor 
cleaner whose starting current is minimum while the size is small and 
efficiency and power factor are the best when comparing with the 
above-mentioned systems A to F. 
A still further object of the present invention is to provide an electrical 
floor cleaner which emits less vibrations, whose cost is low, and which 
can be manufactured by using a standard motor and standard parts. 
To achieve the above objects the present invention provides: 
an electrical floor cleaner comprising: 
(a) a device for voltage doubling and rectifying a single-phase commercial 
power source voltage fed through a power switch; 
(b) an inverter for converting a voltage doubled d.c. obtained by the 
voltage doubling and rectifying device into three-phase a.c.; 
(c) a device for controlling timing of conduction of switching elements of 
the inverter so as to control voltage and frequency of the three-phase 
a.c. for a predetermined period of time after the power switch is put into 
an on state from an off state; 
(d) a three-phase motor arranged to be driven by the three-phase a.c. 
applied from the inverter, the three-phase motor having a rated voltage 
which is substantially equal to the doubled voltage; and 
(e) a floor cleaning member arranged to be driven by the three-phase motor.

The same or corresponding elements or parts are designated at like 
reference numerals throughout the drawings. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings a preferred embodiment of the electric floor 
cleaner of the present invention will be described hereinbelow. 
FIG. 1 illustrates a perspective view of an embodiment of the present 
invention. 
In the illustrated embodiment, a supporting truck 2 is attached to a tip 
portion of a handle shaft 1, and a cover 3 is attached to a front end of 
the supporting truck 2. On the upper center portion of the cover 3, is 
mounted a general purpose three-phase 200 volt motor 4. Below the cover 3, 
a rotary brush 5 is detachably attached. A gear box (not shown) for 
transmitting the rotational force of the three-phase 200 volt motor to the 
rotary brush 5 is mounted in the cover 3, and a single-phase power source 
inverter system 6 having a manipulation panel for converting single-phase 
100 volts to three-phase 200 volts is fixed to the peripheral wall of the 
motor 4. The above-mentioned three-phase 200 volt motor 4 is supplied with 
power via the single-phase power source inverter system 6 from 
single-phase 100 volt commercial power source cable 7. 
The present invention may be implemented as having vacuum suction function, 
detergent spraying function, and in such a case, a motor used for vacuum 
suction or spraying may also be supplied with power via the single-phase 
power source inverter. Furthermore, a secondary high-resistance special 
squirrel-cage stepless speed-change induction motor which is generally 
called a VC motor may be used as the three phase 200 volt motor. 
In this embodiment, although it is assumed that the voltage of a commercial 
single-phase power source is 100 volts and the rated voltage of the 
three-phase motor 4 is 200 volts, if the voltage of a commercial power 
source is different from 100 volts, for instance in the case of 120 volts, 
the rated voltage of the three-phase motor 4 is then 240 volt which is 
twice the rated line voltage. The single-phase power source inverter 
system 6 has a structure as shown in the block diagram of FIG. 2. A 
single-phase 100 volt a.c. is input through terminals R and S to be 
converted into d.c. power of 200 volts by way of a voltage doubling and 
rectifying circuit 11. The d.c. power is smoothed by a smoothing capacitor 
12, and is converted into an a.c. power of 200 volts by an inverter 13 to 
output three-phase a.c. of 200 volts through terminals u, v and w. In the 
drawing, references C.sub.1 and C.sub.2 are smoothing capacitors for the 
voltage doubling and rectifying circuit 11, the references D.sub.1 and 
D.sub.2 are rectifier diodes, and the references D.sub.3 and D.sub.4 are 
flywheel diodes. The reference R2 is a current-detecting resistor; the 
reference IM is a three-phase induction motor whose rated voltage is 200 
volts. A control circuit power source 14; an overvoltage detecting circuit 
15; an undervoltage detecting circuit 16; an overcurrent detecting circuit 
17; a soft start setting circuit 18 is provided. A manually operable 
potentiometer 19 connected between a d.c. voltage +V and ground. An A/D 
converter 20, a display circuit 21; a base drive circuit 22; and an 
abnormal output signal circuit 25 are also provided. 
FIG. 3 shows waverforms of input and output voltages of the inverter 
system, and more specifically, it is illustrated how an input of 
single-phase 100 volts, 50 Hz is converted into an output of three-phase 
200 volts, 25 Hz. Conduction timings of transistors which are switching 
elements of the inverter 13 are controlled by the base drive circuit 22 to 
obtain an approximate sinusoidal wave shown in FIG. 3. The output voltage 
and frequency can be controlled as will be described later. 
The control circuit 25 receives respective detection signals from the 
overvoltage detecting circuit 15, undervoltage detecting circuit 16, 
overcurrent detecting circuit 17, a soft start setting signal from the 
soft start setting circuit 18, a speed setting signal from the A/D 
converter 20 to feed the base drive circuit 22 with a control signal 
through a given computation. This control circuit 25 comprises a 
general-purpose microprocessor (CPU), ROMs, RAMs, interfaces and so on. 
