Steeping motor driving apparatus

A stepping motor driving apparatus includes a stepping motor and a pulse output circuit for outputting drive pulses for driving the stepping motor. A pulse generator generates further pulses which not only have frequency higher than that of the drive pulses but are capable of a variable duty factor at the frequency of the further pulses. A gate circuit receives the drive pulses from the pulse output circuit and the further pulses from the pulse generator so as to output the further pulses of the pulse generator during excitation of the drive pulses such that the stepping motor is driven by the further pulses outputted from the gate circuit.

BACKGROUND OF THE INVENTION 
The present invention relates to a stepping motor driving apparatus which 
is suitably applicable to, for example, a liquid infusion pump used in the 
medical field. 
Generally, a liquid infusion pump is used for feeding liquid under pressure 
from an upstream supply bag through a delivery tube to a downstream 
infusion cannula. The pump is driven by a stepping motor and a series of 
eccentric cams are mounted on a rotational shaft of the stepping motor. A 
finger is provided around a corresponding one of the eccentric cams so as 
to depress the delivery tube such that the liquid is fed under pressure. 
FIG. 1 shows an arrangement of such a known liquid infusion pump. The known 
liquid infusion pump includes a pump head 1, a four-phase stepping motor 2 
for driving the pump head 1 and a control unit 3 for outputting drive 
pulses to the stepping motor 2 and for controlling various portions of the 
known liquid infusion pump. Although not specifically shown, the pump head 
1 depresses a delivery tube provided between a supply bag and an infusion 
cannula so as to feed liquid under pressure. Meanwhile, the control unit 3 
is formed of a microcomputer. 
The known liquid infusion pump further includes a key input portion 4 
operable for adjusting the quantity of the liquid fed under pressure, 
etc., a display unit 5 for displaying pressure of the liquid, etc., an 
alarm indicator 6 for giving an alarm when pressure of the liquid is 
abnormal, etc. and a power source 7 for supplying electric power to the 
various portions of the known liquid infusion pump. 
FIGS. 2(a) to 2(d) show wave forms of drive pulses supplied from the 
control unit 3 to excitation coils of the phases of the stepping motor 2, 
respectively. The stepping motor 2 is rotated through sequential 
excitation of the excitation coils. 
In the known liquid infusion pump, a necessary quantity of the liquid is 
fed under pressure by maintaining the number of revolutions of the 
stepping motor 2 at a predetermined value. However, for example, in the 
case where torque of the stepping motor 2 is more than adequate for a 
given load owing to such factors as hardness of the delivery tube, drive 
current more than necessary is caused to flow through the stepping motor 
2, thereby resulting in large power consumption. 
SUMMARY OF THE INVENTION 
Accordingly, an essential object of the present invention is to provide, 
with a view to eliminating the above described drawbacks of the 
conventional stepping motor driving apparatuses, a stepping motor driving 
apparatus in which power consumption of a stepping motor is reduced while 
the number of revolutions of the stepping motor is maintained at a 
predetermined value. 
In order to accomplish this object of the present invention, a stepping 
motor driving apparatus according to the present invention includes a 
stepping motor and a pulse output circuit for outputting drive pulses for 
driving said stepping motor and comprises: a pulse generator for 
generating further pulses which not only have a frequency higher than that 
of the drive pulses but are capable of changing duty ratio at the 
frequency of the further pulses; and a gate circuit which receives the 
drive pulses from said pulse output circuit and the further pulses from 
said pulse generator so as to output the further pulses of said pulse 
generator during excitation of the drive pulses such that said stepping 
motor is driven by the further pulses outputted from said gate circuit. 
By the above described arrangement of the stepping motor driving apparatus 
of the present invention, the conventional drive pulses for driving the 
stepping motor and the further pulses which not only have the frequency 
higher than that of the drive pulses but are capable of changing duty 
ratio at the frequency of the further pulses are inputted to the gate 
circuit and the stepping motor is driven by the further pulses outputted 
from the gate circuit during excitation of the drive pulses. Therefore, 
since the coils of the stepping motor are not excited when the level of 
the further pulses stands at zero, power consumption of the stepping motor 
can be reduced. Accordingly, power consumption of the stepping motor can 
be lessened while the number of revolutions of the stepping motor is 
maintained at a value corresponding to the drive pulses.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, there is shown in FIG. 3, a stepping motor 
driving apparatus K according to one embodiment of the present invention. 
