Example 1: Imagine a football team practising penalty kicks. Assuming the goal posts on both the ends to be the specification(spec) limits. The players think that putting the ball in between the posts is a goal (which it is). But the coach would like his/her wards to be highly consistent. He/she would expect his/her wards to

Twisted Nematicvs IPS

USL=24; LSL=18;Ave=21.5;Standard Deviation = 0.75. As per the given calculator, we get the values of Cp as 1.33 and Cpk as 1.11.

An application oriented question on the topic along with responses can be seen below. The best answer was provided by R Rajesh on 16th October 2018.

Overall this looks like an existing process which has been just satisfying the needs but has potential to increase its capability & maturity.

It means process is capable of  making parts within specification limit as Cp =1.33 whereas Cpk=1.11 we can say that process  is not centered as Cpk not equal to Cp i.e it is  closure to one of the specification limit i.e either USL or LSL

So here comes factor of Cpk which uses mean and SD to estimate probability. k is the amount of which a distribution is centred and Cpk tells the information about process mean. Cpk can never exceeds Cp value

over a period of stable operations . A capable process is one in which the output always adheres to the customer specifications.

Twisted nematicdisplay

Cpk takes the lesser of the two values. The formulas related to this are Cpku=(USL-XBAR)/(3*SD); Cpkl=(XBAR-LSL)/(3*SD) where SD is Standard Deviation and is actually denoted by 'Sigma' symbol.  Taking the lesser of the two values, the Cpk value would be Min(Cpku,Cpkl).

LCD Operating Modes Twisted Nematic (TN),  Super Twisted Nematic (STN), Film Compensated STN (FSTN), and Color STN (CSTN) are the terms used to describe four types of Liquid Crystal Displays, each twisting the orientation of the light passing through the Liquid Crystal Display structure differently to effect contrast and coloration. We also compare coloration, viewing angles, and costs between the technologies.   TWISTED NEMATIC (TN) LCDs TN displays have a twist ( the rotation of the molecules from one plane of the display to the other) of 90 degrees or less. All passive direct drive , active matrix, and most passive low level (x2 to x32) multiplexed LCD's have a 90 degree twist. The basic Twisted Nematic (TN) LCD consists of a layer of liquid crystal material supported by two glass plates. The liquid crystal material is a mixture of long, cylindrically shaped molecules with different electrical and optical properties, depending on direction On the inner surfaces of the glass plates are transparent electrodes, which are patterned to form the desired visual image. The inner surfaces are coated with a polymer, which is rubbed so that the liquid crystal material at one surface lies perpendicular to the other. Across the film of liquid crystal, the molecules form a 90° twist.   On the outer surface of the glass plates, polarizers are placed so they are parallel to the liquid crystal orientation and perpendicular to each other. in the "off" state, light entering the first polarizer is guided by the liquid crystal layer twist to the second polarizer, through which it is transmitted. When the cell is energized, the LC material is aligned with the electric field; light transmitted through the first polarizer is blocked by the second polarizer, forming a dark image. The effect may be reversed if the polarizers are placed parallel to each other, and a light image on a dark background is formed The TN technology comes in a single coloration, it is Black characters on a gray background.  It is the least expensive, but has the lowest visual quality, primarily in viewing angle.   SUPER TWISTED NEMATIC (STN) LCDs Although Twisted Nematic LCDs may be driven in a time multiplexed fashion to increase the amount of information displayed, they are restricted in terms of reduced contrast and limited viewing angle. To achieve more highly multiplexed displays, supertwist technology is employed. Super Twisted Nematic LCD's have a twist that is greater than 90 but less than 360 degrees. Currently most STN displays are made with a twist between 180 and 270 degrees. The higher twist angles cause steeper threshold curves which put the on and off voltages closer together. The steeper thresholds allow multiplex rates greater than 32 to be achieved.   In this type of display, the LC material undergoes a greater than 90° twist from plate to plate; typical values range from 180 to 270°. The polarizers in this case are not mounted parallel to the LC at the surface but rather at some angle. The cell, therefore, does not work on a light "guiding" principle, as in Twisted Nematic LCDs, but instead on a birefringence principle. The position of the polarizers, the cell thickness, and the birefringence of the LC are carefully chosen to result in a particular color in the "off" state. Usually, this is a yellow-green to maximize the contrast ratio. The LC in the cell is "supertwisted" that will give it the ability to use a high multiplex rate. As the twist is increased, the LC molecules in the middle of the layer are aligned with the applied electric field by smaller changes in voltage. This gives rise to a very steep transmission vs. voltage curve, allowing up to 240-line multiplexing. The STN technology comes in two colorations, Green STN and Silver STN.  The STN-Green has Dark Violet / Black characters on a Green background. The STN-Silver has Dark Blue / Black characters on a Silver background.  It is in the middle of the road as far as cost, but has very good visual quality. The contrast is similar to TN technology.   Film Compensated Super Twisted Nematic (FSTN) LCDs The most recent advance has been the introduction of Film compensated Super Twisted Nematic (FSTN) displays. This adds a retardation film to the STN display that compensates for the color added by the birefringence effect. This allows a black and white display to be produced and provides for a higher contrast and wider viewing angle. The FSTN technology comes in a single coloration, Black characters on a White / Gray background. Of the three technologies listed here, it is the most expensive, but it has better viewing angles and contrast that the STN technology listed above.

