Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a method of
sensing a position of a movable body and an apparatus
therefore and more particularly to improvements in a
method of sensing a position of a movable body by
directly or indirectly converting a unit movement of the
movable body into digital pulse signals and an apparatus
therefore suitable for sensing that a workups and a
tool have reached predetermined relative positions so as
to switch the control of approach means, particularly
for use in a machine tool, industrial machine or the like.
The present invention has been developed in
view of the hereinafter noted disadvantages of the prior
art and has as its first object the provision of a
method of sensing a position of a movable body and an
apparatus therefore wherein the position of the movable
body can be reliably sensed without using mechanical
limit switches being low in reliability or a complicated
servomechanism, the apparatus can be readily assembled
into a machine tool or the like, and moreover, the
manufacturing costs can be reduced.
The present invention has as its second object
the provision of a method of sensing a position of a
movable body and an apparatus therefore wherein the
position of the movable body can be reliably sensed
without using mechanical limit switches being low in
reliability or a complicated servomechanism, and position
sensing signals can be sustained for a predetermined
stroke.
According to an aspect of the present invention,
as herein broadly claimed, there is provided a method of
sensing a position of a movable body comprising the steps
of: defining a reference position at which said movable
body abuts against a stopper which stops said movable
body even if said movable body continues to be driven;
generating digital pulse signals related to incremental
movements of said movable body, said digital pulse
signals not being produced when said movable body abuts
against said stopper; counting said digital pulse
signals to produce an indication of the position of
said movable body; resetting said count when said
movable body abuts against said stopper irrespective of
the actual value of said count; and sensing the
coincidence of said count with a predetermined pulse
number corresponding to a predetermined position so as
to sense the fact that said movable body has reached
said predetermined position.
The position of the movable body can be sensed
in non-contact manner with a high degree of accuracy for
a long period of time without using mechanical limit
switches, a complicated servomechanism is not required,
the apparatus as a whole is rendered compact to reduce
the manufacturing costs, and the change of control
switching points from one to another is facilitated, so
that a multiple types of controls can be performed by one
and the same apparatus.
According to another aspect, the invention is
broadly claimed herein as a method of sensing a position of a
movable body by directly or indirectly converting a unit
movement of the movable body into digital pulse signals,
wherein said method includes: a first step of counting
the pulse signals; a second step of sensing the coincidence
of the number of the pulse signals counted in the first
step with a first predetermined pulse number corresponding
to a predetermined position preset and generating position
sensing signals in response to the above coincidence; and a
third step of sustaining the position sensing signals
emitted in the second step after the movable body leaves
the said predetermined position for the duration off
second predetermined pulse number corresponding to a
predetermined stroke the sustained position sensing
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I
signals indicating that the movable body has reached
the predetermined position and is within a predetermined
stroke from the predetermined position. The fact that the
movable body has reached the predetermined position and is
within the predetermined stroke from the predetermined
position can be reliably sensed without using mechanical
limit switches low in operating reliability, self
sustaining circuit, long dog or the like, and further
without using a complicated, expensive servomechanism.
Moreover, the change of the predetermined positions and
the change of the predetermined strokes can be performed
by rewriting of Random Access Memory (hereinafter referred
to as RAM) or the like of the limit detecting circuit,
thus rendering general purpose properties.
According to an additional aspect of the
invention, there is broadly claimed herein an apparatus
for sensing a position of a movable body for use in a
machine tool including: a slide base fixedly provided;
a slide table movable on the slide table in the forward and
backward directions; a DC motor for moving the slide table
forward or backward by rotating a feed shaft thread ably
coupled to a feed nut solidly secured to the slide table:
a DC motor driving circuit for controlling the rotational
direction and rotational speed of the DC motor; a speed
change setting circuit for supplying a proper approach
speed setting value in accordance with the forwarded
position of the slide table to the DC motor driving
circuit; a mechanical sequence circuit controlling the
DC motor driving circuit; a dead stopper solidly secured
to the inner wall surface of the slide base; a rotary
encoder for detecting a rotation of the feed shaft eon-
responding to a movement of the slide table; and a limit
detecting circuit for sensing an approach position of the
slide table in accordance with an output from the rotary
encoder and supplying same to a mechanical sequence circuit.
3~3~
Preferably, the rotary encoder includes a pair
of photoelectric elements spaced apart from each other
through 90~ in phase.
