Fluid circuit for work handling apparatus

A fluid circuit for a work handling apparatus having a suction holder adapted to be selectively communicated with a vacuum source and a compressed air source, an having a first electromagnetic valve having first, second and third ports which are fluid-connected with the vacuum source, the compressed air source and the suction holder, respectively. The first electromagnetic valve is operable, when in a suction position, to communicate the first and third ports with each other and, when in a release position, to communicate said second and third ports with each other. The fluid circuit also has a first passage communicating the suction holder and the third port of the first electromagnetic valve with each other, a pressure sensor, a second electromagnetic valve operable to selectively establish and open a fluid circuit between the pressure sensor and the first passage. The fluid circuit is provided with a gas-liquid separating element disposed in the first passage for separating a liquid component, sucked into the suction holder and then into the first passage, from air. A parallel fluid circuit extends between the compressed air source and the second port of the first electromagnetic valve and including first and second flow regulators, and a switching valve is provided in the parallel fluid circuit for selectively connecting one or both of the first and second flow regulators into the parallel fluid circuit.

BACKGROUND OF THE INVENTION 
1. (Field of the Invention) 
The present invention generally relates to the handling of work in a 
grinding machine and, more particularly, to a fluid circuit for a work 
handling apparatus used in the work grinding machine for automatically 
picking up and releasing a work such as, for example, an optical lens 
element, onto and from a suction holder. 
2. (Description of the Prior Art) 
An example of work handling apparatus hitherto employed in an existing lens 
grinding machine is schematically shown in FIG. 3 of the accompanying 
drawings, reference to which will now be made for the detailed discussion 
thereof. 
The prior art work handling apparatus shown in FIG. 3 is of a type capable 
of handling a lens element to be polished and comprises a suction holder 2 
for releasably holding the lens element 1. This apparatus also comprises a 
source of vacuum employed in the form of a vacuum pump 3 pneumatically 
connected with the suction holder 2 through a tubing by way of an 
electromagnetic valve 4. The electromagnetic valve 4 has two operative 
positions, i.e., suction and release positions, and is operable to 
communicate the suction holder 2 with the vacuum pump 3 when in the 
suction position and with a source of compressed air 5 when in the release 
position. A portion of the tubing between the suction holder 2 and the 
electromagnetic valve 4 is pneumatically connected with a pressure sensor 
7 and a vacuum gauge 9. ON the other hand, the air supply tubing extending 
between the compressed air source 5 and the electromagnetic valve 4 has a 
flow controller 10 for regulting the flow of the compressed air from the 
compressed air source 5 towards the suction holder 2 through the 
electromagnetic valve 4. 
The prior art work handling apparatus of the above described construction 
operates in the following manner. Depending on the position of the 
electromagnetic valve 4, the lens element 1 can be selectively picked up 
by suction and released from the suction holder 2. When the lens element 1 
is picked up by the suction holder 2, the suction holder 2 is communicated 
with the vacuum pump 3 through the electromagnetic valve 4 then in the 
suction position, but when the lend element 1 is released from the suction 
holder 2, the latter is communicated with the compressed air source 5 
through the electromagnetic valve 4 then in the release position. The 
pressure sensor 7 is used to detect whether the lens element 1 has been 
picked up by the suction holder 2 or whether the lens element 1 is 
released from the suction holder 2. When it is desired to polish the lens 
element 1, the electromagnetic valve 4 is switched over to the release 
position after the lens element 1 picked up by the suction holder 2 has 
been pressed against a processing tool (not shown), and a grinding or 
polishing process is carried out for a predetermined length of time while 
an abrasive fluid is simultaneously supplied to the processing tool and 
the lens element. After the grinding or polishing process, the 
electromagnetic valve 4 is switched over to the suction position to cause 
the suction holder 2 to pick up the lens element thereby removing it from 
the processing tool. 
It has, however, been found that the prior art work handling aparatus has a 
problem in that, as the work handling apparatus is operated repeatedly 
through a number of cycles, the abrasive fluid tends to be sucked into the 
pneumatic tubing system and then into the vacuum pump, thereby causing 
damage to the vacuum pump. In addition, since the abrasive fluid once 
sucked into a portion of the pneumatic tubing when the electromagnetic 
valve has been in the suction position will enter the pressure sensor when 
the electromagnetic valve is switched over to the release position, the 
pressure sensor 4 may also be damaged. Those problems constitute a cause 
of reduction in reliability of the work handling apparatus. 
SUMMARY OF THE INVENTION 
The present invention has been made with a view to substantially eliminate 
the above discussed problems inherent in the prior art work handling 
apparatus used in operative association with a work grinding machine and 
is intended to provide an improved work handling apparatus having a high 
reliability and a minimized possibility of troubles and malfunctions. 