Capability Index is a metric used to evaluate process capability and show how capable process is in terms of meeting customer requirements. Cp and Cpk indices represent the potential (within) process capability. Cp compares the width of a two-sided specification limits to the effective short term width of the process Cpk compares width of the specification and width of the process while also accounting for any change in process average (location of central tendency) Cp is expected to be greater than 1.33 and Cpk = Cp for a perfectly centered and capable process.

·      Cpk can be improved by examining the current process flowchart, removing areas of duplication / unnecessary steps, prioritize improvement and draw new control charts to evaluate how the effect of these changes

Twisted nematicresponse time

statistical control). In other words, Cp = Voice of the Customer/Voice of the Process = (USL-LSL)/(6*SD) where SD= Standard Deviation and denoted by 'Sigma' symbol. A Cp value of >= 1,  indicates that process is technically capable. A Cp value of 2 represents that process performs at 6 sigma level. A Cp value of < 1 indicates that the process is poor.

Cp and Cpk are two capability indices which are used as baseline measurement in measure and control phase. These indices measures common cause variation within subgroup and short term only. These are the statistical measurements to report process capability.

Explain the inference of the Cp and Cpk values that you get for the given data and give some inputs on the kind of action required.

Twisted Nematic (TN),  Super Twisted Nematic (STN), Film Compensated STN (FSTN), and Color STN (CSTN) are the terms used to describe four types of Liquid Crystal Displays, each twisting the orientation of the light passing through the Liquid Crystal Display structure differently to effect contrast and coloration. We also compare coloration, viewing angles, and costs between the technologies.

- Once the Process is centered - Mean average value is obtained, the Cp & Cpk value will be improved & Standard Deviation will be reduced

3.Ideal value for a Cpk should be either at 1.33 or 1.66(close to 4 or 5 sigma) since there can be space for a process drift either to the left or right of the nominal value (target value).

twisted nematic(tn) technology characteristics

4. Applying the formulas which we discussed above, for Cpku and Cpkl , we find the values for them as Cpku=(24-21.5)/(3*0.75)= 2.5/2.25=1.1111; Cpkl=(21.5-18)/(3*.75)=1.5555; Cpk=Min(Cpku,Cpkl)=Min(1.11,1.55) = 1.11

Cp, Cpk are Process Capability Indices. Process Capability is an inherent variability of a given characteristic in a stable process. It represents process performance

In this type of display, the LC material undergoes a greater than 90° twist from plate to plate; typical values range from 180 to 270°. The polarizers in this case are not mounted parallel to the LC at the surface but rather at some angle. The cell, therefore, does not work on a light "guiding" principle, as in Twisted Nematic LCDs, but instead on a birefringence principle. The position of the polarizers, the cell thickness, and the birefringence of the LC are carefully chosen to result in a particular color in the "off" state. Usually, this is a yellow-green to maximize the contrast ratio. The LC in the cell is "supertwisted" that will give it the ability to use a high multiplex rate. As the twist is increased, the LC molecules in the middle of the layer are aligned with the applied electric field by smaller changes in voltage. This gives rise to a very steep transmission vs. voltage curve, allowing up to 240-line multiplexing. The STN technology comes in two colorations, Green STN and Silver STN.  The STN-Green has Dark Violet / Black characters on a Green background. The STN-Silver has Dark Blue / Black characters on a Silver background.  It is in the middle of the road as far as cost, but has very good visual quality. The contrast is similar to TN technology.   Film Compensated Super Twisted Nematic (FSTN) LCDs The most recent advance has been the introduction of Film compensated Super Twisted Nematic (FSTN) displays. This adds a retardation film to the STN display that compensates for the color added by the birefringence effect. This allows a black and white display to be produced and provides for a higher contrast and wider viewing angle. The FSTN technology comes in a single coloration, Black characters on a White / Gray background. Of the three technologies listed here, it is the most expensive, but it has better viewing angles and contrast that the STN technology listed above.

