1. * GB780110 (A)
Description: GB780110 (A) ? 1957-07-31
Improvements in or relating to electrical control systems for machine tools
Description of GB780110 (A)
PATENT SPECIFICATION
Date of Application and filing Complete Specification: Aug. II, 1955.
780,110 No. 23202/55.
Application made in Germany on Aug. 11, 1954.
Complete Specification Published: July 31, 1957.
Index at acceptance:-Class 38(4), A213B2 International
Classification:-H02j.
COMPLETE SPECIFICATION
Improvements in or relating to Electrical Control Systems for Machine
Tools I, CARL KRUG, of German Nationality, of 4, Cretzschmarstrasse,
Frankfurt a. Main, Germany, do hereby declare the invention for which
I pray that a patent may be 6 granted to me, and the method by which
it is to be performed, to be particularly described in and by the
following statement:This invention relates to electrical control
systems for machine tools.
According to the present invention there is provided an electrical
control system for a machine tool, employing a feeler for contacting
the surface of a workpiece, wherein the feeler is associated with
electrical contacts which require a relatively low loading current,
and is arranged to control the operation of a cold-cathode relay valve
the latter being connected to operate a low-current relay and wherein
the lowcurrent relay is arranged to control a switching relay for the
feed-motor of the tool, said switching relay being arranged to be held
in the "ON" position by means of a further circuit which is
independent of the valve, the arrangement being such that whilst the
switching relay is held "ON" the apparatus associated with the circuit
of the valve is switched off.
For a better understanding of the invention and to show how the same
may be carried into effect reference will now be made to the
2. accompanying drawing which illustrates a control circuit for a
grinding machine.
A feeler 1 raised by an oversized part on a workpiece 2 opens a
contact 3 and thus causes a cold-cathode relay valve 4 to strike.
A low-current relay 5, which is connected in the anode circuit of the
valve 4, is actuated by the anode current, and operates a switching
relay 7 through a contact 6. By using a low current relay it is
possible always to ensure that the valve 4 is [Price 3 / 6] lightly
loaded.
The switching relay 7 following the lowcurrent relay 5 is switched on
for a short period by the low-current relay but the "ON" state of the
switching relay is maintained through a second circuit 8 by means of a
self-maintaining contact 9 operated by the switching relay 7.
When the switching relay 7 is switched "ON," break contacts 10 thereof
simultancously switch off all the circuit elements associated with the
circuit of the valve 4.
The feed movement of a grinding head relative to the workpiece is
simultaneously initiated by known means. Extinction of 60 the valve
circuit causes the feeler contacts 3 to be electrically isolated until
the switching relay is opened.
Opening of the relay 7 can be effected, for instance, at the reversal
points of longtable machines and by table contacts 11 in the case of
circular table machines.
It will be seen from the figure that the contacts 11 make or break the
energising circuit of the switching relay. 70 Switching-off can,
however, also be effected through the agency of a time relay.
The relay valve ensures high sensitivity and therefore great switching
precision of 75 the feeler.
The feeler contacts are very light loaded, and no arcs are produced
which might vary contact properties, so that the reference value
initially set remains constant. 80 The low-current relay in the anode
circuit of the relay valve 4 only needs a fraetion of the maximum
anode current for energisation. Such fraction may be drawn from the
valve 4 for a period which is 85 adequate to ensure the operation of
the relay 7. The use of a low-current relay in combination with a
switching relay enables the frequency of switching to be increased as
compared with frequency of switching 90 780,110 obtainable with the
use of a combination comprising a condenser, relay valv-e and
switching relay. This is because the omission of the condenser
eliminates the time period which is required for charging a condenser.
Closure of the relay 7 extinguishes the relay valve so that the same
is not used for long periods.
If desired the circuitry can be arranged so that only a number of
relay pulses or long actuations of the electrical contacts associated
3. with the feeler will initiate a switching sequence.
The partial loading and short "ON" period increase operational life
considerably and assist in maintaining the striking point stable.
The switching relay following the lowcurrent relay obtains holding
current from another circuit and does not load the valve circuit. The
relatively considerable output power which the switch relay provides
for control purposes can therefore be delivered for as long as
required as is necessary, for instance, in grinding.
The combination of a cold-cathode relay valve with a low-current relay
and switching relay in this circuit arrangement makes it possible to
provide an automatic grinding operation or the like with simple and
cheap means, a high degree of reliability and a long operational life
being ensured.
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![accompanying drawing which illustrates a control circuit for a
grinding machine.
A feeler 1 raised by an oversized part on a workpiece 2 opens a
contact 3 and thus causes a cold-cathode relay valve 4 to strike.
A low-current relay 5, which is connected in the anode circuit of the
valve 4, is actuated by the anode current, and operates a switching
relay 7 through a contact 6. By using a low current relay it is
possible always to ensure that the valve 4 is [Price 3 / 6] lightly
loaded.
The switching relay 7 following the lowcurrent relay 5 is switched on
for a short period by the low-current relay but the "ON" state of the
switching relay is maintained through a second circuit 8 by means of a
self-maintaining contact 9 operated by the switching relay 7.
When the switching relay 7 is switched "ON," break contacts 10 thereof
simultancously switch off all the circuit elements associated with the
circuit of the valve 4.
The feed movement of a grinding head relative to the workpiece is
simultaneously initiated by known means. Extinction of 60 the valve
circuit causes the feeler contacts 3 to be electrically isolated until
the switching relay is opened.
Opening of the relay 7 can be effected, for instance, at the reversal
points of longtable machines and by table contacts 11 in the case of
circular table machines.
It will be seen from the figure that the contacts 11 make or break the
energising circuit of the switching relay. 70 Switching-off can,
however, also be effected through the agency of a time relay.
The relay valve ensures high sensitivity and therefore great switching
precision of 75 the feeler.
The feeler contacts are very light loaded, and no arcs are produced
which might vary contact properties, so that the reference value
initially set remains constant. 80 The low-current relay in the anode
circuit of the relay valve 4 only needs a fraetion of the maximum
anode current for energisation. Such fraction may be drawn from the
valve 4 for a period which is 85 adequate to ensure the operation of
the relay 7. The use of a low-current relay in combination with a
switching relay enables the frequency of switching to be increased as
compared with frequency of switching 90 780,110 obtainable with the
use of a combination comprising a condenser, relay valv-e and
switching relay. This is because the omission of the condenser
eliminates the time period which is required for charging a condenser.
Closure of the relay 7 extinguishes the relay valve so that the same
is not used for long periods.
If desired the circuitry can be arranged so that only a number of
relay pulses or long actuations of the electrical contacts associated](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)