Safety device

A safety device for an apparatus to be manipulated by an operator. The apparatus is connected via a supply line for a supply means to a supply means source. A handgrip is provided to be grasped by the operator for controlling the operation of the apparatus. An operating sensor is actuated by the operator and is connected to the control device. The operating sensor may be an electric proximity switch provided so that it is possible to shut off the apparatus when the operator ceases to actuate the operating sensor. The operating sensor, or at least one indicator element of the operating sensor, is disposed on the hand of the operator, particularly integrated into a protective glove for the hand of the operator.

FIELD OF THE INVENTION 
The invention relates to a safety device for an apparatus used by an 
operator, the apparatus to be used by an operator being connected to a 
power supply via a supply line, comprising a handgrip grasped or enfolded 
by the operator, where the operation of the apparatus is preferably 
controllable from the power source, with a control device for the control 
of the operation of the apparatus and with an operating sensor disposed on 
the apparatus, which is actuated by the operator and preferably connected 
with the control device via a cable, the operating sensor being designed 
as an electronic proximity sensor, preferably operable contact-free, which 
is preferably actuated by a special actuation element, particularly a 
foil, preferably aluminum, copper, a material of low magnetic retentivity 
with high initial permeability, such as Mumetal or the like, and where the 
apparatus can be switched off when the action on the operating sensor by 
the operator stops. 
BACKGROUND OF THE INVENTION 
A safety device of the type discussed is recommended for all types of 
apparatus used by an operator, in order to protect the operator against 
accidents or to avoid unsupervised operation of the apparatus used by the 
operator. A safety device of this type is recommended, for example, for a 
grinder, milling machine or the like, as well as for a water or foam type 
fire extinguisher of a fire fighting device, an acetylene torch, a spray 
head for paint work or metal die casting, etc. Such a safety device is of 
particular importance for a sandblasting device of a sandblasting unit for 
pressure sandblasting--dry blasting, moist blasting, wet blasting--where 
such a safety device acting, so to speak, as a deadman's switch is 
required by safety regulations. Without intending to limit of the filed of 
application of a safety device of the type discussed, this safety device 
is primarily explained below by means of the example of a sandblasting 
device. 
In a known safety device for an apparatus to be manipulated by an operator 
(DE-U No. 86 13 771), particularly intended and usable for a sandblasting 
device of a sandblasting unit, where the device to be manipulated by the 
operator is connected via a supply line for a supply means, in this case 
compressed air, to a supply source, the operation of the device is 
controlled from the supply source. A control device is provided on the 
supply means source, by means of which the input of the supply means can 
be controlled. The control device is actuated by an operating sensor 
disposed on a handgrip of the device. The operating sensor is connected 
via a cable to the control device. When the actuation of the operating 
sensor by the operator ceases, the device is switched off. 
The operating sensor of the known safety device is designed as an 
electronic proximity sensor, preferably operable contact-free, which is 
preferably actuated by a special actuation element, particularly a foil. 
Besides the operating sensor the device is further provided with a normal 
operating unit for remote operation of the device. This normal operating 
unit has a plurality of activating elements for differing functions. 
In the previously described known safety device there is furthermore 
provided a relief device for the supply line for the purpose of switching 
off the device as quickly as possible. This relief device is disposed at a 
point in the supply line distant from the device near the connection of 
the supply line to the supply means source. It has a relief cross section 
which approximately corresponds to the flow cross section of the supply 
line. A shut-off device for the supply line is associated with the relief 
device, the two devices being locked off from each other in terms of 
circuitry. 
In the known safety device it is considerably more difficult to bypass the 
operating sensor than, for example, the mechanical hand lever of a 
deadman's switch or the like. However, a bypass is not impossible. 
Finally, although in the known safety device the reverse relief of the 
supply line, which is important for reasons of safety, is beneficial in 
its effects, it entails great expenditures for construction and the 
prevention of wear, especially if highly abrasive sandblasting means are 
used in a supply line. 
