Electricity: motor control systems – Closed loop speed control system for dc motor with commutator – Armature control by digital or combined analog and digital...
Patent
1989-02-23
1991-09-10
Shoop, Jr., William M.
Electricity: motor control systems
Closed loop speed control system for dc motor with commutator
Armature control by digital or combined analog and digital...
388812, 388809, H02P 500
Patent
active
050481150
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to controlling devices for direct current electric motors. There are some known feeding devices for direct current motors that comprise means for measuring the rotational speed of the motor, such as dynamo-speedometers or encoders mechanically connected to the rotating organ whose speed of rotation one wants to measure. They are connected to a voltmeter indicator or to a recorder, on which the rotational speed is read; the said measuring means can furthermore be connected to one or more relays so as to obtain the stabilisation of the rotational speed of the motor, according to prefixed values.
These measuring means, however entail some disadvantages such as the presence of additional moments of inertia on the driving shaft, with consequent decrease in the maximum angular accelerations, increased weight and overall size of the motor, greater construction and maintenance costs of the motor.
Control devices for d.c. motors are known, employing the e.m.f. as a control parameter, as the motor speed is proportional to it. In particular, in ELECTRONIC DESIGN, Vol. 16 of 12.19.66, pages 100, 102, a method is disclosed, by which the e.m.f. is obtained from the well-known relationship:
The above-cited document, however, uses the so-calculated e.m.f., assuming that it is correct. This bears substantial drawbacks, as: not taken into account; this variation can instead be remarkable (having an order of 0.4%/.degree.C.); also considerably non linear, so rendering non linear also the variation of Ra.
A d.c. motor speed control device is also known from EP-A-55988, where is foreseen to feed the motor with current pulses, by measuring the e.m.f. during pulse intervals. The drawback associated with this device is that this method of operation disturbs the motor and, moreover, it does not take into account transients, that is the induced currents that flow in the motor while feeding is interrupted.
Aim of the present invention is therefore to obtain a d.c. motor speed control unit capable of overcoming the above-mentioned drawbacks, that is, a unit: operation, by taking into account the Ra variations according to correspondent temperature and time variations;
Such aim is attained by calculating the motor e.m.f. as the difference between the terminal voltage and the voltage drop at a reference resistor through which the armature current flows; then this value is used as a velocity feedback signal for the motor regulation. In particular, the terminal voltage is cyclically measured at two successive close instants during which the armature resistance and the motor e.m.f. can be considered constant; these terminal voltage values are stored, then elaborated to perform the actual armature resistance during that interval, then this value is multiplied for the instant current. The result is then subtracted from the terminal voltage and only at that time the resulting e.m.f. is used as a velocity feedback signal for the velocity feedback circuit.
The unit for carrying out such a proces comprises a resistance through which the armature current flows, a resistive divider for measuring the armature voltage, so that a feedback signal can be sent to the control circuit which also comprises a means for storing a reference speed, an adder for comparing this reference value with the feedback value, an amplifier for amplifying the difference between the two values which is used to operate the speed control unit. In particular, the velocity feedback signal is caused to pass through a logic unit before being sent to the control circuit. The logic unit is capable to store the values obtained at two successive close instants during which the armature resistance and the motor e.m.f. can be considered constant, in order to obtain the armature resistance by performing the two equations e.m.f.=V-RI and multiplying this value for the instance current, then subtracting the result from the terminal voltage. Then this corrected signal is sent to the speed control circuit.
According to a first embodiment of the present invent
REFERENCES:
patent: 2814768 (1957-11-01), Kinkel
patent: 3974428 (1974-04-01), Hafle
patent: 3999111 (1975-11-01), Bailey
patent: 4104570 (1976-10-01), Hamby et al.
patent: 4121142 (1977-07-01), Morser et al.
patent: 4177412 (1977-12-01), Minakuchi
patent: 4241299 (1980-12-01), Bertone
patent: 4449081 (1983-01-01), Doeman
patent: 4622500 (1985-07-01), Budelman
patent: 4768389 (1986-02-01), Nakakuki
"Simple Resistor Network Eliminated DC Tachometer", Electronic Design, No. 26, Dec. 19, 1968, By M. Kanner, pp. 100 and 102.
"Thyristorgespeiste Fordermachinen", BBC-Nachrichten, No. 4, 1976, By V. Mittenzwei et al., pp. 153-160.
GSE Di Venturino Gianfranco
Martin David
Shoop Jr. William M.
LandOfFree
Speed control unit for direct current electric motor with intrin does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Speed control unit for direct current electric motor with intrin, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Speed control unit for direct current electric motor with intrin will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-547002