Stepping motor driving apparatus

Abstract: A stepping motor driving apparatus (K) including a stepping motor (2) and a pulse output circuit (3) for outputting drive pulses for driving the stepping motor (2) and comprising: a pulse generator (8) 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 (9) which receives the drive pulses from the pulse output circuit (3) and the further pulses from the pulse generator so as to output 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).

Description: 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 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 show 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 constituted by a microcomputer. The known liquid infusion pump further 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 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 sufficiently large 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. In DE-A-3 302 209 a stepping motor driving apparatus is disclosed which divides each driving pulse in a chain of pulses of higher frequency and with variable duty ratio in order to reduce energy consumption. SUMMARY OF THE INVENTION Object of the invention is to provide another stepping motor driving apparatus generating a driving pulse form basically known from DE-A-3 302 209. 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 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. BRIEF DESCRIPTION OF THE DRAWINGS This object and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which: Fig. 1 is a block diagram of a prior art liquid infusion pump (already referred to); Figs. 2(a) to 2(d) are views showing wave forms of drive pulses in the prior art liquid infusion pump of Fig. 1 (already referred to); Fig. 3 is a block diagram of a stepping motor driving apparatus according to one embodiment of the present invention; and Figs. 4(a) to 4(i) are views showing wave forms of signals in the stepping motor driving apparatus of Fig. 3. Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. 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 is constituted by 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 changing duty ratio 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 in 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 sufficiently large 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 sufficiently large 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 changing duty ratio 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 as defined by the claims, they should be construed as being included therein.

Claims: A stepping motor driving apparatus (K) including a stepping motor (2) and a pulse output circuit (3) for outputting drive pulses for driving said stepping motor (2), said stepping motor driving apparatus comprising: a pulse generator (8) 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; characterized by a gate circuit (9) which receives the drive pulses from said pulse output circuit (3) and the further pulses from said pulse generator so as to output the further pulses of said pulse generator (8) during excitation of the drive pulses such that said stepping motor (2) is driven by the further pulses outputted from said gate circuit (9). A stepping motor driving apparatus (K) as claimed in Claim 1, wherein said stepping motor (2) is a four-phase motor and said gate circuit (9) is constituted by four AND gates (9a-9d). A stepping motor driving apparatus (K) as claimed in Claim 1, wherein said pulse output circuit (3) is constituted by a microcomputer. A stepping motor driving apparatus (K) as claimed in Claim 2, wherein said pulse output circuit (3) is constituted by a microcomputer.

Inventors: BOWMAN GEORGE A, KAWAHARA MASAFUMI, MATTHEWS JOSEPH B, BOWMAN, GEORGE A., KAWAHARA, MASAFUMI, MATTHEWS, JOSEPH B.
Applicants: BAXTER INT, SHARP KK, BAXTER INTERNATIONAL INC., SHARP KABUSHIKI KAISHA
Application year: 1990
Main classification: H02P8
IPC codes: H02P8