This invention relates to torque wrenches such as an impact wrench
and a hydraulic wrench.
In utilization of an impact wrench, it is necessary to detect the
striking state in order to accurately control the tightening torque or accurately
grasp the number of tightened nuts. Conventionally, the striking state is detected
by detecting the reverse rotation of the main shaft of an air motor using a sensor
mounted to this main shaft. However, since this method requires the sensor to
detect the forward and reverse rotations of the main shaft disposed within the
impact wrench, it has disadvantages in that the machine would be enlarged and its
cost would be increased.
For solving such problem, it can be considered to employ a system
which detects the admitted pressure and detects the striking state as the impact
wrench being activated when the admitted pressure falls below a reference level.
With the use of this system, however, it is not possible to discriminate whether
the impact wrench is in the free-running (no-load rotating) state or striking state.
This is because the difference between the pressures generated in free-running
state and striking state is smaller than a variation in pressure which is inevitably
caused in the pressure source, thus making it impossible to distinguish one state
from the other.
FR-A-1 517 360 discloses a tightening control apparatus for a torque
wrench with the features included in the first part of claim 1. In Figure 2 of
that document, a fluid line including a restriction is connected in parallel to
a main valve inserted in the pressure supply line from a pressure source to the
wrench. When the actuating lever on the wrench is depressed, a change at the downstream
side of the restriction occurs and the thus produced pressure difference between
the upstream and downstream sides of the restriction is used to close a switch
which causes the main valve to be opened and pressure to be applied to the wrench,
and further causes an electrical timer to start. Upon lapse of the time interval
set by the timer, the main valve is closed. The known control apparatus again does
not distinguish between the free running state and the actual striking state of
US-A-3 590 582 describes another control apparatus for a torque wrench
in which the difference between the line pressure and the pressure occurring at
the input of the tool is detected in order to determine the start or the striking
condition of the tool. The known apparatus requires the line pressure to be maintained
at a substantially constant value.
In a further control apparatus disclosed in US-A-3,732,932, a predetermined
time interval, during which pressure fluid is applied to a wrench, is started when
the wrench is actually starting to do work to overcome an increased resistence.
The control apparatus of this document, however, requires more than one pressure
sensor, each associated with a pressure reservoir, and is therefore bulky and expensive.
It is an object of the invention to provide a tightening control
apparatus for a torque wrench which can accurately detect the striking state of
the wrench by means of a simple arrangement.
This object is met by the features included in claim 1.
During free-running, the admission pressure is kept at a specific
level and does not vary with time, so that the striking signal will not be produced.
In the striking state, however, a certain minimum degree of change occurs in the
admitted pressure for each striking and the striking signal is produced in accordance
with the change. An advantage of this is that, unlike the conventional system
of detecting the admitted pressure, the striking state is detected from a change
in pressure, thus ensuring the accurate detection of the striking state with a
In preferred embodiments, the number of produced striking signals
is counted (claim 3), or the time during which the striking signal is continuously
produced is measured (claim 4). According to either embodiment, when the count
value or the measured time reaches a set value, the admission of pressure is stopped,
thereby to ensure the accurate tightening torque control. By providing signal
output time altering means (claim 2), the detecting systems of these embodiments
may be switched from one to the other as needed. This further improves the accuracy
of the torque control.
According to another modification (claim 5), the tightening control
apparatus can measure the number of tightened nuts and can detect that this number
reaches a set number, thus ensuring an accurate management of tightened nuts numbers
in addition to an accurate torque control.
The foregoing objects, advantages and other features will become
more apparent from the detailed description of a preferred embodiment of this invention
with reference to the accompanying drawings in which:
- Fig. 1 is a diagram illustrating the general arrangement of a tightening control
apparatus for a torque wrench according to the preferred embodiment;
- Fig. 2 is a block diagram illustrating a control system of the apparatus; and
- Fig. 3 is a time chart illustrating operational states of the control system.
In Fig. 1 illustrating the general arrangement of the present apparatus,
reference numeral 1 denotes an admission source, reference numeral 2 an air hose,
and reference numeral 3 an impact wrench. The air hose 2 is provided with an electromagnetic
valve 4, a check valve 5 and a pressure transducer 6 in order from the side of
the admission source 1. The check valve 5 serves to prevent troubles originating
from reduction in pressure at the part of the admission source 1. Referring to
the same diagram, reference numeral 7 denotes a controller 7, which comprises
an input port 8 coupled to the pressure transducer 6, an output port 9 coupled
to the electromagnetic valve 4, a plurality of input ports 10 &peseta;&peseta;
which receive data with respect to a set number, and output ports 11 and. 12 which
respectively output a predetermined-number tightening end signal and an NG signal.
