Comparison of Medical Device Fatigue Test Systems

疲劳测试经历了几个主要的技术logy changes over the last two decades. Prior to1990, almost all fatigue testers used servohydraulic principles to apply load to the test specimen. Servohydraulics had been used since the mid-1950s and was the de facto standard technology when building material, automotive, aerospace, and large structural testers. In the 1990s, manufacturer sstarted experimenting with other drive technologies including servopneumatics and linear motors.

虽然大多数21世纪的医疗设备测试应用杠杆线性电机技术，但每种技术都具有独特的特性，使其成为医疗器械测试不可或缺的特性。

Servohydraulics (SH)

当大多数人想到伺服液压测试系统时，他们通常会想到MTS系统。MTS系统公司在20世纪50年代中期成立材料试验系统研究部时，引进了第一个伺服液压试验系统。MTS采用了为航天飞行控制系统设计的伺服阀和液压缸技术，并将其应用于疲劳试验。在此之前，疲劳试验要么在旋转弯曲机上进行，要么在共振（弹簧/质量）试验系统上进行。新的伺服液压方法的优点是加载“R”比可以控制到-1.0以外的其他值。

另外，施加的负载可以从几千杆棚缩放到几千克到几百万兆瓦，并且也可以缩放负载通道的数量。例如，简单的疲劳测试仪可能只有一个装载致动器，而飞机翼试验台可能具有30至40个致动器。随着伺服液试验系统的市场成熟，其他公司进入了市场。如今，伺服液试验系统的供应商包括MTS，Instron，Saginomiya，Shimadzu，Shore Western和Zwick。

伺服液致动器可以大小用于任何装载要求，并且致动器可以设计几乎任何行程（最常见的行程长度为100mm，150mm或250mm）。伺服液执行器也相对容易设计;如果您有一个特殊的笔划和力量要求，可以在几小时内设计一台新的定制执行器

However, the minimum practical force rating that a SH actuator can be designed to is about 5kN. For loads less than 5kN, the friction of the oil seals causes problems with the system resolution. There is also a concern with cleanliness - if the SH actuator seal leaks during testing, the test specimen can be contaminated.

Additionally, SH actuators are designed to last tens of millions of cycles without fatigue failures or seal leakage. While this level of longevity works well for the typical orthopedic test (up to 10 million cycles), it's not durable enough for cardiovascular devices (400 million to 600 million cycles). And because of their design, SH systems require a high powered (5HP minimum) hydraulic pump with an oil supply that must be regularly changed, making it a relatively high-maintenance system.

Servopneumatic (SP) Test Systems

SP测试系统类似于液压测试系统，除了它使用压缩空气而不是液压流体作为驱动介质。Enduratec将这些系统介绍到20世纪90年代初期的矫形市场，作为SH系统的较低成本替代品。虽然SP系统在这个市场区域产生了承诺，但他们在主流市场上没有抓住。与基于流体的系统相比的有限性能频率的组合以及大多数客户已经在SH系统中投入的事实限制了SP系统的影响。

Still, for lower force (i.e., less than 1kN) and moderate test frequency (10 Hz orless) applications, SP systems represent a viable alternative to SH systems. The only manufacturer that supplied SP systems was EnduraTEC.

单相直线电机（SPLM）

单相线性电动机产生与施加的电流量成比例的力。在90年代中期，Enduratec开始用用于支架和电线测试的音圈提供测试系统。专利5,670,708代表使用两个音圈作为驱动装置开发的支架移植测试仪。稍后用由Bose Corporation开发的移动磁铁线性电机替换语音线圈。

The moving magnet design was superior to the voice coil approach because it eliminated the flying leads which were prone to fatigue failure, was easier to cool and had a lower moving mass. The moving magnet motor was also employed in the ElectroForce Fatigue Test Instruments supplied by EnduraTEC (later Bose and then TA Instruments).

SPLM系统有时是优选的，因为它们的低输出力范围非常适合测试为血管内市场开发的小型医疗器械。另外，弯曲轴承系统和移动磁体设计提供极高的寿命，并且与驱动SHOR SP系统所需的电力相比，驱动SPLM所需的功率非常低。因此，由于低移动质量，容易获得测试频率60Hz和更高。

然而，与其他系统相比，SPLM系统具有低力能力，并且可以应用的行程量通常限制并且取决于SPLM的尺寸。另一个缺点是，由于所使用的组件的性质，难以使用的性质，即使使用的部件的性质困难，那么易于定制SPLM的能力几乎不存在。

目前只有一个使用移动磁铁剪线的测试系统供应商，这是TA仪器。

Multi-Phase Linear Motors (MPLM)

第一个MPLM测试仪于1998年由MTS系统引入和专利。该系统采用了一种水平安装的线性电动机，其具有100mm行程，带有空气支撑系统。它在半导体和医疗检测行业中设计了专注的低力疲劳应用。尽管其先进的设计，但在市场上的影响并不是最有可能的，因为它是一种新技术，这些技术不适合MTS文化的SH范式。

After the successful introduction of the SPLM test systems by EnduraTEC in the early 2000’s, Instron and MTS decided they needed to offer an electric test system alternative. In the late 2000s, Instron introduced its ElectroPulsSeries and in 2014 MTS introduced its Acumen Series of all-electric test instruments. Both systems feature a crosshead-mounted multi-phaselinear motor with a moving voice coil or magnet armature that is supported on a linear ball bearing system.

线性电机的多相设计使其能够提供更高的负载和更长的整体行程。例如，虽然最小的TA电磁体仪表在200N的额定速度并具有12.5mm的整体中风，但最小的Instron Electupuls Testinstrument在1000N时额定值，中风60mm。虽然人们可能认为MPLM方法将优于SPLM，但是MPLM相对于SPLM具有如下的相对优点和缺点。

The additional phases of MPLM systems mean the motor can generate more power. If the magnet assemblies are sized the same, a MPLM with three magnets (required for the multiphase motion) will generate twice as much force as an SPLM with a comparable-sized single magnet. The MPLM also has longer stroke capability, makeing it easier to test longer specimens and to setup tests as the longer stroke provides more flexibility.

There are several downsides to an MPLM system, however. Since the moving armature in an MPLM has more coil or magnet assemblies, the moving mass is greater. This means that at high test frequencies, the vibration induced into the test bench or floor can be substantial if care is not taken to isolate the frame from the bench. Whereas the SPLM is quite comfortable running at 60Hz and up, MPLM systems generally have difficulty achieving frequencies higher than 30Hz. To provide a longer overall stroke, the MPLM system features a roller bearing support system.

Conclusion

Element has a wide breadth of equipment including SH, SP, SPLM and MPLM test systems at its disposal. When setting up a test, we are able to choose the test system that is most appropriate for the desired test conditions.

例如，如果您想通过施加几毫米的位移在高频（30Hz或更高）下测试多达15个试样，我们将使用SPLM测试系统。如果您想在高负载和较低的测试频率下测试单个样本，我们将考虑使用基于MPLM或SH的系统。凭借我们广泛的设备基础和在机械测试领域的丰富经验，Element能够提供最可靠的测试条件。