Robert J. Jack

Six-degree-of-freedom whole-body vibration exposure levels during routine skidder operations

This research focuses on quantifying six-degree-of-freedom (6-DOF) whole-body vibration (WBV) exposure levels that occur in Northern Ontario skidders during routine field operating tasks. 6-DOF vibration running root-mean-square (RMS) acceleration levels at the operator/seat interface were determined for eight skidders while driving loaded, driving unloaded, picking up a load, dropping off a load and ploughing logs under field operating conditions. The acceleration data were weighted in accordance with ISO 2631–1:1997 and evaluated for both health and comfort outcomes. The mean running RMS weighted translational and rotational accelerations all exceeded 0.36 m/s2 and 0.14 rad/s2. The greatest average accelerations occurred while driving unloaded with this condition displaying translational vibration total values (VTV) that exceeded the upper limit of the ISO 2631–1:1997 health caution zone within an average of 2.3 h. Utilizing 6-DOF VTV, virtually all operating conditions would be designated as uncomfortable. Statement of Relevance: This study provides one of the most comprehensive reports on vibration exposures in seated vehicle operators. The results are geared towards ergonomists with discussions on health effects and measurement concerns, while providing the raw vibration exposure data that will be useful to vehicle, component and vibration sensor designers.

The effects of posture on seat-to-head Whole-body vibration transmission

Five male subjects were exposed to root-mean-square whole-body vibration (WBV) acceleration levels ranging from 0.011m/s2 to 0.615m/s2 while seated on a vibration simulator. During the WBV exposure, subjects adopted 5 unsupported trunk flexion/extension positions (15, 10, 0, −10 and −15, ±2.5 degrees from vertical), and 4 hip flexion positions (−10, 0, 10, and 20 degrees from the horizontal). WBV measurements were taken with a tri-axial accelerometer at the buttock/seat interface and the head. Hydrostatic weighing was also conducted to determine the subjects adipose content. Adipose content of the individual had no significant relationship with the seat-to-head transmission of vibration. Vibration exposures at 4Hz had significantly more transmission than vibration exposures at 6.3Hz. Vibration exposures in the Z-axis (vertical) had significantly more vibration transmission than vibration exposures in the X- (front-to-back) and Y-axes (left-to-right). A significant interaction was also found between trunk position, frequency and axis of exposure.

A Review of Factors Influencing Whole-Body Vibration Injuries in Forestry Mobile Machine Operators

Abstract Mobile machine operators in the forestry industry are subjected to long hours of whole-body vibration exposure while adopting static seated postures and performing repeated hand and foot movements to operate controls. These conditions have been found to put operators at increased risk for musculoskeletal injuries and pain in the neck, shoulders, and back, as well as decreased productivity. This paper provides a review of the individual risk factors for these musculoskeletal problems and explores the possible interactions between risk factors and their effects on injury and productivity. Gaps in the literature and directions for future research are identified and discussed.

Quantification of 6-Degree-of-Freedom Chassis Whole-Body Vibration in Mobile Heavy Vehicles Used in the Steel Making Industry

Whole-body vibration (WBV) of mobile machines used in the steel making industry has not previously been quantified in six-degrees-of-freedom (6DOF). The purpose of this paper was to quantify 6DOF vibrations during the daily operating tasks of 5 commonly used mobile machines types used in the steel making and metal smelting industries. Vibration data were recorded from the chassis of five commonly used mobile machines using a MEMSense MAG3 triaxial accelerometer & gyroscope (MEMSense, SD, USA), and analyzed using custom MatlabTM code. Elevated values were observed at the chassis for crest factors, peak running root mean squared accelerations, and vibration total values, resulting in ISO 2631–1 (1997) comfort predictions ranging from Uncomfortable to Extremely Uncomfortable. Vibration dominant frequencies were generally between 1 and 8Hz. A second peak which occurred at approximately 27 Hz was observed for each vehicle in almost all axes. Occurring at a frequency that has the potential to produce negative health effects, this second peak was probably caused by the engine idling or running at low speeds. Field vibration profiles from this study have been used as inputs to a 6DOF robot for use in a corresponding laboratory study designed to optimize seat selection thus allowing the steel making and other similar industries to select operator seats based on industry specific field vibration characteristics.

Selecting seats for steel industry mobile machines based on seat effective amplitude transmissibility and comfort