In order to accomplish the above described and other objects of the present 
invention, there is provided a fluid circuit for a work handling apparatus 
having a suction holder adapted to be selectively communicated with a 
source of vacuum and a source of compressed air. The fluid circuit 
comprises a first electromagnetic valve assembly having suction and 
release positions and also having first, second and third ports, which are 
fluid-connected with the vacuum source, the compressed air source and the 
suction holder, respectively. The first electromagnetic valve assembly is 
operable, when in the suction position, to communicate the first and third 
ports with each other and, when in the release position, to communicate 
said second and third ports with each other. The fluid circuit also 
comprises a first passage means communicating the suction holder and the 
third port of the first electromagnetic valve assembly with each other, a 
pressure sensor, a second electromagnetic valve assembly operable to 
selectively establish and open a fluid circuit between the pressure sensor 
and the first passage means. 
In accordance with the present invention, the fluid circuit for the work 
handling apparatus is provided with a gas-liquid separating element 
disposed in the first passage means for separating a liquid component, 
sucked into the suction holder and then into the first passage means, from 
air; parallel fluid passages extending between the compressed air source 
and the second port of the first electromagnetic valve assembly and 
including first and second flow regulators; and a switching valve means 
provided in the parallel fluid passages for selectively bringing one or 
both of the first and second flow regulators into communication with the 
second port of the first valve assembly. 
According to the present invention, only when it is necessary to determine 
if the work has been properly picked up by the suction holder is the 
second electromagnetic valve assembly activated to establish the fluid 
circuit between the pressure sensor and the first passage means thereby to 
avoid an undesirable ingress of the abrasive fluid into the first passage 
means. However, since there is a time lag between the time at which the 
first electromagnetic valve assembly is brought into the suction position 
and the time at which the second electromagnetic valve assembly is 
activated to establish such fluid circuit, the filter is used to separate 
the abrasive fluid from air entering into the first passage means through 
the suction holder during this time lag. 
Thus, it is clear that, according to the present invention, any possible 
damage to and/or malfunctioning of the work handling apparatus which would 
result from the ingress of the abrasive fluid can be advantageously 
avoided.

DETAILED DESCRIPTION OF THE EMBODIMENT 
Before the description of the present invention proceeds, it is to be noted 
that like parts are designated by like reference numerals throughout the 
accompanying drawings. 
Referring first to FIG. 1, the illustrated pneumatic circuit for the work 
handling apparatus according to the present invention comprises an 
electromagnetic valve 4 having suction and release positions. This 
electromagnetic valve 4 is operable, when in the suction position as 
shown, to communicate the suction holder 2 with the vacuum pump 3 through 
a pneumatic passage P1 and then through a pneumatic passage P2, but when 
in the release position, to communicate the suction holder 2 with the 
compressed air source 5 through the pneumatic passage P1 and then through 
a system as will be described later. The pressure sensor 7 and the vacuum 
gauge 9 are fluid connected with the pneumatic passage P1 through a 
sensing passage P3 having an electromagnetic valve 8 disposed therein. The 
electromagnetic valve 8 has two operative positions, i.e., open and closed 
positions, and establishes a communication between both the pressure 
sensor 7 and the vacuum gauge 9 and the pneumatic passage P1 when and so 
long as it is in the open position. 
The system between the pneumatic valve 4 and the compressed air source 5 
includes two pneumatic passages P4 and P5. The pneumatic passage P4 has a 
flow regulator 10 disposed therein for the control of the flow of the 
compressed air therethrough while the pneumatic passage P5 parallel to the 
pneumatic passage P4 has a flow regulator 11 for the control of the flow 
of the compressed air therethrough and an electromagnetic valve 12 both 
disposed therein, said electromagnetic valve 12 having two operative 
positions, i.e., open and closed positions. 
A portion of each of the pneumatic passage P1 between the suction holder 2 
and either of the electromagnetic valves 4 and 5 and the pneumatic passage 
P2 have air filters 13 and 14 disposed therein, respectively, each of said 
air filters being operable to lower the velocity of flow of air thereby to 
separate the abrasive fluid from the air. 
The work handling apparatus utilizing the pneumatic circuit of the above 
described construction operates in the following manner. 
Referring now to FIG. 2 showing the timing chart illustrating the sequence 
of operation of the work handling apparatus, a cycle of a grinding process 
includes a first suction handling step, a grinding step, a second suction 
handling step and a release step. During the first suction handling step, 
the work 1 is picked up by the suction holder 2 and is then processed to 
the processing tool; during the grinding of the work 1 step, the grinding 
is effected while the abrasive fluid is supplied to the work 1; during the 
second suction handling step, the work 1 which has been ground is picked 
up by the suction holder 2 and is separated from the processing tool; and 
during the release step, the work is released from the suction holder 2. 