Preferably also the aforesaid limit detecting
circuit is made to include: an encoder input circuit for
receiving an output from the rotary encoder; an input
circuit for receiving a command during an output emitted
from the mechanical sequence circuit; an output circuit
for generating limit signals; an indicator circuit; a
peripheral interface capable of programming connected to
the encoder input circuit, the command input circuit, the
output circuit and the vindicator circuit; a central
operation processing unit; a Read Only Memory; a Random
Access Memory in which a predetermined pulse number is
written and stored; and a bus for interconnecting the
peripheral interface, the processing unit, the Read Only
Memory and the Random Access Memory.
A yet another aspect of the invention lies in
an apparatus for sensing a position of a movable body
on a base, comprising: a motor for moving said movable
body; a stopper for receiving and stopping said movable
body at a reference position; pulse generating means for
generating pulse signals in proportion to a distance of
movement of said movable body; counting means for counting
said pulse signals; reference position detecting means
for detecting that said pulse signals cease from being
generated for a predetermined period of time due to
stopping of said movable body by said stopper and
resetting said counting means in response thereto;
predetermined position presetting means for presetting
a number of said pulse signals corresponding to a pro-
determined position of said movable body; and comparing
means for detecting that said movable body reaches said
predetermined position when a value of said counting
means coincides with said number preset by said pie-
,
3C~
determined position presetting means.
Finally, another aspect of the invention is
broadly claimed herein as an apparatus for sensing a
position of a movable body on a base, comprising: a
motor for moving said movable body; pulse generating
means for generating pulse signals in proportion to a
distance of movement of said movable body; counting
means for counting said pulse signals; predetermined
positions presetting means for presetting a plurality of
numbers of said pulse signals corresponding to a plurality
of predetermined positions of said movable body; pro-
determined ranges presetting means for presetting a
plurality of numbers of said pulse signals corresponding
to predetermined ranges from said predetermined positions
preset by said predetermined positions presetting means;
and comparing means for detecting that said movable body
reaches each of said predetermined positions of said pro-
determined position presetting means when values of said
counting means coincide with said numbers preset by said
predetermined position presetting means and for detecting
that said movable body is in said ranges preset by said
predetermined ranges presetting means until values of said
counting means coincide with said numbers preset by said
predetermined ranges presetting means.
The above-mentioned features and objects of the
invention of the present application will become more
apparent by reference to the following description taken in
conjunction with the accompanying drawings, wherein like
referenced numerals denote like elements, and in which:
Fig. 1 is a block diagram showing the arrange-
mint of one example of the approach control device of the
machine tool in which the conventional mechanical limit
switches are used;
Fig. 2 is a block diagram showing the arrange-
mint of one example of the servomechanism provided
3~3~
therein with the conventional position feedback system;
Fig. 3 is a block diagram showing the arrangement
of the feed control device adopting an embodiment of the
method for sensing positions of movable bodies according
to the present invention;
Fig. 4 is a chart showing output wave shapes of
the rotary encoder in the above-described embodiment;
Fig. 5 is a chart showing the feed rate control
conditions of the slide table in the above-described
embodiment;
Fig. 6 is a flow chart showing the action of
the limit detecting circuit in the above-described
embodiment; and
Fig. 7 is a flow chart showing the action of the
limit detecting circuit in a second embodiment.
Description of the Prior Art.
Since the approach speed of the tool and the
like are controlled in accordance with the positional
relationship between a workups and a tool, i.e., the
progress of working in tool machines and industrial
machines in general, it is very important to accurately
sense the position of the tool or -the like. Consequently,
heretofore, as shown in Fig. 1 for example, in a machine
tool including: a slide base 14 fixedly provided for
working a workups 12 fixed on a jig 10; a slide table
18 supporting spindles 16 and movable in the forward and
backward directions on the slide base 14; a DC motor 24
for moving the slide table 18 forward or backward by
rotating a feed shaft 22 thread ably coupled to a feed
nut 20 solidly secured to the undersurface of the slide
table 18; a DC motor driving circuit 26 for controlling
the rotational direction and the rotational speed of the
DC motor 24; a speed change setting circuit 28 for
supplying a setting value of an approach speed properly
suitable for the forwarded positions of the spindles 1
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,
to the DC motor driving circuit 26; and a mechanical
sequence circuit 30 for controlling the DC motor
driving circuit I the slide table 18 is provided at
predetermined positions on the side surface thereof with
dogs 32 and the slide base 14 is provided at predetermined
positions thereof with mechanical limit switches 34
adapted to be ON-OFF operated by the dogs 32, whereby
the limit switch 34 is ON-OFF operated by the dogs 32 to
sense the forwarded position of the slide table 18, i.e.,
the spindles 16, so that the DC lottery driving circuit 26
can be controlled through the mechanical sequence circuit
30, thereby enabling to control the approach of the slide
table 18. In the drawings, designated at 35 is a bearing,
36 a stopper solidly secured to the front end face of the
slide table 18, 37 a dead stopper solidly secured to the
inner wall surface of the slide base 14, Curl and ~R2
normal-opposite rotation switching contacts for switching
the rotational direction of the DC motor 24, and
LSl LS4 approach speed changing contacts for changing
the approach speed in accordance with the progress of
working.