This Cp relates to the process spread. it is a normally distributed population, 99.73% of the variation is within the + 3 std deviations of the process average. The Cp compares the specification width to the Process Width and is the capability the process could acheive.

If Cp portrays the capability to meet the customer specification limits, then why do we need Cpk. The answer is that Cp does not consider how well the output is centred on the target value. Cpk addresses the proximity of the centring of a process related to the spec. limits. Cpk splits the Cp into 2 parts, Cpkl and Cpku.

Cp is a short term index and straightforward  indicator of process capability which doesn't account for its mean being centred. Higher the values reflects narrower the spread an d more precise. And it does not tell the location of spread, only tells about whether the process is capable or not.

consistently hit a target within the goal post. Imagine the coach wants the football to be hit on topmost of the centre of the goal posts (or any other part)? Why ? Because goalkeepers normally try to distract the kickers(football players) and makes a pre-meditated move. Therefore , it is imperative that players hit their

Twisted nematicliquid crystal

practice-penalty goals consistently at the same target position as much as possible. While Cp talks about slotting of goals , Cpk talks about how much variation or drift is there in hitting the goals at topmost of the centre of the posts.

This indicates process data points are in distributed with in 3 Sigma limits, but process mean has shifted towards the upper limit. this means chances of getting the deviations above specification.

When Cp/Cpk would be high : Example 2: Imagine a practice session going for a shooting competition which is bound to happen in a week. A team of 5 is trying its luck , keeping in mind the competition would be stiffer in the actual competition. The team is aiming a point of 9.8 (out of 10), which could a potential medal winning score ,as per the team. The Qualifying range for the competition is 9.3 and above.  If the team is consistently shooting 9.3 and beyond 9.3 say upto 9.5 , then the Cp value is good(high). But if the team is consistently shooting near say 9.7 or even 9.8, then the Cpk is good or high.

2.However, Cpk value of 1.11 conveys that the process sigma is 3.33 . Formula for calculating Sigma Level = 3 *Cpk = 3 * 1.11 =3.33 . So if the sigma level is 3.33, then it shows that there is plenty of variation and there are so much defects for a process operating just over 3 sigma.Therefore, the variation needs to be reduced. Thats the reason why we look for Cpk . Remember from CP perspective it looked like good until we found this now !!

- when the remove the Variations in the Process,  the process will be in control & also the mean value can be obtained close to the target mean.

This is very unrealistic to tell about process capability by considering only one factor only. Because sometimes a process can be more precise but it can be shifted towards any if its limits. And if it is shifted towards any upr or lwr limits which means there is probability to produces products which are out of specifications limits. And Cp doesn't provide any Information regarding the same so it is necessary to see other factors to find out exact scenario of the process that where we should do improvement like improve standard deviation or shifts mean.

Applause for all the respondents- Vijaya Mohan K, Avik Chatterjee , Vastupal Vashisth , N S Sri Kumaresh Prasath, Anyonyvinod, Vishnukiran L S, Husna Banu, Nilesh Akre, Nagaraj Kailas, Vinay Warkhade Patil, D. Nandakumar, Karthik Marimuthu

Twisted nematicLCD

Cpk of value 1.1111 means its barely capable process, because it produces 64 ppm but less than 2700 non-conforming ppm. In this case, the process width is touching the specification width.

Q. 101  Assuming that - Upper Specification Limit = 24, Lower Specification Limit = 18,  The average = 21.5 and Standard Deviation (within) = 0.75,  Cp and Cpk can be calculated using the calculator at https://www.benchmarksixsigma.com/calculators/process-capability-index/

the Cpk value 1.11 infers both the process spread and the process mean, Cpk cosiders the location of the Process mean and as Cp is > Cpk it infers that the process is not centered and it is recommended to reduce the variation in the process.