The apparatus K includes a pump head 1, a four-phase stepping motor 2 for 
driving the pump head 1 and a control unit 3 for outputting drive pulses 
for driving the stepping motor 2 and for controlling various portions of 
the apparatus K. Although not specifically shown, the pump head 1 is 
provided for depressing a delivery tube provided between a supply bag and 
an infusion cannula so as to feed liquid under pressure. The control unit 
3 includes a microcomputer. 
Furthermore, the apparatus K includes a key input portion 4 operable for 
adjusting quantity of the liquid fed under pressure, etc., a display unit 
5 for displaying pressure of the liquid, etc., an alarm indicator 6 for 
giving an alarm when pressure of the liquid is abnormal, etc. and a power 
source 7 for supplying electric power to the various portions of the 
apparatus K. The above described construction of the apparatus K is 
fundamentally the same as that of the prior art apparatus of FIG. 1. 
Moreover, in order to reduce drive current of the stepping motor 2, the 
apparatus K includes a pulse generator 8 and a gate circuit 9. The pulse 
generator 8 is provided for generating further pulses which not only have 
a frequency higher than that of the drive pulses but are capable of a 
variable duty factor at the frequency of the further pulses. Meanwhile, in 
response to the drive pulses from the control unit 3 and the further 
pulses from the pulse generator 8, the gate circuit 9 outputs the further 
pulses of the pulse generator 8 during excitation of the drive pulses such 
that the stepping motor 2 is driven by the further pulses outputted from 
the gate circuit 9. 
The gate circuit 9 is constituted by four AND gates 9a to 9d corresponding 
to respective excitation coils of the four phases of the stepping motor 2. 
The further pulses having a frequency higher than that of the drive pulses 
are, in common, supplied from the pulse generator 8 to one input terminal 
of each of the AND gates 9a to 9d. Meanwhile, the drive pulses are 
supplied from the control unit 3 to the other input terminal of each of 
the AND gates 9a to 9d. 
FIGS. 4(a) to 4(i) show wave forms of signals in the apparatus K. FIGS. 
4(a) to 4(d) show wave forms of the conventional drive pulses outputted 
from the control unit 3 acting as a pulse output circuit. FIG. 4(e) shows 
the further pulses outputted by the pulse generator 8, while FIGS. 4(f) to 
4(i) show the pulses outputted from the AND gates 9a to 9d of the gate 
circuit 9, respectively. In this embodiment, during excitation of the 
drive pulses shown rn FIGS. 4(a) to 4(d), namely while the drive pulses of 
FIGS. 4(a) to 4(d) are at high level, the further pulses of the pulse 
generator 8 are outputted from the AND gates 9a to 9d as shown in FIGS. 
4(f) to 4(i), respectively so as to drive the stepping motor 2. 
Accordingly, in this embodiment, the conventional excitatory duration is 
divided into repeated excitatory and nonexcitatory durations by the 
further pulses having the frequency higher than that of the drive pulses, 
thereby resulting in reduction of power consumption of the stepping motor. 
Namely, in the case where torque of the stepping motor is more than 
adequate for a given load, it becomes possible to reduce power consumption 
of the stepping motor while the number of revolutions of the stepping 
motor is maintained at a hitherto used value. 
Meanwhile, in this embodiment, in the case where torque of the stepping 
motor is not adequate for a given load, the key input portion 4 is 
operated so as to supply a control signal to the pulse generator 8 from 
the control unit 3 such that a high-level signal is outputted by the pulse 
generator 8 at all times. Thus, in this case, the stepping motor 2 is 
driven by the drive pulses from the control unit 3 in the same manner as 
the conventional stepping motor driving apparatus. 
In the above described embodiment, the further pulses outputted from the 
pulse generator 8 have a single frequency. However, it can also be so 
arranged that frequency of the further pulses outputted from the pulse 
generator 8 is controlled such that drive current of the stepping motor 2 
can be controlled more closely. 
As is clear from the foregoing description, in the stepping motor driving 
apparatus of the present invention, both the conventional drive pulses for 
driving the stepping motor and the further pulses which not only have the 
frequency higher than that of the drive pulses but are capable of 
available duty factor at the frequency of the further pulses are inputted 
to the gate circuit such that the stepping motor is driven by a 
combination of the pulses outputted from the gate circuit during 
excitation of the drive pulses. Accordingly, in accordance with the 
present invention, power consumption can be reduced while the number of 
revolutions of the stepping motor is maintained at the value corresponding 
to the drive pulses. 
Although the present invention has been fully described by way of example 
with reference to the accompanying drawings, it is to be noted here that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, unless otherwise such changes and modifications depart 
from the scope of the present invention, they should be construed as being 
included therein.