Fig. 2 is a functional block diagram of the controller 7. A pressure
signal from the pressure transducer 6 is input to a pressure signal amplifier 21
and is supplied therefrom to a pressure change detector 22 and a striking signal
output section 23. The striking signal output section 23 has a detection level
setting section 24, a signal output time altering section 25 and a reset level
setting section 26, and it outputs a striking signal. (The function of this section
23 will be described later.) The number of the striking signals output from the
section 23 is measured by a counter 27 and the time during which the striking
signal is continuously output is measured by a timer 28. When the measured values
reach values set in associated setting sections 29 and 30, a tightening end signal
is output. Based on the tightening end signal, an electromagnetic valve shutoff
section 31 closes the electromagnetic valve 4.
The controller 7 further comprises a number setting section 32 constituted
by digital switches and a counter section 33 which counts the tightening end signal.
When the count value reaches a value set in the section 32, a predetermined-number
tightening end signal is output from the counter section 33, thereby to stop a
sequence of a tightening operation. Reference numeral 34 denotes a remaining-number
indicator, which indicates how many nuts are left to be tightened by means of LEDS
(light-emitting diodes). The number setting section 32 may be one or more than
one in quantity. The controller 7 further has a timer section 35 which is reset
by a start signal produced at the time a sequence of a tightening operation starts.
When no predetermined-number tightening end signal is output within a predetermined
time after the timer section 35 is reset, an NG signal is produced. Reference numeral
36 denotes a timer adjusting section and reference numeral 37 a power source.
Referring to Fig. 3, the operation states of the above-described
controller 7 will be explained below. Referring to (a) in Fig. 3 illustrating the
output signal from the pressure transducer 6, the pressure change detector 22
extracts an AC component only from this output signal as a pressure change signal.
This pressure change signal has such a characteristic that it does not vary when
the impact wrench is stopped, has a large negative variation when the lever is
open, has a minute positive and negative variation when the impact wrench is in
free running state, and repeats a large positive variation and a small negative
variation for each striking (as can be seen in (b) of Fig. 3). In this connection,
when the negative variation caused upon opening of the lever reaches a reset level
set in the reset level setting section 26, the striking signal output section
23 resets the counter 27 or timer 28 and starts detecting the striking state.
A description will now be given with respect to the case where the
counter 27 counts the number of strikes. When a positive variation equal to or
greater than the detection level set in the detection level setting section 24,
i.e., when striking occurs, the striking signal output section 23 outputs the
striking signal for a predetermined time T&sub4; as shown in (c) of Fig. 3. Assume
now that this signal output time T&sub4;, which is set by the signal output time
altering section 25, is set shorter than a striking interval T&sub3;. The number
of the striking signals output is counted by the counter 27. When the count value
reaches the set value, the tightening end signal is output from the counter 27,
thereby to close the electromagnetic valve 4 followed by the closing of the lever
(see (d) and (e) of Fig 3). Upon the lapse of a predetermined time T&sub2; after
the electromagnetic valve 4 is closed, this valve 4 is automatically opened. When
the above tightening operation is repeated by a predetermined number of times and
the number of the tightening end signals counted by the counter section 33 reaches
the set value, the predetermined-number tightening end signal is output from the
section 33. This completes a tightening operation sequence.
A description will now be given with respect to the case where the
signal output time T&sub4; is set greater than the striking interval T&sub3; in
the signal output time altering section 25. In this case, the striking signal is
output as a continuous signal from the first striking. Thus, when the continuous
signal output time measured in the timer 28 reaches the set time T&sub1;, the tightening
end signal is output from the timer 28. The operation state thereafter is the
same as described in the previous case.
The foregoing description discusses the tightening control apparatus
for a torque wrench according to one embodiment of this invention. Needless to
say, the present apparatus is in no way restricted to this particular embodiment,
but may be modified in various manners within the scope of the appended claims.
For instance, some modification may be made in such a way that when the striking
interval T&sub3; is detected to be greater than a reference time, this event is
discriminated to be a disturbance, not an occurrence of striking, and countermeasure
can be taken by resetting the counter 27 or timer 28.