SUMMARY OF THE INVENTION 
It is an object of the invention to improve the known safety device such 
that a bypass of the operating sensor becomes for all practical purposes 
impossible and that the supply line is optimally shut off upon sensor 
response. 
This object is attained in a safety device for an apparatus used by an 
operator according to the present invention in that the operating sensor 
or at least one indicator element of the operating sensor is disposed on 
the hand of the operator, in particular that it has been integrated into a 
protective glove for the hand of the operator. Because of the fact that 
the operating sensor is provided on the hand of the operator, bypassing of 
the safety device or of the operating sensor is totally impossible, since 
the device itself is only passive. Without the operting sensor associated 
with the hand of the operator, operation of the device is systematically 
impossible. 
Furthermore, the object described above is also attained from the viewpoint 
of safety by the characteristic that the supply line can be compressed at 
least in the area of the relief device and/or the shut-off device, and 
that the relief device and/or the shut-off device, or both, each have a 
movable compression element. The provision of the relief device and/or the 
shut-off device as compression elements is particularly simple and sturdy 
and results in an optimal adaptation to the technical requirements even 
and especially with the use of highly abrasive sandblasting means as 
supply means. 
There are many ways to design the safety device according to the invention 
in a practical manner and to improve it. This is illustrated by means of 
the drawings in connection with the ensuing description of a preferred 
exemplary embodiment of a sandblasting unit equipped with a safety device 
of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
It should be mentioned beforehand that, instead of the sandblasting unit 
for compressed air blasting shown in FIG. 1, other devices may be used, 
for example a foam-type fire extinguishing unit as previously mentioned in 
the present description. The sandblasting unit shown in FIG. 1 has a 
compressed air line 1 connected to a supply means source 3, in this case 
in the form of a usual sandblasting supply container. From a connector of 
the sandblasting supply container 3 a supply line 7 leads to a device 8 
which is manipulated by an operator 30. In the exemplary embodiment shown 
here the supply line 7 is a line for compressed air and blasting sand, and 
the apparatus 8 is a sand blaster or blast nozzle. 
The sandblasting unit shown in FIG. 1 is provided with a safety device 9 
for the apparatus 8 which is manipulated by the operator having a control 
device 10 for controlling the operation of the apparatus 8 as well as an 
operating sensor 12 provided on the apparatus 8 which is actuated by the 
operator and which is connected with the control device 10 via a cable 11. 
The apparatus 8 can be switched off when the action on the operating 
sensor 12 by the operator 30 stops. 
As shown in FIG. 1 in combination with FIG. 2, the operating sensor 12 is 
inconspicuously placed in the exemplary embodiment shown here. This is 
made possible by the operating sensor 12 being embodied as an electronic 
proximity sensor which preferably can be actuated contact-free. In general 
such a proximity sensor can be actuated inductively, capacitively, 
optically, thermically or acoustically, and this will be further explained 
below. Furthermore, reference is made to the voluminous technical 
literature in connection with electronic proximity switches, preferably 
those actuable in a contact-free manner. 
It is further suggested in FIG. 1 that beside the operating sensor 12 a 
normal actuating unit 15 for remote control of the apparatus 8 has been 
provided. Such a normal actuating unit 15 is used for the normal operation 
of the apparatus 8 while the operating sensor 12 is used more for 
emergency operation, particularly in connection with a deadman's switch. A 
normal actuation unit 15 can have normal operating elements, for example, 
for the functions of sandblasting means on/off, compressed air on/off, 
additives on/off, and so forth. FIG. 2 shows that such a normal actuating 
unit 15 can be disposed physically separate from the apparatus 8, on a 
belt worn by the operator 30. 
FIGS. 1 and 2 further show that the apparatus 8 has a handgrip 17, which is 
to be grasped or enfolded by the hand of the operator 30, and that an 
intercom 19 is provided here, in accordance with the preferred teachings. 
The normal actuating unit 15 on the belt of the operator 30 serves 
simultaneously as a local central control unit and includes the intercom 
19. 