This method has such characteristic features
that it is very simple to effect the method and it
suffices to provide the mechanical limit switches 34
and dogs 3?, both of which substantially correspond in
number to required signal outputs at positions where
controls are required to be switched. However, the
mechanical limit switches are low in mechanical strength
and not satisfactorily protected from the atmospheric
conditions at the sites of factory such as oil, water,
dust and the like, and hence, tend to malfunction due to
the presence of chips, dust, cooling water and the like,
thus lacking in reliability. Furthermore, the positional
relationship between the limit switches and the dogs
tends to go out of order with age and it is difficult to
33~3
adjust the dogs. Further, there is little disadvantage
in the use off single purpose machine in which a single
workups is worked on by use of a single spindle.
However, in the use of a general purpose machine having
been demanded in recent years in which a plurality of
workings are effected on a single workups or a plurality
of work pieces, there is presented such a disadvantage that
the positions of the dogs and limit switches should be
changed each time the work pieces or spindles are replaced
with new ones, thus lacking in general-purpose properties.
With the machine tools as described above, in the
case position sensing signals emitted from the limit
switches are directly used in controlling the approach
means or the like, the position sensing signal should be
emitted not only at the instant the slide table reaches
the setting position but also should be emitted when the
slide table has reached the setting position and stays
within a predetermined stroke from the setting position,
the stroke being suitable for controlling the approach.
Consequently in the case point dog is used for switching
the limit switch 34 ON for a very limited predetermined
period of time for example, heretofore, a self-sustaining
circuit has been additionally used so as to sustain the
position sensing signals emitted from the limit switches
for a predetermined period of time corresponding to a
predetermined stroke, or another point dog has been
provided at a terminal point of the predetermined stroke
so as to ON-OFF operate a single limit switch by use of
two point dogs. As a result the relay sequence has
become complicated, reliability has been lowered, and
moreover, the costs for manufacture have been increased.
On the other hand, in the case a long dog is used which
can operate the limit switch 34 for a comparatively long
predetermined stroke, there are encountered such disk
advantages that: not only the long dog is decreased in
go
rigidity but also it is difficult to adjust the long dog, and the change in signal sustaining time requires
the long dog to be replaced. The above-described
disadvantages are true of the case a proximity switch is
used in place of the limit switch.
On the other hand, with numerically controlled
machine tools and the like which have recently been
manufactured, digital servomechanisms each provided
therein with a positional feedback system have been
adopted in many cases As shown in Fig. 2, this digital
servomechanism includes: a pulse generator 40 for
directly or indirectly transducing a movement of a
movable body I such as a slide table into a digital
pulse signal; a reversible counter 42 for reversibly
counting pulse signals emitted from the pulse generator
40 corresponding to the position of the movable body 38
and supplying a deviation between preset command signal
pulses and the pulse signals thus reversibly counted;
a D/A converter 44 for converting an output from the
reversible counter 42 into an analog signal; and a servo-
amplifier 46 for amplifying an output from the D/A
converter 44 and supplying an output to a servo motor 48
for controlling the position of the movable body 38.
The digital servomechanism as described above can monitor
the position of the movable body 38 from time to time,
and hence, it should lead to that the approach control
with a high degree of accuracy can be effected in the
ideal condition. However, in actual practice, in the
above-described servo-mechanism, the parts are large in
number, the construction is complicated, the manufacturing
costs are very high, the components are low in
reliability and backlash and the like in transmission
system contribute to unstable operation of the servo-
mechanism. Further, there is presented such a disk
advantage that a considerable scale of reconstruction
31~3
is required before the servomechanism having the
positional feedback system can be fitted to the convent
tonal machine tool.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
_ . _
Detailed description will hereunder be given
of embodiments of the present invention with reference
to the drawings.
A first embodiment of the present invention is
applied to the conventional machine tool shown in Fig. 1.
As shown in Fig. 3, the first embodiment includes: a
rotary encoder 50 for detecting a rotation of a feed
shaft 22 corresponding to a movement of a slide table 18
from a gear coupling I and a limit detecting circuit 52
for detecting an approach position of the slide table 18
in accordance with an output from the rotary encoder 50
and supplying an output to a mechanical sequence circuit
30; in place of dogs and limit switches. Other respects
are similar to those of the conventional example as shown
in Fig. 1, so that detailed description thereof will be
omitted.
