Design and research of measuring system of clamping force of hemostats

doi:10.4236/jbise.2010.39123

Paper Menu >>

Journal Menu >>

J. Biomedical Science and Engineering, 2010, 3, 927-930

doi:10.4236/jbise.2010.39123 Published Online September 2010 (http://www.SciRP.org/journal/jbise/ JBiSE

Published Online September 2010 in SciRes. http:// www.scirp.org/journal/jbise

Design and research of measuring system of clamping force of

hemostats

Huifang Wang, Shuyi Wang, Ying Zhou, Jie Tan

School of Medical Instrument and Food Engineering, University of Shanghai for Science and Technology, Shanghai, China.

Email: [email protected]

Received 15 July 2010; revised 25 July 2010; accepted 28 July 2010.

ABSTRACT

Reliability of medical instruments such as hemostats

is extremely important because these instruments are

used in patients who are in critical condition. Clam-

ping force of hemostats, as an important parameter

of hemostats, should be detected. However, it could

not be tested directly. In order to test it, a testing sys-

tem has been put forward. The system is comprised

of sensor, acquisition card, and three-way tap and so

on. This system is controlled by a computer. The tes-

ting system has been proved to be effective in testing

the clamping force of hemostats.

Keywords: Hemostat; Clamping Force; Measuring Sys-

tem

1. INTRODUCTION

A hemostat is a vital surgical tool used in almost any su-

rgical procedure, usually to control bleeding. Hemostats

belong to a group of instruments that pivots (similar to

scissors, includes needle holders, tissue holders and var-

ious clamps), and where the structure of the tip determ-

ines their function. Hemostats have handles that can be

held in place by the locking mechanism. The locking

mechanism is typically a series of interlocking teeth, a

few on each handle that allow the user to adjust the cla-

mping tension of the pliers [1]. However, pressure val-

ues are different regarding to different hemostats.

Medical equipment manufacturers can produce many

kinds of hemostats, but inspection standard and inspec-

tion method of hemostats remain be not researched and

improved, especially clamping force of hemostats rem-

ains cannot be tested directly or indirectly. However,

clinicians or inspection personn el both hope to know the

quantitative pressure.

In both at home and abroad, clamp pressure measure-

ement has been fixed in the field of auto and robots. In

brake-by-wire systems of auto, central controllers requ-

ire accurate information about the clamp force between

the brake pad and the disc as a function of pad displ-

acement, which is usually denoted as the characteristic

curve of the caliper. Due to aging, temperature, and oth-

er environmental variations, caliper characteristic curves

vary with time. Therefore, automatic caliper calibration

in real-time is vital for high-performance braking action

and vehicle safety [2]. In robots, firstly design machine

gripper according to the features of the object of holding.

Secondly analyzes forces of all parts of machine gripper.

At last, derivate clamp pressure force according to the

principle of torque. In these machine grippers some are

two-finger translation grippers [3] and some are curved

arm type hydraulic grab with four bar linkage [4]. There

are hardly some studies in clamp pressure measurement

of hemostats.

Existing pressure sensors in shape and size and fatigue

resistance level are unable to satisfy the special needs of

these medicinal hemostats, so direct measurement of cla-

mping force of hemostats needs design special sensor

system. However the sensor system has not been worked

out so far according to my study. So some attentions

have been focused on finding an indirect measurement

method.

An indirect measurement method is proposed in this

paper. Through testing pressure changes of a clamping

catheter filled with liquid, clamping force of hemostats

can be reflected indirectly.

2. METHODS AND APPARATUS

2.1. Description of Apparatus

Measuring system of clamping force of hemostats is

designed which is shown in Figure 1.

The testing system can be divided into two parts acco -

rding to their different functions.

Part 1: In this part, hardware principle of the test syst-

em is provided. Functions of each component as follows:

1) Injector: Eliminate air and fill liquid in the whole

system.

H. F. Wang et al. / J. Biomedical Science and Engineering 3 (2010) 927-930

928

Figure 1. Structure of testing system of clamping force of hemostats.

2) Three-way tap 1: Make the whole system separate

from air.

3) Three-way tap 2: Used for the switch of calib ration

and testing of pressure.

4) Fluke 718 30G: Provide pressure to the system.

5) Catheter 1(Oxygen tubes) and hemostat (XAB010

made in Shanghai Medical Instruments (Group) Corp.,

Ltd. Surgical Instruments Factory): Clamp catheter one

using a hemostat.

6) Three-way tap 3: Test whether there is air or not,

and make sure there is no air in the whole system.

7) Three-way tap 4: Make liquid inject easily into the

whole system.

8) Collecting vessel: Collect the liqu id while injecting

liquid into the system.

9) Cathet er 2 : Any cathet er can be used.

Part 2: In this part, the interface between PC running

under Windows XP and sensor was realized through an

RS-232 connection. The sampling rate is controlled by

PC and software, which is based on Visual C++ 6.0

platform. The signal coming from sensor is obtained by

acquisition card, and then is transmitted to computer.

Last data signals could be displayed on monitor.

2.2. Measurements

The measurement is carried out using a test solution of

ISO class Ⅲ water for medical use, under normal cond-

ition (25˚C ± 2˚C, 58% ± 5% RH (Relative humidity)).

There are several steps to implement this apparatus:

First: Connect all the joints and check the testing sys-

tem. The whole system should be filled with water in

advance.