Finally it is suggested in FIG. 1 that at a location of the supply line 7 
remote from the apparatus 8, namely at a place close to the connection of 
the supply line 7 with the supply means source 3, there is provided a 
relief device 21 for the supply line as well as, and also in accordance 
with the preferred teaching, a shut-off device 22 for the supply line 7. 
The relief device has a relief cross section which approximately 
corresponds to the flow cross section of the supply line 7, so that a 
quick and effective relief in the reverse direction can take place. In the 
concretely shown exemplary embodiment the supply line 7 can, for example, 
have a diameter of 42 mm, i.e. have a flow cross section of approximately 
1,330 mm.sup.2. The relief device 21 would then also have this diameter. 
In a supply line of 400 m length, relief only takes a few seconds, clearly 
less than 5 sec. At the same time it can be assured by means of the 
shut-off device 22, with the locking of the relief device 21 and the 
shut-off device 22 that is provided, that no further supply means will 
flow from the supply means source 3. 
In the exemplary embodiment of a sandblasting unit shown in FIGS. 1 and 2 
as an example of such a unit in general, the operating sensor 12, here 
more exactly an indicator element of the operating sensor 12, is disposed 
on the hand of the operator 30. In the preferred exemplary embodiment 
shown here the indicator element of the operating sensor 12 has been 
integrated into a protective glove 32 for the hand of the operator 30. In 
the exemplary embodiment particularly clearly shown in FIG. 2 the 
indicator element of the operating sensor 12 is an air coil 33 which has 
been integrated here into the palm of the protective glove 32. The air 
coil 33 is connected in the exemplary embodiment shown here with a central 
electronic device or electronic triggering device via a connecting cable 
34, which will be described in more detail below. Plug or button contacts 
are indicated in the area of the wrist of the protective glove 32. In the 
preferred exemplary embodiment here shown the air coil is distributed flat 
across the palm and up into the index finger and thumb of the protective 
glove 32. The main point is that it is particularly practical if the 
indicator element is disposed in the palm of the protective glove 32 at a 
point maximally free of movement, particularly between thumb and index 
finger. However, the indicator element does not have to have the wide 
expanse concretely shown in FIG. 2. This results in a further safety 
measure, namely that grasping the apparatus 8 with the bare hand does not 
result in actuating the operating sensor 12, and thus the operator 30 is 
forced to wear the protective glove 32 at work. This results in the 
advantage that bypassing the operating sensor 12 and nullifying the safety 
effect of the safety device 9 of the invention is extremely difficult for 
the average operator 30. Since the operating sensor 12 is associated with 
the protective glove 32, i.e. with the operator 30, bypassing the safety 
device 9 is impossible, simply because the apparatus 8 itself is only 
passive. If the operating sensor 12 and particularly its indicator element 
can only be activated by a special actuator element, then it is suggested 
to dispose the actuator element on the apparatus 8 in the present 
exemplary embodiment, and in particular to integrate it flat into the 
surface of the apparatus 8. This has only been sketched in in FIG. 2. A 
point in particular is that, for example, the foil forming the actuator 
can be wound or glued around a nozzle, a nozzle holder or the supply line 
7 itself. Another point is that the actuator element can be integrated, 
particularly by vulcanizing, into a rubber hose, for example, which is 
attached to the apparatus 8 at a suitable spot. It is especially 
recommended to integrate the actuator element into the handgrip 17, 
preferably of course into the gripping surface of the handgrip 17. 
Previously it has already been briefly discussed that the electronic and 
preferably contact-free operable proximity switch of the invention can be 
operated as operating sensor by inductive, capacitive, optical, thermal or 
like means by the operator. Besides the embodiment as an inductive 
proximity switch previously thoroughly discussed, a number of further 
embodiments are to be discussed which have not been shown in the drawings. 
First, it could be recommended to provide the operating sensor in the form 
of a capacitive proximity sensor. The hand of the operator could then, for 
example, cause the actuation of the response capacity of the capacitative 
proximity sensor. 