For example, the rotary encoder 50 includes a
pair of photoelectric elements provided about a gear of a
gear coupling of the DC motor I being spaced apart from
each other through 90 in phase, and adapted to supply two
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different in phase depending on the rotational direction of the feed shaft 22, i.e.,
the approach direction of the slide table 18 as shown in Fig. 4 to the limit detecting
circuit 52.
The limit detecting circuit 52 includes: an encoder input circuit 54
for receiving an output from the rotary encoder 50; an input circuit 56 for receiving
a command during an output emitted from the mechanical sequence circuit 30;
an output circuit 58; an indicator circuit 60; a peripheral inter fence (hereinafter
referred to as "PI") 62; a central operation processing unit (hereinafter referred
to as "CPU") 64; a Read Only Memory (hereinaf ton referred to as EON 66; a
RAM 68; and a bus for connecting the above described components to one another.
In RAM 68 of this limit detecting circuit 52, first preset pulse numbers Pi P I,
corresponding to control change positions Pi Pi are written in and stored by
a program module separately prepared.
Description will hereunder be given of action with reference to Figs.
5 and 6. A DC motor 24 rotates a feed shaft 22 through a gear coupling 49 to
move a slide table 18 secured thereto with a feed nut 20 forward or backward
The slide table 18 is caused to rapid-approach to Pi Pi in response to limit
signals LSI LS4 obtained from the limit detecting circuit 52, to first-slow-approach
to Pi Pi, to second-slow-approach to Pi P 4 and finally, to rapid-return
to P" P, as shown in Fig. 5 for example. These approach speeds are preset
in a speed change setting circuit 28, and one of these speeds is selected by opening
or closing of a relay in the mechanical sequence circuit 30.
When the feed shaft 22 is rotated by the DC motor 24, the rotary encoder
50, being connected to the gear coupling 49, supplies two output pulses different
in phase from each other according to the rotating direction, normal or reverse,
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as shown in Fig. 4, and received by the encoder input circuit 54 of the limit detecting
circuit 52.
As shown in Fig. 6, the limit detecting circuit 52 receives command
signals during its operation from the mechanical sequence circuit 30 through the
input circuit 56, and is at rest during its non-operation. In the case the mechanical
sequence circuit 30 is supplying output signals, the two pulse signals being different
In phase through 90 from each other which are emitted from the rotary encoder
50 are discriminated whether they are in the forward direction (the normal rotation
of the encoder) or in the backward direction the reverse rotation owe the encoder).
In the case the encoder rotates in the normal direction and the slide table 18 moves
in the forward direction, abnormal output is to be described hereinaf ton from the
limit detecting circuit 52 are cleared and the pulse signals from the rotary encoder
50 are summed. While, in the case the encoder supplies the reversed signals and
the slide table 18 moves in the backward direction, the number of output pulses
supplied from the encoder in accordance with the rearward movement of the slide
table 18 is subtracted from the total sum of the pulse signals counted till then.
These summed or subtracted result is compared by CPU 64 with the first preset
pulse numbers p 1 P 4 corresponding to the predetermined positions Pi I, Pi .
When the former and the latter coincide with each other, ON-OFF condition of
the limit signals LO LS,I is changed and an output is supplied to the output
circuit 58 through PI 62. By this, the mechanical sequence circuit 30 can be
controlled in accordance with the position of the slide table 18. When the working
on and a stopper 36 at one side of the slide table 12 reaches an original position
where it comes into abutting contact with a dead stopper 37 secured to the end
face of a slide base 14, the forward movement of the slide table 18 becomes impost
I
sidle irrespective of what -the rotating torque is, so that no output pulses can be
obtained from the rotary encoder 50. Consequently, the condition of the outputs
from the rotary encoder 50 disappearing for a certain period of time is determined
to be the original position and the counter is reset. At this times before resetting,
it is discriminated whether the counted value of the counter at the lime of rupturing
to the original point comes to be about the first preset pulse number corresponding
Jo the original position (for example zero) or not. More specifically, when the
counted value of the counter is above the lower limit of the discrimination value
and below the upper linlit of the discrimination value, it is discriminated to be
a normal operation, the counted value of the counter is reset at the first preset
pulse number corresponding to the original position, rapid return is performed
and the succeeding working is started. On the other hand, when the counted value
of the counter is less than the lower limit of the discrimination value or over the
upper limit of the discrimination value, it is determined that the counted value
of the counter is shifted from the actual position of the slide table 18 due to an
abnormality in the mechanical or electrical system. Then, an abnormality is indicated
by the indicator circuit 60, and an abnormal output is supplied to the mechanical
sequence circuit 30 to stop the working.