In our example as Cp is good ,variation is acceptable.As Cpk is bad  (not equal to Cp) and it is less than Cp value, we need to shift the the Mean  to center the process within specification limit without increasing variation

On the outer surface of the glass plates, polarizers are placed so they are parallel to the liquid crystal orientation and perpendicular to each other. in the "off" state, light entering the first polarizer is guided by the liquid crystal layer twist to the second polarizer, through which it is transmitted. When the cell is energized, the LC material is aligned with the electric field; light transmitted through the first polarizer is blocked by the second polarizer, forming a dark image. The effect may be reversed if the polarizers are placed parallel to each other, and a light image on a dark background is formed The TN technology comes in a single coloration, it is Black characters on a gray background.  It is the least expensive, but has the lowest visual quality, primarily in viewing angle.   SUPER TWISTED NEMATIC (STN) LCDs Although Twisted Nematic LCDs may be driven in a time multiplexed fashion to increase the amount of information displayed, they are restricted in terms of reduced contrast and limited viewing angle. To achieve more highly multiplexed displays, supertwist technology is employed. Super Twisted Nematic LCD's have a twist that is greater than 90 but less than 360 degrees. Currently most STN displays are made with a twist between 180 and 270 degrees. The higher twist angles cause steeper threshold curves which put the on and off voltages closer together. The steeper thresholds allow multiplex rates greater than 32 to be achieved.

It measures how much close to your target and how much consistent to your average. A person can perform more precisely with minimum variation but can be away from its centre and go towards one specification limits and it can be at exactly on average target value but can have more variation.

From this, we can infer that the process is less capable relative to the upper specification limit. Though the variation in the process is acceptable, in order to improve the process performance, the mean needs to be moved away from the USL or back to the middle of the specification limits.

Twisted nematictechnology

The overall sigma value is between 3.3 & 3.4, meaning it has 967 non confirming parts per million, if we take sigma value as ~3.3.

TWISTED NEMATIC (TN) LCDs TN displays have a twist ( the rotation of the molecules from one plane of the display to the other) of 90 degrees or less. All passive direct drive , active matrix, and most passive low level (x2 to x32) multiplexed LCD's have a 90 degree twist. The basic Twisted Nematic (TN) LCD consists of a layer of liquid crystal material supported by two glass plates. The liquid crystal material is a mixture of long, cylindrically shaped molecules with different electrical and optical properties, depending on direction On the inner surfaces of the glass plates are transparent electrodes, which are patterned to form the desired visual image. The inner surfaces are coated with a polymer, which is rubbed so that the liquid crystal material at one surface lies perpendicular to the other. Across the film of liquid crystal, the molecules form a 90° twist.

The Industry guidelines provide the insights whether a process is capable or not. The general accpetable Minimum value for Cp is 1.33 and for the given data the Cp is 1.33, this is an indication of how the process could perform relative to the specification limits (USL and LSL).

R Rajesh has provided clear definitions, examples and inference from the given date explaining the concept of Cp and Cpk in a complete manner.

- In the above mentioned data's, the average is mentioned as 21.5. But as per the actual calculation based on the USL & LSL, the average must be as 21.

- So it is clear that Given average[21.5] has been moved above the target mean [21] & so we have to bring it towards the Mean value

Upper Specification Limit = 24, Lower Specification Limit = 18,  The average = 21.5 and Standard Deviation (within) = 0.75

By understanding both Cp and Cpk, First thing to do is - Variation is in control and still there is an opportunity to shift the Mean of the process to center for improving accuracy.

Let us see the definition of Cp. Cp is the ratio of the specification limits (of a characteristic) to the natural process variation of a process (under a state of

Ideally for a good process capability, its value considered as 2 means specification limits are two times of process limits.

Generally accepted value for Cp is greater than equal to 1.33. So the process is capable but we don't know where its location is whether its shifted or not. Here we are seeing that Cpk is not equal to Cp. It means it has some value of k which is the amount a distribution is centred. So it shows that process is shifted and we need to work on to shift mean back to its centre position rather than to reduce standard deviation, because its easy to shift mean rather than reducing Standard deviation.

Cp and cpk are used to study the process which is stable otherwise the samples will not represent the process. about the inference Cp talks about spread of the values of a sample collected from the process compared with the specification limit. Smaller the spread better the Cp but Cpk talks about how far is the sample mean to spec mean. Sample mean closer to spec mean better the Cpk. In other words Cp is Precision Cpk is Accuracy