A further alternative is also to provide the operating sensor in the form 
of a magneto-elastically operating sensor. For example, the 
magneto-elastic effect of such a sensor could be utilized during the 
grasping of a handgrip and the change of the mechanical load on a 
protective glove of an operator connected therewith. 
Similarly to a magneto-elastically operating sensor, a sensor operating 
piezo-electrically could be provided. In this case the mechanical work 
would be translated into electric voltage. 
In accordance with another alternative, the operating sensor could be 
provided as a wire strain gauge sensor, particularly with a least one 
semiconductor wire strain gauge. Such wire strain gauge sensors can be 
cheaply and practically used, especially when using modern semiconductor 
technology. 
Of particular importance is a further teaching of the invention 
characterized by providing the operating sensor as a sound sensor, 
preferably a structure-borne sound sensor, particularly a structure-borne 
sound microphone. Because of the susceptibility to interference of a sound 
sensor reacting to sound transmitted through the air, a structure-borne 
sound sensor is provided here in a particularly preferred way. Often a 
microphone specially tuned to structure-borne sound and structure-borne 
sound measurement is used. Such sensors are known from the technical 
literature. The supply means exiting the apparatus, particularly the 
sandblasting material carried by air pressure in a sandblasting unit, 
generates high-frequency oscillations in the apparatus, particularly in 
the nozzle body of the sandblasting unit. Now if, for example, a 
structure-borne sound microphone has been integrated into a work glove of 
an operator and is connected to the control device, this structure-borne 
sound microphone registers the structure-borne sound in the nozzle body 
whenever, and only whenever, the work glove tightly surrounds the handgrip 
of the nozzle body. This technique makes it unnecessary to adapt the 
apparatus itself in any manner. 
The only possible way to circumvent the operating sensor described above, 
in particular a structure-borne sound sensor, is to impose on it the 
structure-borne sound frequencies occurring in the operation of the 
apparatus itself. In order to provide a special level of protection 
against outside influence here, it is recommended that the control device 
have at least one frequency filter associated with the sound sensor. A 
frequency filter in the control device can be embodied, for example, as 
either a low-pass, high-pass or band-pass filter. It is also possible to 
connect several frequency filters in parallel in order to selectively 
determine different frequencies normally occurring during operation of the 
apparatus. Specific frequencies can also be filtered out with such 
frequency filters (set-point sound). 
In the previously discussed safety installation and sound sensor, not only 
is there a determination whether the operator is actually actuating the 
operating sensor, but it is determined at the same time whether or not the 
apparatus is operating. Although this is advantageous, it means a special 
provision must be made during the start-up of the apparatus, when there is 
no sound or structure-borne sound yet. In this case it is recommended that 
the control device be provided with a bypassing switch and that it be 
possible to bypass while the apparatus to be manipulated by the operator 
is starting up, until the corresponding set-point sound occurs. It can be 
provided in the design of the circuit that the bypassing switch in the 
control device is automatically opened as soon as a set-point signal, 
indicating actuation by the operator and the operation of the apparatus, 
has been generated. 
It has not been shown in the drawings that a delay switch can be associated 
with the operating sensor if this is considered practical given the 
circumstances of use. Also not shown in the drawings is that the operating 
sensor, as already mentioned, can be provided in the form of a proximity 
sensor only actuated by a special actuator element, particularly a foil, 
preferably of aluminum, copper, a material of low magnetic retentivity 
with high initial permeability, such as Mumetal or the like. Mumetal or 
materials with high initial permeability as they are known, for example, 
for use in magnetic screens, are suitable to a particular degree, since in 
this way metals such as steel, aluminum, zinc, copper or the like cannot 
interfere with the operating sensor. Accidental interference can therefore 
be safely prevented. 
Finally, FIG. 2 shows that in the exemplary embodiment shown therein the 
electronic control associated with the indicator element of the operating 
sensor 12 can be integrated into the normal actuating unit 15. 