The control circuit power source 14 supplies the control circuit 25 with 
given d.c. power voltage, and as shown in FIG. 4 a d.c. voltage between 
both terminals (P-N terminals) of the capacitor 12 is input into a 
switching circuit 30 to form a pulse waveform, and then voltage regualtion 
is performed by a pulse transformer 31 to obtain a d.c. output of a given 
voltage by a rectifier 32. 
The overvoltage detecting circuit 15 whose block diagram is shown in FIG. 
5, compares a d.c. voltage between both terminals (P-N terminals) of the 
capacitor 12 with a reference value using a comparator 34, and is arranged 
to output an H or L level signal obtained through this comparison via a 
photocoupler 35. In FIG. 5, a filter 33 is a LPF for removing ripple 
components. 
Since the undervoltage detecting circuit 16 and the overcurrent detecting 
circuit 17 have substantially the same structure as the overvoltage 
detecting circuit 15, illustration of these circuits is omitted. 
The soft start setting circuit 18 whose structure is shown in FIG. 6 
comprises a dip switch 37 having four circuits, and four resistors 38-1 to 
38-4, and is arranged to send 4-bit data set in advance to the control 
circuit 25. The function of this soft start setting circuit 18 will be 
described in connection with a flowchart of a CPU which will be described 
later. 
The display circuit 21 comprises, for instance, a lamp and its drive 
circuit for informing a user of an abnormal state by repeatedly flashing 
the lamp on an abnormal state such as the increase of the load of the 
motor IM. 
The base drive circuit 22 is arranged to control the timing of turning on 
and turning off the power transistors in the inverter 13 on the basis of 
determined results, and the structure of this base drive circuit 22 may be 
the same as a general base drive circuit conventionally used. 
FIG. 7 is a flowchart showing the operational flow of the CPU which is a 
main element of the control circuit 25. As is clear from FIG. 7, when any 
one of the detection signals from the circuits 15 to 17 indicates an 
abnormal state, the display circuit 21 is driven to inform a user of an 
abnormal state by flashing the lamp or by other methods. 
When an abnormal state is not present, 4-bit data from the soft start 
setting circuit 18 input is, and an address of a ROM within the control 
circuit 25 is designated by this 4-bit data to read out corresponding data 
from the ROM. This data is used for determining frequency and voltage of 
the three-phase power to be fed to the motor IM, and is used for 
controlling the inverter 13 through the base drive circuit 22. 
A next step is for determining whether a predetermined period of time has 
lapsed or not after an unshown power switch is turned on. More 
specifically, a starting current flows for this predetermined period of 
time after the power switch is turned on, and therefore, the voltage (V) 
and the frequency (f) of the three-phase power to be applied to the motor 
IM are controlled on the basis of the data read out of the ROM. For this 
period, the control of the stating current is performed irrespective of a 
speed set by the manually operable potentiometer 19. 
FIG. 8 is a graph showing the relationship between the voltage (V) and 
frequency (f) of the output power from the inverter 13 on starting 
resulted from the soft start control. In this graph, five different curves 
are shown, and one of them is selected in advance by manipulating the dip 
switch 37 shown in FIG. 6. As shown in the drawing, it is possible to 
respectively change the frequency between several Hz and 120 Hz, and the 
voltage between 10 or more volt and a rated voltage. 
Turning back to the flowchart of FIG. 7, after the above mentioned 
predetermined period of time has lapsed, the base drive circuit 22 is 
controlled in the same manner as in conventional circuits to control the 
inverter 13 so as to obtain a motor rotational speed set by the 
potentiometer 19. 
From the foregoing detailed description of the invention, it will be 
understood that the the electric floor cleaner according to the present 
invention comprises a single-phase power source inverter system of 
single-phase 100 volt input and three-phase 200 volt output, a three-phase 
200 volt motor connected to an output side of the single-phase inverter 
system, where the motor is used for driving a floor cleaning member, such 
as a rotary brush, and soft start means, thereby proving the following 
advantages: 
(a) The electric floor cleaner can be manufactured at a low cost utilizing 
a standard motor and standard parts, such as an inverter. 
(b) It is possible to safely use the driving motor up to approximately 1.3 
kilowatt even if the above mentioned current limit of 20 A is present, and 
therefore, motor output can be increased. 
(c) The size of the cleaner can be reduced to the minimum when compared 
with the aforementioned systems A to F. 
(d) The efficiency and power factor are the best when compared with the 
aforementioned systems A to F, and therefore, the cleaner can contribute 
to improvement of power factor of transforming equipment or the like. 
(e) Electromagnetic vibrations which give undesirable influences to an 
operator can be drastically reduced. 
(f) The starting current can be reduced to the minimum when compared with 
the aforementioned systems A to F and the system disclosed the Japanese 
patent application provisional publication No. 61-249427. 
The above described embodiment is just an example of the invention and 
therefore, it will be understood for those skilled in the art that various 
modifications and variations may be made without departing from the sprit 
of the invention.