Additionally, change of the limit signal (the control change signal point)
can be readily effected by correcting the data (corresponding to the distance from
the original point) of RAM 68 in the limit detecting circuit 52 by a program module
separately prepared.
A second embodiment of the present invention will now be described.
In this second embodiment, in RAM 68 in the limit detecting circuit 52, there
are written and stored not only first preset pulse numbers Pi Pi corresponding
3$~3~
to control change positions Pi Pi but also second preset pulse numbers t I to
corresponding to predetermined numbers of stroke T I To for holding limit signals
LO I LO" which are position detecting signals corresponding to respective control
change positions P I P Lo when the slide table lo reaches the respective control
change positions Pi P-, as in the aforesaid first embodiment. Other respects
are similar to those of the first embodiment, so that detailed description thereof
will be omitted.
In this second embodiment, limit signals from the limit detecting circuit
52 are supplied according to a flow chart shown in Fig. 7. More specifically, the
counted number pi output pulses supplied from the rotary encoder 50 to CPU 64
through the encoder input circuit 54 and PI 62 becomes a preset pulse number
P l corresponding to a predetermined position Pi preset, the limit signal LO 1 is
turned ON arid this ON condition is held for the duration of a predetermined pulse
number t l corresponding to a predetermined stroke T preset in RAM 68. Cons-
quaintly a DC motor driving circuit 26 is controlled by a predetermined stroke
To in response to this limit signal LO l through the mechanical sequence circuit
30. In the case, the counted number pi counted by CPU 6~1 coincides with a preset
pulse number Pi corresponding to a predetermined position Pi preset, the limit
signal LO 2 is turned ON, and this ON condition is held for the duration of a prude-
termined pulse number t 2 corresponding to a predetermined stroke t 3 . Likewise,
in the case the counted number pi coincides with a preset pulse number pi, the
limit signal LO 4 is sustained for the duration of a predetermined pulse number
t " . The mechanical sequence circuit 30 is controlled by these limit signals in
accordance with the position of the slide -table 18. Other respects are similar
to those of the first embodiment, so that detailed description thereof will be omitted.
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Jo
In each of the above described embodiments, such an instant is not
discriminated as the original point that the stopper 36 on the side of the slide
table 18 comes into abutting contact with the dead stopper 37, but such a point
is discriminated as the original point that the stopper 36 is continuously pressed
against the dead stopper 37 for a predetermined period of time under a substantially
constant force by the torque of the DC motor 24. Hence, errors due to a backlash,
return and the like can be minimized. Additionally, in each of the above described
embodiments, the reference position is selected to be tile position of work being
completed at the forward-most position of the slide table. however, the reference
position should not be limited to this but the reference portion may be selected
to be the position of return being completed at the rearward-most position of
the slide table. Furthermore, in each of the above described embodiments, the
reference pro itchiness are selected to be travel-ending positions (i.e., stroke ends)
of the slide table 18, however, the reference position should not be limited to
these positions, by t the reference post lions may be selected to be intermediate
positions or intermediate working positions where certain working are completed.
Furthermore, in each of the above described embodiments, two pulse
signals having a difference in phase through 90 are adapted to be supplied from
the rotor encoder 50, the types of the output signals from the rotary encoder
should not be limited to the above, but, in the case a row of single pulses are used
as the output signals from the rotary encoder, the mechanical sequence circuit
30 May supply forward and backward commands for discrimination of rotating
direction, or the rotary encoder itself may generate pulse signals different from
each other in the case of normal or reverse rotation. In this case, the operation
of the limit detecting circuit may be more simplified.
- 14 _
I
Furthermore, in each of the above described embodiments, the limit
signals are incorporated in the mechanical sequence circuit consisting of the relay
sequence circuit, but, needless to say, the limit signals may be incorporated in
a sequencer which has been widely used in recent years.
Further, in each of the above described embodiments, the present invent
lion is applied to a machine tool, in which a slide table is corltrolled in its approach
by a DC motor, the scope of applications of the present invention should not be
limited to this, but may be likewise applied to generally used machine tools i
which the slide table is controlled in its approach by a hydraulic or pneumatic
cylinder and the approach speed is changed by switching the flow rate of hydraulic
oil or air.
From the foregoing description, it should be apparent to one skilled
in the art that the above described embodiment is but one of many possible specific
embodiments which can represent the applications of the principles of the present
invention. Numerous anti varied other arrangements can be readily devised by
those skilled in the art without departing from the spirit and scope of the invention.
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