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A rolling diaphragm hydraulic micro-manipulator
184
ELECTROENCEPHALOGRAPHY AND CLINICAL NEUROPHYSIOLOGY
TECHNICAL A ROLLING
NOTES
DIAPHRAGM
HYDRAULIC
MICRO.MANIPULATOR
1
ARTHUR LUTZ AND IRVING H . WAGMAN
Biomechanics Laboratory, University of California, San Francisco Medical Center, San Francisco 22, Calif. (U.S.A.) (Accepted for publication: June 18, 1964) The reliability of a hydraulic manipulator depends chiefly upon the maintenance of an air-free, leakproof, fluid transmission system. Introduction of even minute amounts of air into the hydraulic medium causes it to become compressible (spongy), and lag and backlash result, with an attendant loss of accuracy and reliability. The difficulty in maintaining a leak-free system is usually a result of unsatisfactory piston-cylinder fit. However, even the most accurately fitted piston invariably leaks, because of the necessarily imperfect wiping action of the piston against the cylinder wall. The use of "0" rings and other types of high pressure seal has not been found satisfactory, since they require the use of high operating pressures. Such pressures result in non-linearity, thus limiting the accuracy of the instrument. In order to obviate the difficulties encountered in previous hydraulic systems, we have incorporated a rolling diaphragm leak seal in the construction of a lightweight, highly accurate hydraulic manipulator, requiring little maintenance and using water as its transmission medium.
The rolling diaphragm seal Rolling diaphragms are relatively recent developments. In application they resemble a long-travel bellows. They possess the following properties: very low hysteresis, zero leakage, and sensitivity to slight pressure variations. Fig. 1 illustrates the position and action of a rolling diaphragm. As pressure is increased in the loading chamber, the piston is forced downward, causing the diaphragm (made of rubberized fabric) to roll off the piston side-wall and on to the cylinder wall with a lowfriction, leak-free action. CONSTRUCTION AND OPERATION The present manipulator employs two identical cylinders, each fitted with a rolling diaphragm seal and coupled together by water-filled flexible tubing. Coarse and fine mechanical drive units are added. Fig. 2 illustrates such an arrangement. Movement imparted to the piston shaft 1 Supported by National Institutes of Health research grant GM 08013.
Fig. 1 With downward displacement of the piston, the diaphragm rolls off the piston side-wall onto the cylinder wall. Fluid leakage is precluded.
of the driver unit by operation of the coarse or fine drive is transmitted to the micro-electrode affixed to the piston shaft of the electrode unit. Transmission is accomplished via the water within the nylon tubing. Since leakage is eliminated and friction is minimal, extremely small movements of the micrometer head will be faithfully followed by the micro-electrode with a reproducible accuracy of within 0.5 /~, with zero backlash and zero creepage, as measured under the microscope. Gross ~.xcursions of the electrode are accomplished by use of the coarse drive. Maximal movement is limited by the size of the diaphragm employed. Once filled with fluid, the device becomes a selfcontained unit requiring no subsequent filling. The major cause of air-bubble formation in other hydraulic systems is eliminated by use of the diaphragm seal. Tubing lengths of as much as 2 m have been used with no measurable transmission lag. During use, inadvertent movement of the tubing does not affect electrode position. Nylon quick-disconnect tube fittings are used to maintain leak-tight connection between tubing and cylinders. Linear motion ball bearings eliminate lateral play in the piston
Eleetroenceph. clin. Neurophysiol., 1965, 18:184-186
HYDRAULIC MICRO-MAN1PULATOR
ELECTRODE UNIT
18 5
DRIVER UNIT NYLON TUBING MICROMETER HEAD FINE DRIVE MICROMETER SPINiLE
~~\'~\\"~
'tgR"o",NG O,AP.R;; OISTON
~
~
"
LINEAR MOTION BALL BEARING
i
~
PI
II I
E: mt-t
HP'
l~: HI
p.~.~ ~.,. I I I ...... ?y~----~l "1--I- COARSE DR,VE
~
PISTON SIqAFT LUER LOCK CONNECTOR N ,-II,,TO RECORDER /MICROELECTRODE I
~
..........
,JL" ~
~ I~
I
I I-"I I ]
Fig. 2 Cutaway drawing of rolling diaphragm hydraulic micro-manipulator. Movement imparted to the piston shaft of the driver unit by the coarse or fine mechanical drive is transmitted to the microelectrode affixed to the piston shaft of the electrode unit. (Accuracy within 0.5 if).
Fig. 3 Rolling diaphragm hydraulic micro-manipulator. The cylinders of the electrode and driver units are approximately 3 1/2 in. (9 cm) long and 1 3/16 in. (3 cm) in diameter.
shafts (Teflon bushings have also been used successfully). A return spring in the electrode unit maintains pressure against the micrometer spindle when the driving direction is reversed.