OBJECTIVE The purpose of this work was to help a steel industry partner select the most appropriate of three high end heavy equipment seats to retrofit a number of their heavy mobile machines used in the steel making process. PARTICIPANTS The participants included 8 males (22.3 ± 2.0 yrs.) and 8 females (23.5 ± 1.8 yrs.) with no experience operating heavy mobile equipment. METHODS Previously recorded 6-DOF chassis acceleration data from a Pot Hauler (a machine which picks up and transports pots of slag) were used to extract six, 20 second representative profiles for implementation on a lab-based heavy machine simulator (6-DOF Parallel Robotics System Corporation robot). Subjects sat on three heavy equipment seats (BeGe7150, Grammar MSG 95G1721, and a 6801 Isringhausen with the seat pan cushion retrofitted with a Skydex cushion) mounted on the simulator. Each subject completed three trials for each combination of seat (n=3) and vibration profile (n=6). Chassis and operator/seat interface vibration were measured by 2, 6-DOF vibration transducers. Variables included Seat Effective Amplitude Transmissibility (SEAT) (X,Y,Z,Roll,Pitch,Yaw,6DOF Vector Sum) to determine if the seat was attenuating or amplifying the vibration, 6-degree of freedom (DOF) vibration total value weighted predicted comfort (Avc) (according to ISO 2631-1) and operator reported comfort (ORC). RESULTS Factorial ANOVAs revealed significant differences (p < or = 0.05) between seats for all SEAT variables but different seats performed better than others depending on the axis. Significant differences between males and females were observed for SEAT in X,Y, and Pitch as well as for Avs. As expected there were significant differences between vibration profiles for all assessed variables. A number of interaction effects were observed, the most frequently occurring of which was between seat and vibration profile. CONCLUSIONS Based upon the number of seat and vibration profile interactions, results suggest that a single seat is not suited for all tested conditions. However, SEAT values for all of the seats tested were extremely low (e.g., 6-DOF SEAT < 30%) indicating that all of the seats were capable of providing good vibration attenuation.

The Use of Multiple Resolution Cross-Correlations to Align Simultaneously Collected Whole-Body Vibration Data

A multiple resolution cross-correlation (MRXcorr) procedure was created to align 6-degree-of-freedom (DOF) whole-body vibration (WBV) data time histories collected at the operator/set interface (OSI) and chassis of mobile forestry machinery. Three validation tests were conducted to substantiate the use of the MRXcorr. The results of these validation tests indicate that the MRXcorr can accurately determine the phase shift between two identical 6-DOF data time histories, as well as the phase shift between the 6-DOF chassis and simulated 6-DOF OSI data time histories for forestry skidders. The MRXcorr was also found to align actual field 6-DOF WBV data sets collected on the OSI and chassis of three forestry skidders better than a cross-correlation utilizing the entire length of the data time histories with r2-values from regression analyses between the two time histories being greater when those time histories were aligned with the MRXcorr 83.6% of the time.

Using a High Resolution Motion Capture System to Determine 6-DOF Whole-body Vibration Accelerations

Comprehensive investigations of the human response to vibration require many markers, accelerometers, and electrodes. The use of multiple measurement systems can result in time intensive subject preparation, large memory requirements for data storage and processing, skin motion artifacts, and subject encumbrance. The purpose of this study was to determine if a VICON™ motion capture system could reliably and accurately measure translational and rotational acceleration levels produced by mobile machines, thereby eliminating the need for accelerometers and potentially minimizing the aforementioned problems. Simulating these vibration exposures in a laboratory, it was found that translational displacements ≥ 0.1 mm produced absolute peak and RMS average acceleration measurement differences less than 5% between the VICON™ system and an accelerometer. The absolute peak and RMS rotational accelerations determined by the VICON™ system and those produced by a PRSCO™ hexapodrobot differed by 5.44 ± 3.87% and 3.57 ± 2.44% respectively. Accounting for the vibration attenuation of the human body, the VICON™ system also appears well suited for determining 6-DOF acceleration levels in laboratory seat-to-head vibration transmission studies.

Reducing whole-body vibration through field vibration tested heavy equipment seat retrofitting

BACKGROUND: Heavy mobile equipment operation exposes operators to whole-body vibration (WBV) through the seat. The decision of which seat to retrofit a machine with is usually done statically. OBJECTIVE: To report on the third phase of a three phase project designed to intelligently retrofit seats in heavy mobile machines with the purpose of reducing machine operator WBV exposure. METHODS: Three slag pot haulers were retrofitted with a 6801 Isringhausen seat in which the seat pan cushion was retrofitted with Skydex TM seating material. Vibration dose values (weighted for health), vibration total values (weighted for comfort) and Seat Effective Amplitude Transmissibility were determined from field measurements. RESULTS:WBV was reduced from the first field study to below the upper boundary of the ISO 2631-1 (1997) health guidance caution zone and comfort weighted vibration total values were reduced to the second lowest discomfort rating. CONCLUSIONS: Steel making and other similar industries have been provided with information to more efficiently retrofit existing machines.

Whole-Body Vibration Sensor Calibration Using a Six-Degree of Freedom Robot

Exposure to whole-body vibration (WBV) is associated with a wide variety of health disorders and as a result WBV levels are frequently assessed. Literature outlining WBV accelerations rarely address the calibration techniques and procedures used for WBV sensors to any depth, nor are any detailed information provided regarding such procedures or sensor calibration ranges. The purpose of this paper is to describe a calibration method for a 6 DOF transducer using a hexapod robot. Also described is a separate motion capture technique used to verify the calibration for acceleration values obtained which were outside the robot calibration range in order to include an acceptable calibration range for WBV environments. The sensor calibrated in this study used linear () calibration equations resulting in values greater than 0.97 for maximum and minimum acceleration amplitudes of up to ±8 m/s2 and maximum and minimum velocity amplitudes up to ±100°/s. The motion capture technique verified that the translational calibrations held for accelerations up to ±4 g. Thus, the calibration procedures were shown to calibrate the sensor through the expected range for 6-DOF WBV field measurements for off-road vehicles even when subjected to shocks as a result of high speed travel over rough terrain.