Assuming that the vacuum pump 3 is continuously driven as a result of the 
supply of electric power thereto, and during the first suction handling 
step, the electromagnetic valve 4 is switched off to cause the valve to 
assume the suction position as shown with the suction holder 2 
consequently communicated with the vacuum pump 3 through the passages P1 
and P2, and the work 1 which has not yet been processed is picked up by 
the suction holder 2. When the electromagnetic valve 8 is subsequently 
switched on to the open position it activates both the pressure sensor 7 
and the vacuum gauge 9. Should at this time the suction holder 2 hold the 
work 1 properly, the pressure sensor 7 detects a negative pressure and is 
therefore switched on to issue a close signal therefrom. This close signal 
from the pressure sensor 7 is applied to the electromagnetic valve 8 to 
interrupt the supply of electric power thereto, causing the 
electromagnetic valve 8 to assume the closed position as shown. The 
electromagnetic valve 8 is controlled by a timer such that, unless the 
pressure sensor 7 fails to be switched on after a predetermined length of 
time subsequent to the pick-up of the work 1 onto the suction holder 2, no 
subsequent grinding step can take place. 
After the first suction handling step, the electromagnetic valve 4 is 
switched on to the release position in which the passage P1 is 
communicated with the compressed air source 5. At the time the 
electromagnetic valve 12 in the pneumatic passage P5 is subsequently 
switched off to assume the closed position simultaneously with the 
switching-on of the electromagnetic valve 4, the compressed air from the 
compressed air source 5 flows only through the pneumatic passage P4 via 
the flow regulator 10 and is then supplied to the suction holder 2 to 
release the work 1 therefrom in readiness for the next succeeding handling 
step. 
The flow regulator 10 is so adjusted as to allow the flow of compressed air 
therethrough at a rate considerably throttled as compared with the flow 
regulator 11 so that the air flow, at this time, is weak, as shown by the 
bottom line of FIG. 2. After the termination of the grinding step, the 
electromagnetic valve 4 is switched off to cut off the weak air flow and 
to assume the suction position to communicate the suction holder 2 with 
the vacuum pump 3 therethrough and, simultaneously therewith, the 
electromagnetic valve 8 is switched on to communicate both of the pressure 
sensor 7 and the vacuum gauge 9 with the pneumatic passage P1. In this 
condition, the work 1 which has been processed is picked up by the suction 
holder 2 to separate it from the processing tool. Substantially at the 
time of establishment of a vacuum in the passages P1 and P3, more 
specifically, substantially simultaneously with the timing at which the 
electromagnetic valve 8 is switched on, the pressure sensor 7 detects the 
presence of the negative pressure and is, therefore, switched on to issue 
the close signal which is applied to the electromagnetic valve 8 to cause 
the latter to assume the closed position as shown. 
Although a quantity of the abrasive fluid may be sucked through the suction 
nozzle 2 into the pneumatic passage P1 and then into the pneumatic passage 
P3 at an initial stage of the first suction handling step, that is, during 
a length of time subsequent to the time at which the electromagnetic valve 
8 is switched on in response to the switching-off of the electromagnetic 
valve 4 and prior to the time at which the electromagnetic valve 8 is 
switched off in response to the close signal supplied from the pressure 
sensor 7, the abrasive fluid entering the pneumatic passage P1 can be 
separated from air by the filter 13 and, therefore, does not flow further 
into the pneumatic passages P1 and P3. 
After the work 1 being processed has been picked up by the suction holder 2 
at the end of the second suction handling step, and in readiness for the 
removal of the processed work 1 from the suction holder 2, the 
electromagnetic valve 4 is switched on and, simultaneously therewith, the 
electromagnetic valve 12 is switched on to communicate the suction holder 
2 with the compressed air source 5 by way of the pneumatic passage P1 and 
both of the parallel pneumatic passages P4 and P5. As a result, a strong 
flow of compressed air is supplied to the suction holder 2 to eject the 
processed work 1. 
Although the present invention has been described in connection with the 
preferred embodiment thereof with reference to the accompanying drawings, 
it is to be noted that various changes and modifications will be apparent 
to those skilled in the art. For example, although reference has been made 
to the use of the vacuum pump as a source of vacuum, any other suitable 
source of vacuum may be employed. 
Also, although the use of the filters 13 and 14 for separating the abrasive 
fluid from air by the utilization of a difference in flow velocity has 
been described, they can be replaced with respective closed vessels of a 
volume greater than the volume of the associated passages. 
Accordingly, such changes and modifications are to be understood as 
included within the scope of the present invention as defined by the 
appended claims, unless they depart therefrom.