¹ Center for Mechanical & Environmental Systems Technology (CMEST), University of Nevada, Las
   Vegas, Nevada, USA

In the field of personal protective equipment, gloves were being manufactured and marketed that claimed to significantly reduce the magnitude of vibration transmitted from vibrating tools to the hand. Most of these claims proved to be false. As a result, the International Organization for Standardization adopted ISO Standard 10819 to define test procedures that must be used to measure the vibration attenuation characteristics of gloves that were designed to reduce vibration into the hand.⁽¹⁾ This standard also specified the vibration attenuation values that must be achieved for a glove to be labeled as an "antivibration glove".

ISO Standard 10819 requires that test subjects exert a push force of between 50-60 N on the handle that directs vibration into their hand. At the same time, the electromechanical shaker to which the handle is attached must generate an overall vibration amplitude per pre-defined vibration spectra of up to 92.2 m/s². To meet these requirements, most laboratories that perform tests per the requirements of ISO Standard 10819 have used a large electromechanical shaker capable of producing dynamic forces in excess of 2000 N. These shaker systems, along with their power amplifies, are very expensive. In addition, a horizontal load cell that is placed in a platform on which the test subject stands has been used to measure the push force.

A project was undertaken at the Center for Mechanical & Environmental Systems Technology (CMEST) at the University of Nevada, Las Vegas in the USA to develop a test system that can be used to conduct glove vibration transmissibility tests per the requirements of ISO Standard 10819. The project had three objectives:

• The test system was to be inexpensive.

• The handle push force was to be measured at the electromechanical shaker, not at a platform on which a test subject stands.

• The transmissibility test results of selected gloves that were obtained with the inexpensive test system were to be compared with corresponding test results obtained from other laboratories that had been certified to conduct vibration transmissibility tests per ISO Standard 10819.

ISO STANDARD 10819 TEST PROCEDURES

ISO Standard 10819 specifies the test procedures that must be used to measure the vibration transmissibility of gloves.⁽¹⁾ The vibration transmissibility of a glove per ISO Standard 10819 is the ratio of the vibration amplitude directed into the palm of the hand inside of a glove divided by the vibration amplitude directed into the palm on the outside surface of the glove. The vibration signals that are measured at the handle and into the palm are the overall acceleration signals that are passed through an ISO weighting filter that is specified by ISO Standard 5349.⁽²⁾ Figure 1 shows the ISO weighting filter. The vibration transmissibility of a glove is a measure of the attenuation of vibration into the hand and arm by means of a resilient or vibration-damping material placed in the glove. The lower the vibration transmissibility, the more effective a glove is in reducing vibration energy into the hand and arm.

ISO Standard 10819 specifies the amplitude of vibration transmissibility that must be achieved for a glove to be classified as an antivibration glove. The standard requires the overall vibration transmissibility of a glove to be measured for mid frequencies (16-400 Hz) and for high frequencies (100-1,600 Hz). Figure 2 shows the third octave amplitudes of the vibration spectra for the mid and high frequency test signals, respectively. Vibration first corresponding to the mid frequency test spectra and then to the high frequency test spectra are directed into the hand by means of a 40 mm diameter handle attached to a vibration shaker. Sets of two measurements on each of three test subjects for a total of six measurements are made for each frequency range. Three different gloves, one for each test subject, are used for each series of tests. The six individual transmissibility values for both the mid and high frequency test signals are averaged to obtain the average ISO Standard 10819 vibration transmissibility values. The average mid-frequency transmissibility is designated TR_M, and the average high-frequency transmissibility is designated TR_H. For a glove to be classified as an antivibration glove:

• TR_M must be less than 1.0, and TR_H must be less than 0.6.

• The resilient or vibration-damping material must be placed in the palm and the full finger and thumb stalls of the glove.

TEST SETUP FOR ISO STANDARD 10819 TESTS

One of the major objectives of this project was to use a small electromechanical shaker that generates a maximum dynamic force of less than 230 N for the vibration transmissibility tests. In the past, these small shakers could not be used because their center coil cannot resist a push force of 50-60 N without bottoming the coil into the outer casing of the shaker.

Figure 3 shows a drawing of the electromechanical shaker setup that was designed and used for this project. The electromechanical shaker rests on top of an aluminum platform that is mounted on four linear roller bearings. In the absence of a restraining force, the platform is free to move in the direction of the push force that is applied to the shaker handle during a test. The platform is connected to a rigid aluminum post that is attached to the base of the setup by means of a small aluminum load ring. The load ring is used to measure the push force that is applied to the shaker handle during a test. The load ring is connected to the platform and to the rigid post by means of floating pin joints. The ends of the load ring loosely fit onto the pins. The pin joints have enough play in them to allow the load ring to sense zero strain when no push force is applied to the shaker handle and to react only to a strain that is associated with a push force that acts along the axis of the load ring. To prevent the shaker coil from bottoming into the outer casing of the shaker, an air bladder is placed between an extension from the back end of the coil and a rigid post that is attached to the shaker platform. The air bladder provides a very soft resilient element between the shaker coil and post that resists the push force. The presence of the air bladder does not significantly affect the dynamic properties of the shaker coil.