Micro-electrode attachment can be made in various ways. In the instrument illustrated in Fig. 2 and 3, a tungsten or steel micro-electrode is crimped into the barrel of a standard hypodermic needle. The needle is
Electroenceph. clin. Neurophysiol., 1965, 18 : 184-186
186
A. LUTZ AND I. H. WAGMAN
then fitted to the piston shaft by a Luer-Lok connection, and a recording lead wire clipped to the needle hub. Electrodes are thus easily removable. The entire electrode unit may be operated in any position, and may be affixed rigidly in a variety o f holders. F o r intracranial recording, a satisfactory method is to attach it to a stereotaxic electrode carrier by a simple clamping arrangement. MATERIALS
Diaphragm 1. The size of the diaphragm determines the dimensions o f the cylinders and the m a x i m u m electrode travel. The smallest diaphragm available is 1"4 in. (6.3 ram) in diameter, allowing construction o f a cylinder 12 x 25 ram, with an electrode travel o f 5 mm. The present manipulator uses a diaphragm 1 in. (25.4 ram) in diameter, and has an electrode travel of 30 ram. Cylinder assemblr. The Bellofram manual supplies all dimensions necessary for machining o f cylinders. Tolerances are relatively wide: ~ 0.005 in. (0.13 mm). The cylinders shown in Fig. 3 have an outside diameter of 1 3/16 in. (3 cm) and a height o f 3 1~2 in. (9 cm), and are identical in all dinaensions. They are made o f Plexiglas. Pistons are o f aluminum, and piston shafts are o f 1/4 in. (6.3 ram) ground stainless steel shafting. Linear-motion ball bushings ~ reduce friction to a minimum and eliminate undesirable lateral motinn o f the shafts. Fhdd transmission system. 1000 psi (70.3 kg/cm e) hard-wall nylon tubing, with a 1/8 in. (3.2 ram) outside diameter, is used to couple the cylinders together. Swagelok nylon tube fittings a atop each cylinder provide leaktight tube-to-cylinder connection. Filling the system is relatively easy. Degassed distilled water is employed as the transmission fluid (water has a low coefficient o f friction, and its use is possible because rolling diaphragms eliminate the need for piston-cylinder lubricants). Any bubbles remaining after filling dissolve within 24 h. N o subsequent filling is required. Manufactured by Bellofram Corporation, Blanchard Road, Burlington, Mass. 2 Manufactured by T h o m s o n Industries, Inc., Manhasset, New York. a Manufactured by Crawford Fitting Co., 884 East 140th Street, Cleveland 10, Ohio. 4 Manufactured by W. R. Prior and Co., Ltd., L o n d o n Road, Bishop's Stortford, Herts., England. a Manufactured by Moore and Wright, Ltd., Sheffield, England.
Coarse andfine drives. The coarse-drive unit is a rackand-pinion type vertical limb section o f a mechanical manipulator 4. To it is rigidly affixed the micrometer drive-head ~ which is calibrated in 2 / I divisions and which has a 25 mm excursion. Movements as small as 0.5 /t are estimable with this unit. General features. The electrode unit section of the manipulator weighs 150 g. The entire instrument requires minimal servicing care. It has been used successfully in this laboratory to record, in acute experiments, single cell activity in the cortex, subcortical structures, and spinal cord and ganglia o f the cat. With the animal mounted properly, we have maintained single units for periods as long as 1 h. For use with chronic preparations, a smaller instrument o f similar design was constructed. The electrode unit o f this instrument can be easily mounted to the head o f an unrestrained, alert animal by means of fittings permanently implanted in a manner similar to that described by Hubel (1959). In such a preparatk)n, recordings o f single unit activity can be made on separate occasions over a period of weeks, with the instrument being detached after each session. One other feature o f the system (and one which is exclusive to hydraulic systems) should be noted. It is possible, by using cylinders of unequal size, to obtain magnification or reduction o f electrode movement relative to the driving-unit movement. F o r example, if the diameter of the driver piston were half that of the electrode unit piston, a 1 / / movement imparted to the driver shaft would produce a 1/4/~ movement o f the electrode. SUMMARY The construction is described o f a versatile, lightweight, and highly accurate hydraulic micro-manipulator, for use in acute neurophysiological experimentation. The instrument incorporates a rolling-diaphragm leak seal, uses water as its transmission medium, and requires minimal servicing care. A smaller instrument o f similar design for use with chronic preparations is also briefly described. REFERENCE HUBEL, D. H. Single unit activity in striate cortex o f unrestrained cats. J. Physiol. (Lond.), 1959, 147:226 238.
Reference: LUTZ, A. and WAGMAN,I. H. A rolling diaphragm hydraulic micro-manipulator. Electroenceph. clin. Neurophysiol., 1965, 18: 184-186.