Furthermore, FIG. 2 also shows that the intercom 19 is connected via a 
cable 35 with the normal actuating unit 15. 
Special attention is required for the connection via a cable 11 of the 
control device 10 to the apparatus 8 or to the operator 30. The cable 11 
can be divided, one part carrying the current supply for the operator 30 
and the other part transmitting the signals. Of course, by use of the 
corresponding filter techniques, single cables 11 can also be used. A 
particular problems lies in protecting the cable 11 against damage. In 
this respect FIG. 2 in combination with FIG. 1 shows a particularly 
preferred exemplary embodiment in that in this case a a ventilating air 
line 36 has been provided between the supply means source 3, or pressure 
generator, and the operator 30 and the cable 11 for the connection of the 
control device 10 with the apparatus 8 is disposed on the inside of the 
ventilating air line 36. This integration of the cable 11 and the 
ventilating air line 36, required in any case for protecting the breathing 
of the operator 30, guarantees a particularly protected way to bring the 
cable 11 to the operator 30. If a ventilating air line 36 per se is not 
present, the cable 11 can, of course, be integrated with other lines 
present, for example the supply line 7 or, more practically with an 
auxiliary air line perhaps extending parallel to the supply line 7. As far 
as the following explanation of the integration into the ventilating air 
line 36 is concerned, this is also correspondingly true for the 
integration into other lines. 
In the exemplary embodiment explained above, naturally the ventilating air 
line 36 should have a cable connector 37 or cable lead-in in the vicinity 
of the control device 10 and in the vicinity of the apparatus 8, 
respectively. Such a cable connector 37 can be in the form of a plug-in 
connection in a plurality of different ways. If embodied as a cable duct 
or cable lead-in, a discrete connecting element is not necessary. However, 
sealing of the led-in or ducted cable 11 is then required. In general, the 
state of the art should be considered in respect to the construction of 
such connectors or lead-ins. 
FIG. 1 shows a particular layout, in that here the ventilating air line 36, 
or any other line, comprises separate line segments 39 which can be 
connected by means of connecting elements 38, the connecting elements 38 
at the same time serving as pneumatic connections of the line segments 39 
and as the electrical connection of individual cable segments of the cable 
11. FIG. 4 shows this schematically for two line segments 39. 
As far as the relief device 21 and the shut-off device 22 are concerned, 
FIG. 1 shows these only schematically as shut-off elements. Such shut-off 
elements are in the form of ball-cock valves, slide valves, or the like. 
However, FIGS. 3, 4 and 5a-5d show particularly preferred embodiments of a 
relief device 21 for the supply line 7, and of a shut-off device 22, which 
are particularly simple and sturdy. The exemplary embodiments shown here 
require that the supply line 7 is compressible, at leat in the area of the 
relief device 21 and/or the shut-off device 22. This is true for the 
supply line 7 itself as well as for a relief connector 50 brought through 
the relief device 21. It is important in all cases that the relief device 
21 and/or the shut-off device 22, or both, each have one movable 
compression element 51 for compressing the corresponding supply line 7 or 
the relief connector 50. In the preferred exemplary embodiment here shown, 
the compression element 51 can be moved by a pneumatic or hydraulic drive, 
particularly by a bellows cylinder 52. 
The preferred embodiment shown in FIG. 3 has a supply line 7 and a relief 
connector 50 extending side by side and parallel to each other. A 
compression element 51 is disposed between the supply line 7 and the 
relief connector 50 in a housing 53, surrounding the relief device 21, the 
shut-off device 22, the supply line 7 in this area, the relief connector 
50 in this area and the compression element 51. By means of the propulsion 
by the bellows cylinder 52 shown here, which is actuable pneumatically, 
i.e. via a control pressure line 54, the compression element 51 of FIG. 3 
can either be moved downward for opening the supply line 7 and closing the 
relief connector 50, or upwards for relief, i.e. the opening of the relief 
connector 50 and the closing of the supply line 7. The drive thus works in 
two directions. This is attained in the preferred exemplary embodiment 
shown here by the provision, in opposition to the direction of action of 
the bellows cylinder 52, of a spring 55 embodied as a helical pressure 
spring, which normally tries to compress the bellows cylinder 52 and moves 
the compression element 51 in the device here shown in the direction of 
the state of relief. The supply line 7 is therefore open and the relief 
connector 50 closed only when the bellows cylinder 52 is under pressure, 
if the control pressure falls off, the spring 55 upwardly compresses the 
bellows cylinder of FIG. 3 and in this way compresses the supply line 7. 