Figure 4  Load Ring

Figure 5  Handle Used to Measure Grip Force

Figure 5 shows a drawing of the shaker handle. The handle is used to direct vibration into the hand and to measure the grip force. The handle is designed so that it does not have a resonance frequency between the frequencies of 5 - 2,000 Hz. To ensure this, the handle has a minimum wall thickness of 6.5 mm. An offset strain gauge beam is inset into the handle so that the top surface of the beam is around 3-4 mm above the surface of the handle. The beam is placed into a shallow channel that is milled into the surface of the handle. A four-gauge strain gauge bridge is placed on the underside of the beam as is shown if Figure 5. The leads from the bridge are attached to a strain indicator. The output from the strain indicator is directed to a visual meter that can be monitored during a test. The meter is calibrated by applying a known point force to the center of the beam. The shaker handle is oriented so that the fingers compress the beam when the hand clasps the handle during a test. Thus, the beam is located opposite the accelerometer that is mounted in the handle to measure the acceleration amplitude directed into the hand from the handle during a test (Figure 3).

Two Endevco 2222c subminiature accelerometers were used to measure the handle acceleration and the acceleration into the hand. The accelerometer that was used to measure the handle acceleration was inset into the center of the shaker handle directly below the palm of the hand (Figure 3). The accelerometer that was used to measure the acceleration into the palm of the hand was inset into the hand adapter shown in Figure 6. The adapter is placed in the palm of the hand as shown in Figure 7 during a vibration transmissibility test. Each accelerometer was calibrated before each test with an accelerometer calibrator.

Figure 6  Adapter Used to Hold the Accelerometer in the Palm of the Hand

Figure 7 Placement of Adapter in the Palm of the Hand for a Vibration Transmissibility Test

TEST PROTOCOL FOR THE ISO 10819 TESTS

Figure 8 shows the system layout and Figure 9 shows a picture for the test setup that was used for the ISO 10819 tests that were conducted during this project. The mid and high frequency test spectra shown in Figure 2 were manually adjusted for the vibration transmissibility tests that were conducted. A signal from a pink noise generator was passed through a Butterworth bandpass filter to a third octave band graphic equalizer. The Butterworth filter corner frequencies were set at 16 Hz and 400 Hz for the mid frequency test signal and at 100 Hz and 1,600 Hz for the high frequency test signal. The third octave band values from the graphic equalizer were manually adjusted to achieve the mid and high frequency test signals that were required by ISO Standard 10819 for each series of tests. The signal from the graphic equalizer was then directed to the shaker amplifier and then to the shaker. With great difficulty, it was possible to maintain the test spectra shown in Figure 2 within the third octave frequency amplitude band limits that are specified in ISO Standard 10189 during a series test. Many test setups used a feedback vibration controller. When this is the case, the feedback vibration controller will replace the noise generator, Butterworth bandpass filter, and graphic equalizer.

Figure 8 System Setup for ISO Standard 10819 Tests

Figure 9 Picture of System Setup for ISO Standard 10819 Tests

The signals from the accelerometers were directed through their respective charge amplifiers to a B&K 2144 Dual-Channel Real Time Analyzer. The analyzer was used in the third octave frequency mode. The ISO weighting filter shown if Figure 1 was programmed into the analyzer for both of the accelerometer channels. The ratio of the amplitude of the ISO weighted acceleration into the hand divided by the amplitude of the ISO weighted acceleration at the handle was processed by the analyzer. The test signals from the charge amplifiers were recorded on two channels of an eight-channel DAT recorder for future processing, if necessary.

All tests were conducted per the test procedures that are specified in ISO Standard 10189. Three test subjects and three separate gloves were used for each series of tests.

TEST RESULTS

Seven different gloves that contained different vibration-damping materials were tested at CMEST using the test system setup shown in Figures 3 through 8 and the test protocol described above. Figure 10 shows a test in progress at CMEST. The same gloves were also tested at two European laboratories: Delta Acoustics & Vibration in Lyngby, Denmark, and Berufagenossenchaftliches Institut fur Arbeitssickerheit (BIA) in Sankt Asugustin, Federal Republic of Germany. Each laboratory used test protocols that were consistent with their respective interpretations of the test procedures specified in ISO Standard 10819. The test results for the tests that were conducted at CMEST, Delta Acoustics & Vibration, and BIA are shown in Table 1. The table indicates that the agreement in the ISO Standard 10819 test results from the three laboratories is very good.

• A test setup for conducting ISO Standard 10819 glove vibration transmissibility tests utilizing a small electromechanical shaker (maximum dynamic force < 230 N) has successfully been developed. It is possible to measure the push force applied to the shaker handle at the shaker with this test setup.

• The ISO Standard 10819 test results that were obtained with the test system that was developed during this project agreed very well with the corresponding test results that were obtained at Delta Acoustics and Light in Denmark and BIA in Germany.

1. ISO Standard 10819: Mechanical vibration and shock - Hand-arm vibration - Method for t he measurement and evaluation of the vibration transmissibility of gloves at the palm of the hand, 1996, International Organization for Standardization, Geneva, Switzerland.

2. ISO Standard 5349: Mechanical vibration - Guidelines for the measurement and the assessment of human exposure to hand-transmitted vibration, 1986, International Organization for Standardization, Geneva, Switzerland.

Paper presented at:
8th International Conference on Hand-Arm Vibration
Umea, Sweden
June 9-12,1998