ELECTROENCEPHALOGRAPHY AND CLINICAL NEUROPHYSIOLOGY
TECHNICAL A ROLLING
NOTES
DIAPHRAGM
HYDRAULIC
MICRO.MANIPULATOR
1
ARTHUR LUTZ AND IRVING H . WAGMAN
Biomechanics Laboratory, University of California, San Francisco Medical Center, San Francisco 22, Calif. (U.S.A.) (Accepted for publication: June 18, 1964) The reliability of a hydraulic manipulator depends chiefly upon the maintenance of an air-free, leakproof, fluid transmission system. Introduction of even minute amounts of air into the hydraulic medium causes it to become compressible (spongy), and lag and backlash result, with an attendant loss of accuracy and reliability. The difficulty in maintaining a leak-free system is usually a result of unsatisfactory piston-cylinder fit. However, even the most accurately fitted piston invariably leaks, because of the necessarily imperfect wiping action of the piston against the cylinder wall. The use of "0" rings and other types of high pressure seal has not been found satisfactory, since they require the use of high operating pressures. Such pressures result in non-linearity, thus limiting the accuracy of the instrument. In order to obviate the difficulties encountered in previous hydraulic systems, we have incorporated a rolling diaphragm leak seal in the construction of a lightweight, highly accurate hydraulic manipulator, requiring little maintenance and using water as its transmission medium.
The rolling diaphragm seal Rolling diaphragms are relatively recent developments. In application they resemble a long-travel bellows. They possess the following properties: very low hysteresis, zero leakage, and sensitivity to slight pressure variations. Fig. 1 illustrates the position and action of a rolling diaphragm. As pressure is increased in the loading chamber, the piston is forced downward, causing the diaphragm (made of rubberized fabric) to roll off the piston side-wall and on to the cylinder wall with a lowfriction, leak-free action. CONSTRUCTION AND OPERATION The present manipulator employs two identical cylinders, each fitted with a rolling diaphragm seal and coupled together by water-filled flexible tubing. Coarse and fine mechanical drive units are added. Fig. 2 illustrates such an arrangement. Movement imparted to the piston shaft 1 Supported by National Institutes of Health research grant GM 08013.
Fig. 1 With downward displacement of the piston, the diaphragm rolls off the piston side-wall onto the cylinder wall. Fluid leakage is precluded.
of the driver unit by operation of the coarse or fine drive is transmitted to the micro-electrode affixed to the piston shaft of the electrode unit. Transmission is accomplished via the water within the nylon tubing. Since leakage is eliminated and friction is minimal, extremely small movements of the micrometer head will be faithfully followed by the micro-electrode with a reproducible accuracy of within 0.5 /~, with zero backlash and zero creepage, as measured under the microscope. Gross ~.xcursions of the electrode are accomplished by use of the coarse drive. Maximal movement is limited by the size of the diaphragm employed. Once filled with fluid, the device becomes a selfcontained unit requiring no subsequent filling. The major cause of air-bubble formation in other hydraulic systems is eliminated by use of the diaphragm seal. Tubing lengths of as much as 2 m have been used with no measurable transmission lag. During use, inadvertent movement of the tubing does not affect electrode position. Nylon quick-disconnect tube fittings are used to maintain leak-tight connection between tubing and cylinders. Linear motion ball bearings eliminate lateral play in the piston
Eleetroenceph. clin. Neurophysiol., 1965, 18:184-186
HYDRAULIC MICRO-MAN1PULATOR
ELECTRODE UNIT
18 5
DRIVER UNIT NYLON TUBING MICROMETER HEAD FINE DRIVE MICROMETER SPINiLE
~~\'~\\"~
'tgR"o",NG O,AP.R;; OISTON
~
~
"
LINEAR MOTION BALL BEARING
i
~
PI
II I
E: mt-t
HP'
l~: HI
p.~.~ ~.,. I I I ...... ?y~----~l "1--I- COARSE DR,VE
~
PISTON SIqAFT LUER LOCK CONNECTOR N ,-II,,TO RECORDER /MICROELECTRODE I
~
..........
,JL" ~
~ I~
I
I I-"I I ]
Fig. 2 Cutaway drawing of rolling diaphragm hydraulic micro-manipulator. Movement imparted to the piston shaft of the driver unit by the coarse or fine mechanical drive is transmitted to the microelectrode affixed to the piston shaft of the electrode unit. (Accuracy within 0.5 if).
Fig. 3 Rolling diaphragm hydraulic micro-manipulator. The cylinders of the electrode and driver units are approximately 3 1/2 in. (9 cm) long and 1 3/16 in. (3 cm) in diameter.
shafts (Teflon bushings have also been used successfully). A return spring in the electrode unit maintains pressure against the micrometer spindle when the driving direction is reversed.
