医疗器械疲劳试验系统的比较

在过去的二十年里，疲劳测试经历了几次重大的技术变革. 之前to1990, 几乎所有的疲劳试验机都采用伺服液压原理对试样施加载荷. Servohydraulics had been used since the mid-1950s and was the de facto standard technology when building material, 汽车, 航空航天, 大型结构测试器. 在20世纪90年代, manufacturer sstarted experimenting with other drive technologies including servopneumatics and linear motors.

而大多数21世纪的医疗设备测试应用利用直线电机技术, each technology possesses unique characteristics that make it indispensable to medical device testing.

伺服液压控制的(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s introduced the first servohydraulic test system when it was the Material Test 系统s Division division of Research Incorporated in the mid-1950s. MTS employed servovalve and hydraulic cylinder technologies designed for 航空航天 flight control systems and applied them to fatigue testing. 在那之前, 疲劳试验在旋转弯曲机或共振(弹簧/质量)试验系统上进行. The advantage of the new servohydraulic approach was that the loading “R” Ratio could be controlled to something other than -1.0.

另外, 所施加的载荷可以从几千牛顿到几百万牛顿, 加载通道的数量也是可扩展的. 例如, a simple fatigue tester might have only one loading actuator while an airplane wing test rig might have 30 to 40 actuators. 随着伺服液压测试系统市场的成熟，其他公司也进入了市场. 今天, 伺服液压测试系统的供应商包括MTS, Instron, 株式会社, 日本岛津公司, 西海岸和兹威克路口.

伺服液压执行器的大小可以满足几乎任何负载要求, 执行器几乎可以设计为任意行程(最常见的行程长度为100mm), 150mm或250mm). Servohydraulic actuators are also relatively easy to design; if you have a special stroke and force requirement, 一个新的定制执行器可以在几个小时内设计出来

然而，SH执行器可以设计的最小实际额定力约为5kN. 对于小于5kN的载荷，油封的摩擦会导致系统分辨率出现问题. 还有一个关于清洁度的问题——如果在测试过程中执行机构密封泄漏, 试验试样可能被污染.

另外, 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), 对于心血管设备来说，它不够耐用(4亿到6亿次循环). 也因为他们的设计, SH systems require a high powered (5HP minimum) hydraulic pump with an oil supply that must be regularly changed, 使它成为一个相对高维护的系统.

伺服气动(SP)测试系统

An SP test system is similar to the hydraulic test system except that it uses compressed air instead of hydraulic fluid as the driving media. EnduraTEC introduced these systems to the orthopedic market in the early 1990s as a lower cost alternative to the SH systems. 虽然SP系统有望在该市场领域产生影响, 它们没有在主流市场流行起来. A combination of limited performance frequency compared to a fluid-based system and the fact that most customers had already invested heavily in SH systems limited the impact of SP systems.

对于较低的力(i.e., 小于1kN)和中等测试频率(10hz或更低)的应用, SP系统是SH系统的可行替代方案. 唯一提供SP系统的制造商是EnduraTEC.

单相直线电机(SPLM)

Single Phase Linear Motors generate a force that is proportional to the amount of electrical current applied. In the mid-90s, EnduraTEC began delivering tests systems with voice coils for stent and wire testing. 专利5,670,708是一种使用两个音圈作为驱动手段的支架移植测试仪. 音圈后来被Bose公司开发的移动磁体直线电机所取代.

The moving magnet design was superior to the voice coil approach because it eliminated the flying leads which were prone to fatigue failure, 更容易冷却，运动质量更低. The moving magnet motor was also employed in the ElectroForce Fatigue Test Instruments supplied by EnduraTEC (later Bose and then TA Instruments).

SPLM systems are sometimes preferred because their low output force range is ideally suited for testing small medical devices developed for the intravascular market. 另外, 柔性轴承系统和移动磁铁设计提供了极高的寿命, and the power required to drive a SPLM is quite low compared to the power required to drive an SHor SP system. 因此，由于低运动质量，很容易获得60Hz及更高的测试频率.

然而, 与其他系统相比，SPLM系统的受力能力较低, and the amount of stroke that can be applied is generally limited and is dependent on the size of the SPLM. Another disadvantage is that the ability to readily customize SPLMs is almost non-existent due to the nature of the components used, 使一次性项目变得困难.

目前只有一家测试系统供应商使用移动磁铁splm, 这是TA仪器公司.

多相直线电机(MPLM)

第一台MPLM测试仪于1998年由MTS系统公司推出并获得专利. That system featured a horizontally-mounted linear motor that had a 100mm stroke with an air bearing support system. It was designed forprecision low force fatigue applications in the semiconductor and medicaldevice testing industries. 尽管设计先进, it did not mak emuch of an impact in the market most likely because it was a new technology that did not fit within the SH paradigm of MTS’s culture.

在21世纪初，EnduraTEC成功地引入了SPLM测试系统, 英斯特朗和MTS决定，他们需要提供一种电动测试系统替代方案. 在2000年代末, 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.

The multi-phase design of the linear motor enables it to provide higher loads and a longer overall stroke. 例如，最小的TA ElectroForceTest仪器额定功率为200N，额定功率为12.总行程5mm, 最小的Instron ElectroPuls测试仪器额定功率为1000N，行程为60mm. 虽然有人可能认为MPLM方法优于SPLM, there are relative advantages and disadvantages that the MPLM has with respect to the SPLM as follows.

MPLM系统的附加相位意味着电机可以产生更多的功率. 如果磁铁组件的尺寸相同, 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. MPLM还具有更长的冲程能力, makeing it easier to test longer specimens and to setup tests as the longer stroke provides more flexibility.

然而，MPLM系统有几个缺点. Since the moving armature in an MPLM has more coil or magnet assemblies, the moving mass is greater. 这意味着在高测试频率下, the vibration induced into the test bench or floor can be substantial if care is not taken to isolate the frame from the bench. 而SPLM在60Hz及以上的频率下运行非常舒适, MPLM系统通常难以实现高于30Hz的频率. 为了提供更长的总行程，MPLM系统具有滚子轴承支撑系统.

结论

im体育APP has a wide breadth of equipment including SH, SP, SPLM and MPLM test systems at its disposal. 设置测试时, 我们能够选择最适合所需测试条件的测试系统.

例如, if you want to test up to 15 specimens at high frequency (30Hz or greater) by applying a few millimeters of displacement, 我们将使用SPLM测试系统. If you want to test a single specimen at high loads and a lower test frequency we would look at using either an MPLM or SH based system. 凭借我们广泛的设备基础和在机械测试领域的丰富经验, 元件能够提供最可靠的测试条件.