Second: Calibrate of the testin g system. Pressure sens-

or is an important part in testing system, and the accu ra-

cy and precision of sensor are influenced by actual envi-

ronment, such as temperature, relatively humidity. So to

ensure the accuracy of the testing result, pressure calibr-

ation of the sensor and the whole testing system is neces-

sary before testing.

Third: Test clamping force of hemostats. The real-time

pressure va l ue s could be di splayed in monitor .

3. RESULTS

In this testing system, pressure calibrator of Fluke-718

30 G which has ± 0.05% of range and resolution is 0.01

kPa was used, it can be used to calibrate pressure sensor

whose rang e of pressur e is 0-20 0 kPa and the wh ole test-

ing system [5].The unit of calibrator is kPa and computer

display is V (voltage), and computer display is the value

of pressure signal, which has been magnified and filter-

ed.

Based on the relationship between calibrator value and

computer display value, a line could be drawn. The rela-

tion between the display of computer and pressure cali-

brator is almost linear. The expression was calculated

with least squares approx imation and it is:

55.531 102.81yx





where x is the actual pressure obtained from an acquisi-

tion card and y is the value of calibrator.

Oxygen tubes (GB15593-1995) were repetitive tested

under the same condition, including temperature (25˚C ±

2˚C), relative humidity (58% ± 5%) and initial pressure

(30 kPa). In the testing system, a hemostat, which has

H. F. Wang et al. / J. Biomedical Science and Engineering 3 (2010) 927-930

929

Figure 2. Pressure values of different ratchets of hemostats.

five ratchets [6], was used. In Figure 2, 0 represents the

hemostat was not be used,1,2,3,4, and 5 represents re-

spectively the first, second, third, four th and fifth ratchet

was used. Pressure values of clamping force of hemo-

stats are shown in Figure 2. The average values of the

pressure of each ratchet are signed in the Figure 2. The

lines of 5 different colors represent that the repetitive

tests were performed 5 times.

4. DISCUSSION AND CONCLUSIONS

The drawing lines in Figure 2 are tested results of a he-

mostat and these tests are repeated implemented under

normal environment. From these drawing lines above,

the average value of the pressure of the first ratchet is

93.9913kPa, the second ratchet is 1 09.7438kPa, the th ird

ratchet is 117.5280 kPa, the fourth ratchet is 121.1528

kPa and the fifth ratchet is 123.4986 kPa. Some results

can also be obtained: when the second ratchet is used,

the error which is less than 3 kPa is maximal, and when

some ratchets are used, the data is nearly same. So to so-

me extent clamping force of hemostats can be reflected

indirectly. Thus in turn the testin g measure and system is

proved to be corrected.

The sensor is influenced by environment, especially

by temperature. In order to ensure the accuracy of the

test, calibration process should be implemented before

performance, even in stable environment, calibration

should be oper a t ed pe ri o di cal l y .

In this study the measuring system of clamping force

of hemostats is designed. The results of measuring sys-

tem of clamping force of hemostats have verified that

this method is efficient. In the testing, after doing an exp-

eriment, if another repeated experiment needs to be done,

experimenters need to wait for a period of time, at least 4

minutes, to make catheters restore deformation. The fu-

ture research is concerned with these following topics:

1) The system is influenced by environment, such as

temperature, relative humidity, so more tests should be

implemented to come to a much better relation between

system and environment, which can be a reference for

further tests.

2) In the past experiments only one kind of catheter

and only one hemostat was used. As we all know, there

are many kinds of catheters and hemostats. And if the

catheter is too soft and the pressure of the hemostat is

too high, the catheter is destroyed permanently and

ratchets of hemostats is useless. But if the catheter is too

rigid and the pressure of the hemostats is too low, there

is not tiny deformation after clamping catheters using

hemostats. The theory applies to clamp blood vessels

using hemostats. If vascular wall is too thin, but the

pressure of hemostats is too high, the blood vessels will

be ruptured. However if vascular wall is too thick and

the pressure of hemostats is too low, bleed will still flow

from blood vessels. Thus patients are very dan- gerous.

So it needs to further study to which hemostat matching

to which catheter.

5. ACKNOWLEDGEMENTS

The research described in this paper is being supported by Initial

Funding for Doctor of University of Shanghai for Science and Tech-

nology and supported by Funded Projects of Key Discipline of Shang-

hai, Project Number: T0502.

H. F. Wang et al. / J. Biomedical Science and Engineering 3 (2010) 927-930

930

REFERENCES

[1] http://www.answers.com/topic/hemostat

[2] Hoseinnezhad, R., Bab-Hadiashar, A. and Rocco, T. (2008)

Real-time clamp force measurement in electromechanical

brake calipers. IEEE Vehicular Technology Society, 57(2),

770-777.

[3] Su, Z.H. and Kong, Q.Z. (2008) Design of two- finger

translation gripper of articulated robot. Mechanical En-

gineering & Automation, (5), 80-84.

[4] Ma, Z.S., Bian, X.L. and Chu, X.J. (2008) Design and

performance simulation for grab on emergency engi-

neering robot. Engineering Machinery, 39(7), 25-28.

[5] Pressure Calibrator 718 Product.

[6] Zhang, H.Y., Li, B. and Xu, Z.T. (2008) Maintenance

and inspection of surgical instrument. Operation &

Maintenance, 29(9), 126.