FIG. 1 shows in connection with the above explanation that the control 
pressure line 54 for the relief device 21 and the shut-off device 22 can 
be readily connected to a common compressed air generator, with which, for 
example, the compressed air line 1 associated with the supply means source 
3 is also connected. For the purpose of controlling the bellows cylinder 
52, FIG. 3 additionally shows a control valve 56 on the control pressure 
line 54 which, in the exemplary embodiment shown here, can be provided as 
a simple 3/2-way valve. 
The further exemplary embodiment of the teachings previously explained in 
principle shown in FIGS. 4 and 5a-5d, first also has a compression element 
51 and a bellows cylinder 52 as a penumatic drive. This exemplary 
embodiment, described by means of FIG. 4 for the shut-off device 22 of the 
supply line 7 is distinguished by great simplicity and excellent 
retrofitting ability for existing supply lines 7. The housing 53 is here 
made in the shape of a box with lateral walls and front and back walls, 
the front and back walls each having approximately U-shaped recesses on 
their upper edges for receiving the supply line 7. The supply line 7 can 
be inserted from above into these recesses 57. As shown by FIG. 4, the 
housing 53 is then closed by a sliding lid 58 which in the inserted state 
is prevented by holding flanges on the housing 53 from upwardly lifting 
off the housing 53. With the compression element 51 on the bellows 
cylinder 52, which here is provided as a compression strip extending 
crosswise to the supply line 7, is associated a corresponding compression 
element 59 on the inside of the lid 58. If during operation and with the 
supply line 7 inserted compressed air is fed via the control pressure line 
54, also present here, to the bellows cylinder 52, the latter expands, 
lifts the compression element 51 upwardly and thus compresses the supply 
line 7 between the compression elements 51 and 59. Furthermore, a pressure 
relief line 60 for the bellows cylinder 52 is also shown. A control valve, 
not shown, for example a 4/2-way control valve, can be connected to the 
lines 54, 60. 
In a clearly comprehensible way the cooperation of a relief device 21 and a 
shut-off device 22, both constructed in accordance with the system of FIG. 
4, is shown in FIG. 5a-5d. The two bellows cylinders 52 which in the 
exemplary embodiment shown here constitute the drive for the compression 
elements 51, are connected to each other and to a control pressure line, 
not shown, via a control valve 56, here embodied as a 5/2-way valve, such 
that in case of a 1/0 signal, one of the two bellows cylinders 52 is 
always extended and the other of the two bellows cylinders 52 is always 
compressed. FIGS. 5a and 5c show the normal operating condition with the 
supply line 7 open and the relief connector 50 compressed, the direction 
of flow being shown in FIG. 5c. In FIGS. 5b and 5d the relief position is 
shown with the supply line 7 compressed and the relief connector 50 open, 
the directions of flow again in the lower right. This technology is 
especially practical and an existing system can be retrofitted easily. The 
design of the drives in the form of bellows cylinders 52 is sturdy and 
requires little maintenance, especially since the bellows cylinders 52 are 
protected against damage by the housing 53 in the present exemplary 
embodiment. The pneumatic control from the source of compressed air via 
the control pressure line is typical for the system and thus is 
particularly practical. 
It is to be understood that the description of the exemplary embodiments 
has been given by way of example only and that further improvements and 
variants are possible within the scope of the invention.