Micro-electrode attachment can be made in various ways. In the instrument illustrated in Fig. 2 and 3, a tungsten or steel micro-electrode is crimped into the barrel of a standard hypodermic needle. The needle is
Electroenceph. clin. Neurophysiol., 1965, 18 : 184-186
186
A. LUTZ AND I. H. WAGMAN
then fitted to the piston shaft by a Luer-Lok connection, and a recording lead wire clipped to the needle hub. Electrodes are thus easily removable. The entire electrode unit may be operated in any position, and may be affixed rigidly in a variety o f holders. F o r intracranial recording, a satisfactory method is to attach it to a stereotaxic electrode carrier by a simple clamping arrangement. MATERIALS
Diaphragm 1. The size of the diaphragm determines the dimensions o f the cylinders and the m a x i m u m electrode travel. The smallest diaphragm available is 1"4 in. (6.3 ram) in diameter, allowing construction o f a cylinder 12 x 25 ram, with an electrode travel o f 5 mm. The present manipulator uses a diaphragm 1 in. (25.4 ram) in diameter, and has an electrode travel of 30 ram. Cylinder assemblr. The Bellofram manual supplies all dimensions necessary for machining o f cylinders. Tolerances are relatively wide: ~ 0.005 in. (0.13 mm). The cylinders shown in Fig. 3 have an outside diameter of 1 3/16 in. (3 cm) and a height o f 3 1~2 in. (9 cm), and are identical in all dinaensions. They are made o f Plexiglas. Pistons are o f aluminum, and piston shafts are o f 1/4 in. (6.3 ram) ground stainless steel shafting. Linear-motion ball bushings ~ reduce friction to a minimum and eliminate undesirable lateral motinn o f the shafts. Fhdd transmission system. 1000 psi (70.3 kg/cm e) hard-wall nylon tubing, with a 1/8 in. (3.2 ram) outside diameter, is used to couple the cylinders together. Swagelok nylon tube fittings a atop each cylinder provide leaktight tube-to-cylinder connection. Filling the system is relatively easy. Degassed distilled water is employed as the transmission fluid (water has a low coefficient o f friction, and its use is possible because rolling diaphragms eliminate the need for piston-cylinder lubricants). Any bubbles remaining after filling dissolve within 24 h. N o subsequent filling is required. Manufactured by Bellofram Corporation, Blanchard Road, Burlington, Mass. 2 Manufactured by T h o m s o n Industries, Inc., Manhasset, New York. a Manufactured by Crawford Fitting Co., 884 East 140th Street, Cleveland 10, Ohio. 4 Manufactured by W. R. Prior and Co., Ltd., L o n d o n Road, Bishop's Stortford, Herts., England. a Manufactured by Moore and Wright, Ltd., Sheffield, England.
Coarse andfine drives. The coarse-drive unit is a rackand-pinion type vertical limb section o f a mechanical manipulator 4. To it is rigidly affixed the micrometer drive-head ~ which is calibrated in 2 / I divisions and which has a 25 mm excursion. Movements as small as 0.5 /t are estimable with this unit. General features. The electrode unit section of the manipulator weighs 150 g. The entire instrument requires minimal servicing care. It has been used successfully in this laboratory to record, in acute experiments, single cell activity in the cortex, subcortical structures, and spinal cord and ganglia o f the cat. With the animal mounted properly, we have maintained single units for periods as long as 1 h. For use with chronic preparations, a smaller instrument o f similar design was constructed. The electrode unit o f this instrument can be easily mounted to the head o f an unrestrained, alert animal by means of fittings permanently implanted in a manner similar to that described by Hubel (1959). In such a preparatk)n, recordings o f single unit activity can be made on separate occasions over a period of weeks, with the instrument being detached after each session. One other feature o f the system (and one which is exclusive to hydraulic systems) should be noted. It is possible, by using cylinders of unequal size, to obtain magnification or reduction o f electrode movement relative to the driving-unit movement. F o r example, if the diameter of the driver piston were half that of the electrode unit piston, a 1 / / movement imparted to the driver shaft would produce a 1/4/~ movement o f the electrode. SUMMARY The construction is described o f a versatile, lightweight, and highly accurate hydraulic micro-manipulator, for use in acute neurophysiological experimentation. The instrument incorporates a rolling-diaphragm leak seal, uses water as its transmission medium, and requires minimal servicing care. A smaller instrument o f similar design for use with chronic preparations is also briefly described. REFERENCE HUBEL, D. H. Single unit activity in striate cortex o f unrestrained cats. J. Physiol. (Lond.), 1959, 147:226 238.
Reference: LUTZ, A. and WAGMAN,I. H. A rolling diaphragm hydraulic micro-manipulator. Electroenceph. clin. Neurophysiol., 1965, 18: 184-186.