A novel hydraulic force standard machine

Abstract

A hydraulic force standard machine covering the range 40 kN-1.5 MN has been designed, built and tested. Preliminary measurements indicate that this force standard can be self-calibrated to a relative standard uncertainty of 1 × 10 −4 or better and is linear to 0.31 kN. The design of this force standard is suitable for much larger machines generating forces up to 20 MN. The special features of this machine include the use of controlled clearance for the limitation of oil flow, thus enabling the generation of high pressures and large forces, the use of journal bearings external to the high-pressure region to give high stiffness against side thrusts, and a method of calibration that involves determining the slope of the curve force versus pressure. This calibration procedure is essentially a null method that is largely independent of load cell properties such as hysteresis, creep, long-term drift and state of calibration, in contrast to current build-up calibration techniques that are strongly dependent on load cell properties.

Calibration and measurement capability evaluation for 1 MN hydraulic force standard machine newly installed at NMIJ

“…This technique can achieve a relative expanded uncertainty of 5 × 10 −4 (coverage factor of k = 2) from 1 MN to 10 MN [10], but it depends on reference force transducers with long-term stability and minimal hysteresis and creep behavior. In contrast, the HFM, largely independent of force transducer characteristics such as hysteresis, creep, long-term drift, and calibration state [11], has a suitable mechanism for force generation up to 20 MN. Details of the HFM's advantages over the build-up technique can be found in the literature [11].…”

“…In contrast, the HFM, largely independent of force transducer characteristics such as hysteresis, creep, long-term drift, and calibration state [11], has a suitable mechanism for force generation up to 20 MN. Details of the HFM's advantages over the build-up technique can be found in the literature [11].…”

A low-friction high-load thrust bearing and the human hip joint

“…In the process of designing a force standard machine (McIlraith and Clarkson 2002), the need arose for a lowfriction thrust bearing operating at pressures up to 100 MPa. The accepted maximum operating pressures of the main types of hydrodynamic thrust bearings are about 30 times lower than this figure (Oberg et al 1982).…”

Collets and friction

“…Recently, collets have been used in a variety of circumstances in a force standard machine (McIlraith and Clarkson 2002). These collets were too large for trial and error methods of construction, so it was essential to find quantitative expressions for their properties if they were to be included as predictable elements in a detailed design.…”